High volume oil pump 98 K1500 5.7

[Pinger]

Wild Guess: That's worse than just starting the engine.

You're still spinning the crank and cam on whatever residual oil is on the journals; but with extra time spent wiping the cam lobes along the lifters, loading the lifters without oil pressure to "inflate" them, wiping the rocker arms on the fulcrums, etc. Residual oil is all you have for lube, and you're spending extra time stressing that film.

If the engine STARTS, the oil pump turns significantly faster, making it more effective in pushing oil through the oil galleries to the bearings, but also to the lifters, pushrods, valvetrain, etc.

The above happens at some point (when I do fire it up). Pressure on the dash gauge shows sooner doing this. All I'm doing is priming galleries - as you would on a freshly built engine but with a lowered requirement.

Not to mention the reduced starter engagement time on the unlubed starter drive/flywheel teeth, and increased battery drain.

It is concern for the starter that worries me. It will probably cause me to stop doing it.

 

[L31MaxExpress]

Wild Guess: That's worse than just starting the engine.

You're still spinning the crank and cam on whatever residual oil is on the journals; but with extra time spent wiping the cam lobes along the lifters, loading the lifters without oil pressure to "inflate" them, wiping the rocker arms on the fulcrums, etc. Residual oil is all you have for lube, and you're spending extra time stressing that film.

If the engine STARTS, the oil pump turns significantly faster, making it more effective in pushing oil through the oil galleries to the bearings, but also to the lifters, pushrods, valvetrain, etc.

Not to mention the reduced starter engagement time on the unlubed starter drive/flywheel teeth, and increased battery drain.

The GM delay varies with temperature but it is like 8 reference pulses. That is 2 crank revolutions. The fuel delay is why these engines seem to start right up when they are warm and a little delayed when they are cold.

 

[Road Trip]

I really do not see a need to prelube before starting. I pulled an engine apart a while back that had sat for nearly a decade. All the internal parts still had a nice film of oil present. The oil pump will be spinning before