DieselTech
I'm Awesome
That looks like oil in the coolant to me.
Overheat and no oil pressure
- Thread starter Heavyhittah59
- Start date
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Greetings my fellow GMT400 big block pilot. I have a 7.4 Vortec (454 Gen VI big block) in my '99 C2500, and it's my happy space.
Thanks for the clear photos in your status update. Upstate NY is a long way from Hawaii, and sharp
photos help a lot to make my long-distance troubleshooting a little more accurate. (!)
Before we go any further, here's a google search for oil in the coolant that I did. Notice the similarity
between some of these photos and yours: (Google results for oil in the coolant)
****
So while you are reading the following, keep in mind that I need one more photo from you in order
to have a decent amount of confidence in my diagnosis. But more on that in a minute.
So in your original post you expressed a desire to know more about this failure so as to avoid
being taken advantage of by an unscrupulous mechanic. I couldn't agree more with this sentiment,
so let's take a couple of moments to reason through A) how our individual engine fluids can start
mingling, B) where are these fluids mixing with each other, and C) what combos mean that we can
fix the existing engine vs which combos = we need to replace the original engine with a twin from
the Treasure Yard? (Hint: Your pics show a rather unusual {to me} failure, but I think I have an
answer for that.)
****
Here's the 2 main ways that engines leak after an overheat thanks to a blown head gasket:
* Engine coolant > combustion chamber
* Engine coolant > engine oil
And here's a photo of a Vortec 350 cylinder head that's just been removed. Look
for the arrows that show the 2 leaking modes that I just described:
You must be registered for see images attach
By the way, this photo tells a lot of story.
1) In order for the green arrow to occur, we need the head gasket to fail in such a way
that it allows coolant under ~15 psi of pressure to shoot into the (near atmospheric pressure) lifter valley.
(By the way, THIS is the photo I need from you. I need to see what the engine oil looks like when you pull the engine oil dipstick.
IF the oil in your oil pan is *still* 100% oil (no oil/water mousse like your radiator) then this specific failure did *not* happen to your head gasket(s).
For what it's worth, when I've worked on engines where coolant is mixed w/engine oil (or engine oil is mixed into coolant) it always reminded me of mousse: (Mousse)
2) Another way that your head gasket can fail is when the 150+ psi (compression stroke) to ~1150 psi (power stroke)
in the combustion chamber is trying to pressurize your cooling system/making your overflow tank boil angrily.
According to your symptoms I think that you *are* experiencing the leakage shown by the red arrow above.
3) The orange dotted line/crack? This is when your engine oil is clean, your coolant is clean, none of your spark plugs
look steam cleaned, BUT you have some/lot of white smoke pouring out of your exhaust. In English, the location
of the crack in your cylinder head is after the combustion chamber, yet water is still being metered into the exhaust stream.
4) But if you are picking up what I am putting down, I still haven't described what you showed me in your pictures: engine oil
in your coolant. (!)
Now the reason why I'm being so specific is that replacing the head gaskets will *not* cure this, for in the big block Chevy there
are no pressurized oil passages sealed by the head gaskets. (unlike other engine designs) And of course in order to have a
successful leak, you need a pressure differential between the source and the destination.
Long story short, the only way I can account for engine oil into your coolant is where the factory engine oil cooler heat exchanger
(inside one of the radiator end tanks) has sprung a leak. And since your coolant is running ~15 psi, but the oil pump is capable
of 60+ psi, there's plenty of pressure differential to make this cross contamination happen.
****
So given the above, a good troubleshooting mechanic should be able to figure out that the overpressurized cooling system is
head gaskets, but at the same time head gaskets can't explain the engine oil in your cooling system. (mud = mousse :0)
As for the chicken and the egg mystery (ie: what failed first & set all this in motion?) ...if I had to hazard a guess I'm thinking
that the oil in the cooling system wasn't helping with shedding the excess heat from the engine to the air passing through the
radiator.
Getting back to the next picture I need to see that I mentioned earlier? I really need to see the condition of the engine oil when
you remove the dipstick. IF there's *only* engine oil on that stick, then that's a positive sign. Actually, before your pictures I've
always seen coolant in the oil, never oil in the coolant? But this makes sense, for every other engine I worked on with this kind
of failure did NOT have a factory engine oil heat exchanger installed inside the radiator.
****
Moving from your pictures to your missing oil pressure, it again depends on the condition of the oil currently in your oil pan.
IF the heat exchanger only allowed oil to flow in 1 direction (into the coolant) then with fresh oil you might be OK. But if
when the engine was shut off, did the now resting 0 psi oil system take in coolant from the still +15 psi hot cooling system?
IF that's the case, (and we find mousse on the dipstick) then all bets are off, and at the bare minimum you would need to
replace the main, rod, & possibly the cam bearings in order to get your oil pressure back. And of course, the 'while you are
in there' rule would kick in. (Timing chain set, anything else found worn, etc.) A full set of gaskets just to get to all the
fiddly bits.
Back to the cylinder heads. They would need to be pressure tested/checked for cracks, and also for any warpage from all
that heat.
Don't get me wrong - the big block Chevy is pretty rugged/robust, so it's not like a bad overheat on a modern overhead
cam aluminum V8. So it may be possible to salvage your existing engine, but only after a lot of careful checking by a
mechanic with lots of BBC experience.
Or you swap in a Gen VI L29 7.4L 454ci big block out of the local Treasure Yard. But if you decide to do this, you would
want to run at least a compression check against it. And of course take a careful careful look at the fluids before deciding
to adopt it. :0)
****
Hope you find this explanation helpful, for I want you to be as informed as possible when you are interviewing potential
mechanics in order to sort out the good guy(s) from the inexperienced money grubbers who wish to benefit from your
predicament. As Jimi used to ask, "Are You Experienced?" ;0)
Best of luck my friend. If I was your neighbor, I would be living in Hawaii, and that would be a hoot for yours truly.
(Vacationed there, loved that.) But at the same time, as your neighbor I would be looking for every possible way to
get that big block back up on the road and earning it's keep. They aren't exactly fragile, but that engine oil cooler
fouling your cooling system will certainly cause distress in your engine bay.
Best of luck my friend. Be sure to let us know how all this turns out.
Cheers --
Last edited:
Heavyhittah59
Newbie
Aloha brother.
So not to make excuses but when I buy a new car/truck I usually go thru it and change oil, coolant, plugs, etc just for peace of mind. But with my two year old and my wife being pregnant I got the truck and just started sledding around.
Now due to my incompetence and laziness here are pic of the burnt black engine oil also two quarts low
But luckily no coolant or mousse in it
So if I’m understanding you correctly it’s possible I my thermostat failed causing an over pressure possible springing a leak in heat exchanger and cross contaminating the coolant with oil causing not only over heating but loss of oil pressure??
Next steps forward does that mean I can try and flush the coolant system and when it runs clear change the coolant system parts rad,hoses,water pump, thermostat, heater core. Etc?
Mahalo for your guidance and quick response. God bless
Heavyhittah59
Newbie
Attachments
EDIT: TLDR alert. And despite my best efforts to the contrary, the following may need to be read a couple of times in order for it all to come together...
Hello Heavyhittah59,
Good honest status update -- this really helps my troubleshooting thought process for your engine to become sharper in focus.
And I get it. Here we are talking about a mistake on a public stage. Believe me when I say that I've made similar mistakes
that I feel fortunate that they are still under wraps. Mistakes go with the territory of being human. If we learn from them,
then it was a net investment in our lifelong learning process. (At least that's what I tell myself. :0)
But by the same token, admitting a mistake made in public can be very helpful for others in that they can learn from your
experience without having to physically repeat it themselves. So I appreciate your being candid about what happened, and I'm
thinking this all falls under the good karma theory.
Absolutely. Coolant in the oil means at a minimum an automatic full teardown, replacement
of all the etched soft metal bearings, careful inspection of crank journals, checking the entire
valvetrain for excessive wear, etc.
Note: The way I wrote my previous reply I made it sound like coolant in the oil is only a
head gasket failure between a coolant passage & up into the lifter valley. Actually, far
more often it's a failure of the gaskets for the coolant passages at the corners of the
intake manifold and the cylinder heads.
And I think I understand why. Because once upon a time this kind of failure wasn't seen
that often on our V8s. Thinking back to the '60s & '70s, when the block, heads, and
intake were all made of the same cast iron. Since they all had the same coefficient of
thermal expansion, the gaskets between the intake manifold wedged between the 2 cylinder
heads weren't being pulled in 2 different directions every time the engine heated up & later cooled off. (!)
One of the first times I worked on one of these was a buddy's 305 in his '84 Camaro.
He had bought it new, and at ~70K miles without warning he had a bad overheat while
commuting to work. We discovered the mousse/mud in the oil. And upon teardown, that
engine was no bueno. So it got replaced by a 4-bolt 355, taking a failure and turning it into
an upgrade opportunity. :0)
And we traced the co-mingling of the coolant and engine oil back to a failed intake manifold gasket.
And the 305 came from the factory with an aluminum intake manifold sandwiched inbetween a
couple of cast iron cylinder heads bolted to cast iron black.
At this point engineering types would start talking about the different coefficients of thermal expansion (HERE)
between aluminum and cast iron...but we'll just peek over that cliff and keep moving. :0)
****
Given the above, my theory is that the sequence of events leading to a failure like yours is one of 2 possible scenarios:
1)
* Over time, old engine coolant became no longer PH neutral.
* Eventually, the engine oil heat exchanger (inside the radiator) corrodes & springs a leak at the weakest point. 60+ psi oil enters the 15 psi cooling system.
* Oil in the coolant impedes the transfer of excess heat from the engine to the atmosphere, causing bad overheat.
-or-
2)
* Intake manifold gasket fails between your aluminum intake manifold and your cast iron heads bolted to cast iron block.
* Coolant now spews into lifter valley, putting coolant into oil, leading to a bad overheat plus engine bearing erosion.
In your specific case, I say no to the 2nd scenario. Why? Because you have oil > coolant system, but NOT coolant > oil system.
This is an important distinction. Does this make sense?
I think that a marginal thermostat might have been a contributing factor by pushing the
cooling system to it's limits, but again that's just guesswork on my part.
Extra heat can equal extra pressure that the radiator cap has to deal with.
Meanwhile, it's the responsibility of the radiator cap to limit total cooling system pressure to ~15 psi. (Blowing
off excess pressure into the overflow tank.)
Thinking about all this some more, given all the failure info that you've shared, I'm more convinced that for
some reason your 25 year old engine oil heat exchanger failed (assuming your truck still has the original radiator)
...putting engine oil into the coolant. But clearly the intake manifold gasket did not let go, for you still have 100% oil
in your lubrication system.
So at the bare minimum you need a new radiator, fresh oil, and oil filter. But will that be enough...or will more parts require replacement
in order to get your truck back to earning it's keep on the road?
Well, to explain my theory with as few words as possible, we need to travel from NY & Hawaii and meet in Las Vegas.
Seriously, we have to discuss the whole Risk vs Reward aspect of the proposed repair. Especially since we're doing this
on the public stage instead of as a couple of neighbors shoulder to shoulder in your engine bay. In English, while I don't
want you to give up on driving around in your GMT400 in Hawaii, by the same token I don't want to encourage you to
throw good money after bad.
So what I'm describing is a bit of a tight rope. And in order to make the most informed decision possible, we need to
first arm ourselves with a bit of testing and review of the data. And in order to do this you will need to rent {for free}
a cooling system pressure tester from a local auto parts store that offers this service: (cooling system testers free if you bring it back)
Once you have the tester in hand, given the oil in the coolant, we need to first disconnect the engine oil cooler lines
from the radiator *before* we pressurize your cooling system. (We want to avoid the chance of pushing coolant into your lubrication system.)
Another possible concern when testing your cooling system's ability to hold pressure is pushing coolant into a cylinder,
followed by bending the connecting rod when you crank the engine over afterwards, and the piston is forced into an
incompressible liquid.
Given this, it is prudent to pull all 8 spark plugs prior to starting cooling system testing. (Bonus points for taking a group
photo of the plugs for additional diagnostic info.)
Now that I've set the table (ie: you should have free access to a cooling system tester + 2 testing issues to watch out for)
let's discuss what you want to find out. In the perfect world, you would replace the radiator cap with the pressure tester,
pump up your cooling system to what the radiator cap is rated for, (let's say 15 psi) and then watch the needle NOT move
back down as you watch it.
And the best test is to leave the cooling system pressurized overnight, and when you return the next morning there is still
no change in pressure. This tells us that the intake gaskets and head gaskets currently still have functional integrity when it
comes to containing coolant.
On the other hand, if the cooling system pressure drops after you pump it up, then we have to figure out where the leakage
is occurring. There have been anecdotal stories in this forum where the leak couldn't be found, so they cranked the engine
over (with all 8 spark plugs still out) ...and coolant blew out of the cylinder(s) where the head gasket had failed. (And also
sad tales where the cooling system pressure check was done with the spark plugs left in, the engine was cranked over, and
hydrostatic lock occurred. Which means that any possible fix just became much more expensive. :-(
****
So I just reread the above, and even though I wrote this I was starting to wonder where I was going with all this?
A: Without understanding how good / how poor your cooling system is sealed, anything else we try will be a pure gamble, and
risking a major parts cannon episode. Definitely not something I want to persuade a guy supporting his young family to do.
But instead of me deciding for you, I'd like to instead show the options and let you figure out what best fits your situation.
And while you read the following list, keep in mind that we are going to go from least cost / least guarantee of success to
most cost / best guarantee of success. (!)
Scenario #1 -- Engine still good, renew cooling system
* Cooling system overnight pressure check passes.
* Flush cooling system thoroughly. Replace radiator, water pump, & hoses. (Retain/reuse heater core.)
* Engine oil pressure comes back with fresh oil & filter.
Benefit: Truck successfully returned to service without cost of removing cylinder heads in order to replace still OK head gaskets.
Note: This scenario is only possible due to lack of discovering coolant in the oil. Probability: Could happen, but this is a bit of a
Unicorns & Rainbows type happy ending. :0)
Scenario #2 -- Cooling system won't hold pressure for any length of time.
* Cooling system fails pressure test. Remove the cylinder heads, inspect for cracks. Also check for warped heads.
* If the failure is only the head gaskets, then (assuming flat heads) replace head gaskets + all of Scenario #1.
Scenario #3 -- Cooling system won't hold oil pressure + oil pressure does not return with fresh oil.
* Oil pressure was lost during bad overheat, and bearing clearances are now out of spec / too big for oil pressure to be developed by oil pump.
* Can the bearings be replaced and clearances brought back to specification? Or was the crank damaged and now requires turning or replacement?
* If the latter, we're crossing over into it might be less expensive to find a treasure yard engine twin in better condition and swap it out?
* Don't forget, you still have to do all of Scenario #1 in addition to the replacement engine.
That's pretty much the best long distance big picture recovery plan I can write out. IF the overnight cooling system pressure check
passes, then this is the first hurdle to overcome. The second hurdle would be to see if the oil pressure comes back with
fresh oil & filter, or if it remains too low for reliable operation.
In addition, depending upon how bad the overheat was, we may end up with piston rings that have had their spring tension baked out,
and now you end up with excessive piston ring blowby. (Not an absolute, but just a possibility that must be factored into the repair calculus.)
****
Of course, testing = time. And time = money when you are paying a mechanic to do this for you.
So I share all of the above with the hope that you can perform a cooling system pressure check (for free)
+ your time in order to give yourself some much needed info prior to talking to the local garages.
IF the pressure check passes, then if it was me I would seriously consider taking the next step of
changing the oil & filter and seeing if there's any oil pressure? If this test passes, then weigh taking
the gamble on new cooling system bits and returning the truck to service? (Note: the only expenditure
so far would be the free cooling system pressure tester rental + the cost of the oil & filter.)
But even if the cooling system will hold pressure but the engine oil pressure is too low? It's big decision time.
But you will have made an *informed* decision. And hopefully a life lesson. (Been there, done that.)
Sir, you are most welcome. I feel that the time spent in this thread is time invested, not wasted.
Because you have given us the opportunity to think about the consequences of a bad overheat, and
also I got to outline how we can test an engine that's been overheated in order to gain the data that
we need to follow in order to fix this for the least amount of money necessary.
And at the very least, if the mechanic you talk to doesn't differentiate between oil > coolant vs coolant > oil...
find another mechanic. And the more experienced the mechanic, the better your chances of success.
Especially if the mechanic really like Chevy big blocks. (I'm guilty of the bigger the engine the harder I'm willing
to try to revive it. (Obviously this is a character flaw, by allowing my enthusiam for a fun ride to trump being
purely pragmatic. :0)
Hope all of the above is helpful. Don't want to give you false hope, or talk you into giving up on your
GMT400 prematurely. The best answer is to gather the diagnostic data and use it to make an informed decision.
Again, thanks for the candid response to my query. Good stuff for all involved.
Cheers --
Hello Heavyhittah59,
Good honest status update -- this really helps my troubleshooting thought process for your engine to become sharper in focus.
And I get it. Here we are talking about a mistake on a public stage. Believe me when I say that I've made similar mistakes
that I feel fortunate that they are still under wraps. Mistakes go with the territory of being human. If we learn from them,
then it was a net investment in our lifelong learning process. (At least that's what I tell myself. :0)
But by the same token, admitting a mistake made in public can be very helpful for others in that they can learn from your
experience without having to physically repeat it themselves. So I appreciate your being candid about what happened, and I'm
thinking this all falls under the good karma theory.
Absolutely. Coolant in the oil means at a minimum an automatic full teardown, replacement
of all the etched soft metal bearings, careful inspection of crank journals, checking the entire
valvetrain for excessive wear, etc.
Note: The way I wrote my previous reply I made it sound like coolant in the oil is only a
head gasket failure between a coolant passage & up into the lifter valley. Actually, far
more often it's a failure of the gaskets for the coolant passages at the corners of the
intake manifold and the cylinder heads.
And I think I understand why. Because once upon a time this kind of failure wasn't seen
that often on our V8s. Thinking back to the '60s & '70s, when the block, heads, and
intake were all made of the same cast iron. Since they all had the same coefficient of
thermal expansion, the gaskets between the intake manifold wedged between the 2 cylinder
heads weren't being pulled in 2 different directions every time the engine heated up & later cooled off. (!)
One of the first times I worked on one of these was a buddy's 305 in his '84 Camaro.
He had bought it new, and at ~70K miles without warning he had a bad overheat while
commuting to work. We discovered the mousse/mud in the oil. And upon teardown, that
engine was no bueno. So it got replaced by a 4-bolt 355, taking a failure and turning it into
an upgrade opportunity. :0)
And we traced the co-mingling of the coolant and engine oil back to a failed intake manifold gasket.
And the 305 came from the factory with an aluminum intake manifold sandwiched inbetween a
couple of cast iron cylinder heads bolted to cast iron black.
At this point engineering types would start talking about the different coefficients of thermal expansion (HERE)
between aluminum and cast iron...but we'll just peek over that cliff and keep moving. :0)
****
Given the above, my theory is that the sequence of events leading to a failure like yours is one of 2 possible scenarios:
1)
* Over time, old engine coolant became no longer PH neutral.
* Eventually, the engine oil heat exchanger (inside the radiator) corrodes & springs a leak at the weakest point. 60+ psi oil enters the 15 psi cooling system.
* Oil in the coolant impedes the transfer of excess heat from the engine to the atmosphere, causing bad overheat.
-or-
2)
* Intake manifold gasket fails between your aluminum intake manifold and your cast iron heads bolted to cast iron block.
* Coolant now spews into lifter valley, putting coolant into oil, leading to a bad overheat plus engine bearing erosion.
In your specific case, I say no to the 2nd scenario. Why? Because you have oil > coolant system, but NOT coolant > oil system.
This is an important distinction. Does this make sense?
I think that a marginal thermostat might have been a contributing factor by pushing the
cooling system to it's limits, but again that's just guesswork on my part.
Extra heat can equal extra pressure that the radiator cap has to deal with.
Meanwhile, it's the responsibility of the radiator cap to limit total cooling system pressure to ~15 psi. (Blowing
off excess pressure into the overflow tank.)
Thinking about all this some more, given all the failure info that you've shared, I'm more convinced that for
some reason your 25 year old engine oil heat exchanger failed (assuming your truck still has the original radiator)
...putting engine oil into the coolant. But clearly the intake manifold gasket did not let go, for you still have 100% oil
in your lubrication system.
So at the bare minimum you need a new radiator, fresh oil, and oil filter. But will that be enough...or will more parts require replacement
in order to get your truck back to earning it's keep on the road?
Well, to explain my theory with as few words as possible, we need to travel from NY & Hawaii and meet in Las Vegas.
Seriously, we have to discuss the whole Risk vs Reward aspect of the proposed repair. Especially since we're doing this
on the public stage instead of as a couple of neighbors shoulder to shoulder in your engine bay. In English, while I don't
want you to give up on driving around in your GMT400 in Hawaii, by the same token I don't want to encourage you to
throw good money after bad.
So what I'm describing is a bit of a tight rope. And in order to make the most informed decision possible, we need to
first arm ourselves with a bit of testing and review of the data. And in order to do this you will need to rent {for free}
a cooling system pressure tester from a local auto parts store that offers this service: (cooling system testers free if you bring it back)
Once you have the tester in hand, given the oil in the coolant, we need to first disconnect the engine oil cooler lines
from the radiator *before* we pressurize your cooling system. (We want to avoid the chance of pushing coolant into your lubrication system.)
Another possible concern when testing your cooling system's ability to hold pressure is pushing coolant into a cylinder,
followed by bending the connecting rod when you crank the engine over afterwards, and the piston is forced into an
incompressible liquid.
Given this, it is prudent to pull all 8 spark plugs prior to starting cooling system testing. (Bonus points for taking a group
photo of the plugs for additional diagnostic info.)
Now that I've set the table (ie: you should have free access to a cooling system tester + 2 testing issues to watch out for)
let's discuss what you want to find out. In the perfect world, you would replace the radiator cap with the pressure tester,
pump up your cooling system to what the radiator cap is rated for, (let's say 15 psi) and then watch the needle NOT move
back down as you watch it.
And the best test is to leave the cooling system pressurized overnight, and when you return the next morning there is still
no change in pressure. This tells us that the intake gaskets and head gaskets currently still have functional integrity when it
comes to containing coolant.
On the other hand, if the cooling system pressure drops after you pump it up, then we have to figure out where the leakage
is occurring. There have been anecdotal stories in this forum where the leak couldn't be found, so they cranked the engine
over (with all 8 spark plugs still out) ...and coolant blew out of the cylinder(s) where the head gasket had failed. (And also
sad tales where the cooling system pressure check was done with the spark plugs left in, the engine was cranked over, and
hydrostatic lock occurred. Which means that any possible fix just became much more expensive. :-(
****
So I just reread the above, and even though I wrote this I was starting to wonder where I was going with all this?
A: Without understanding how good / how poor your cooling system is sealed, anything else we try will be a pure gamble, and
risking a major parts cannon episode. Definitely not something I want to persuade a guy supporting his young family to do.
But instead of me deciding for you, I'd like to instead show the options and let you figure out what best fits your situation.
And while you read the following list, keep in mind that we are going to go from least cost / least guarantee of success to
most cost / best guarantee of success. (!)
Scenario #1 -- Engine still good, renew cooling system
* Cooling system overnight pressure check passes.
* Flush cooling system thoroughly. Replace radiator, water pump, & hoses. (Retain/reuse heater core.)
* Engine oil pressure comes back with fresh oil & filter.
Benefit: Truck successfully returned to service without cost of removing cylinder heads in order to replace still OK head gaskets.
Note: This scenario is only possible due to lack of discovering coolant in the oil. Probability: Could happen, but this is a bit of a
Unicorns & Rainbows type happy ending. :0)
Scenario #2 -- Cooling system won't hold pressure for any length of time.
* Cooling system fails pressure test. Remove the cylinder heads, inspect for cracks. Also check for warped heads.
* If the failure is only the head gaskets, then (assuming flat heads) replace head gaskets + all of Scenario #1.
Scenario #3 -- Cooling system won't hold oil pressure + oil pressure does not return with fresh oil.
* Oil pressure was lost during bad overheat, and bearing clearances are now out of spec / too big for oil pressure to be developed by oil pump.
* Can the bearings be replaced and clearances brought back to specification? Or was the crank damaged and now requires turning or replacement?
* If the latter, we're crossing over into it might be less expensive to find a treasure yard engine twin in better condition and swap it out?
* Don't forget, you still have to do all of Scenario #1 in addition to the replacement engine.
That's pretty much the best long distance big picture recovery plan I can write out. IF the overnight cooling system pressure check
passes, then this is the first hurdle to overcome. The second hurdle would be to see if the oil pressure comes back with
fresh oil & filter, or if it remains too low for reliable operation.
In addition, depending upon how bad the overheat was, we may end up with piston rings that have had their spring tension baked out,
and now you end up with excessive piston ring blowby. (Not an absolute, but just a possibility that must be factored into the repair calculus.)
****
Of course, testing = time. And time = money when you are paying a mechanic to do this for you.
So I share all of the above with the hope that you can perform a cooling system pressure check (for free)
+ your time in order to give yourself some much needed info prior to talking to the local garages.
IF the pressure check passes, then if it was me I would seriously consider taking the next step of
changing the oil & filter and seeing if there's any oil pressure? If this test passes, then weigh taking
the gamble on new cooling system bits and returning the truck to service? (Note: the only expenditure
so far would be the free cooling system pressure tester rental + the cost of the oil & filter.)
But even if the cooling system will hold pressure but the engine oil pressure is too low? It's big decision time.
But you will have made an *informed* decision. And hopefully a life lesson. (Been there, done that.)
Sir, you are most welcome. I feel that the time spent in this thread is time invested, not wasted.
Because you have given us the opportunity to think about the consequences of a bad overheat, and
also I got to outline how we can test an engine that's been overheated in order to gain the data that
we need to follow in order to fix this for the least amount of money necessary.
And at the very least, if the mechanic you talk to doesn't differentiate between oil > coolant vs coolant > oil...
find another mechanic. And the more experienced the mechanic, the better your chances of success.
Especially if the mechanic really like Chevy big blocks. (I'm guilty of the bigger the engine the harder I'm willing
to try to revive it. (Obviously this is a character flaw, by allowing my enthusiam for a fun ride to trump being
purely pragmatic. :0)
Hope all of the above is helpful. Don't want to give you false hope, or talk you into giving up on your
GMT400 prematurely. The best answer is to gather the diagnostic data and use it to make an informed decision.
Again, thanks for the candid response to my query. Good stuff for all involved.
Cheers --
Last edited:
WHY do you think the oil is "burnt" black?
Used motor oil gets black from soot and other contamination; "burnt" isn't typically a factor.
Two quarts low similarly isn't a life-or-death problem. Ideally, you'd keep the oil level within one quart of "full". I don't see two quarts low as being an engine-killing problem. Are you suggesting that the oil migrated to the cooling system? That IS a possibility.
Doesn't look coolant-contaminated. If you pulled the drain plug and no water/antifreeze came out, I have trouble believing that you had a hole between the oil and the coolant. Oil pressure comes and goes with engine operation. You shut off the engine, oil pressure plummets like a paralyzed falcon. OTOH, coolant pressure increases/decreases with temperature.
So if there's a hole in a heat exchanger, or across a gasket, there's going to be times that the oil pressure is greater than the coolant pressure, and times that the coolant pressure is greater than the oil pressure. IF there's a leak in a heat exchanger, it'd be kinda unusual that it only leaks from the oil side into the coolant side, but not the other way.
IF you had that leak at the intake gasket, coolant pressure comes and goes, but there's NEVER any oil pressure there. So it'd be possible to put coolant in the oil, but not oil in the coolant.
Your coolant LOOKS like it has oil in it. But maybe a previous owner added a heaping helping of some miracle-in-a-can cooling system additive that LOOKS like oil. You have contamination of the coolant, but maybe it's not from the engine oil.
It's impossible to tell from here. If you let that coolant settle, perhaps the oil--if it is oil--will float on top and be obvious.
Maybe the thermostat failed. The thermostat does not control pressure--that's the job of the radiator cap. (Yes, temperature and pressure are related--but--the cap is intended to blow-off excess pressure.
At any rate, if the over-TEMPERATURE caused a gasket problem, oil pressure could blow into the cooling system. But it'd be just as likely that the coolant would then blow into the oil system on shutdown.
You absolutely need to flush, flush, flush...probably with some chemical additives to clean that disgusting coolant out of the entire cooling system. You WILL need to pull the block drains, which on a big-block are separated from the knock sensors. When it's my vehicle, I replace the iron/steel block drain plugs with brass draincocks so this job is easier "next time".
'97 K2500, 7.4L. Note position of block drain in relation to knock sensors, both photos.
Driver's side block drain, w/ draincock.
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Passenger side--note the camera angle is goofy, the draincock is almost horizontal in real life, but looks like it's pointing "up" in the photo. Had to grind some clearance into the 45-degree elbow to clear the dipstick tube.
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You'll want to replace ALL the rubber coolant hoses, thermostat, and rad cap. Thermostats are something of a trouble-area now. Replacement thermostats have a higher failure rate than they used to.
Used to be that every town had a couple of radiator shops. You'd maybe get the radiator "boiled-out"--scale and stuff chemically removed. But with the advent of Chinese radiators, it's cheaper to replace the rad than to clean it. The old "radiator shops" are largely out-of-business. About the same for heater cores.
Hipster
I'm Awesome
Idk, a couple miles cooking and no oil pressure can really wreck some stuff. Compression test, leak down test, cooling system test. I would want answers before throwing money at it "trying".
Severely cooked can crack a block or head.
Severely cooked can crack a block or head.
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Yeah, I was trying hard to answer how the 'engine oil' got into the coolant. I had a good case for the 60 psi oil > 15 psi coolant case,
but had no answer for 15 psi coolant > 0 psi oil, which as we know can last minutes during the typical engine off heat soak.
That's a darn plausible answer. Just because I treat a cooling system one way doesn't mean that the
previous owner wouldn't try something much more creative? Tip of the hat -- good call.
@Heavyhittah59, part of what I like so much about this forum is when multiple minds
start kicking around a problem like this. I had a hole in my diagnostic strategy, and
Schurkey provided a possible answer about the contamination being a human instead of
the engine, and did so from what felt like a collaborative perspective.
Out of curiosity I googled radiator service in Hawaii, and I surprised by the results. Here's a screen snap:
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Of course you may be on a completely different island and this is all a moot point, but it seems that
the island of O'ahu is way more radiator friendly than the finger lakes region of upstate NY? :0)
****
As for figuring out what it's going to take to get your truck running, I'd like to see you flush
your system 'as is', change the oil, and let us know what your oil pressure it. If it's still low
right from a cold start then really going after the cooling system is academic -- for you will
have to first decide whether heroics on your existing engine (or a twin with a guarantee from
the treasure yard) is something you are willing to pursue.
But IF the engine oil pressure is good with fresh oil (assuming your gauge is working correctly)
then I would go to town on the cooling system.
* Find a shop willing to boil out your existing radiator?
* plus all the new parts that Schurkey listed
* verify that the fan clutch is good
* make sure that the PO (previous owner) didn't leave the fan shroud off during previous maintenance
* If you have an A/C condensor in front of your radiator, is it clean and allowing max air to be drawn through it?
****
The bottom line for me is that the engine oil pressure w/fresh oil is the gatekeeper. And if you dodged a
bullet and it's still good, then the next step is will the cooling system pass an overnight pressure check?
And only then would I
Anyway, I wrote the above because Schurkey's line of reasoning actually gives me a glimmer of hope that
we could be dealing with just a weird human choice and not necessarily a serious mechanical failure.
No hurry. No time pressure. And we understand that life happens. But when you make some progress on
this, let us know what you discover.
Best of luck --
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Heavyhittah59
Newbie
Thanks road trip I really appreciate the detailed info and options.
Also thanks for looking up the radiator shops and yes I’m on Oahu.
I was told by the original owner that the motor had been replaced around 200,000 miles and the radiator and other components were brand new. He showed me receipts for the engine and labor but no proof of other parts changed. My guess is he got my trust with the receipts and just added on to sweeten the deal.
My goal is to learn everything I can about this truck and its power plant so I can keep it for years, and use to haul all the dead ev cars to the dump one day.
Saturday I should have my hands on a coolant pressure tester and in the mean time I am going to try clean and reinstall the coolant hoses to pressure test it per your instructions.
??Should I leave out the thermostat??
I also have a friend that is going to lend me a leak down kit so I should have some info on that as well.
I also ordered a digital repair Manual so I don’t have to bother you with accessible info and we can focus on troubleshooting
Mahalo again for your insight and encouragement.
Heavyhittah59
Newbie
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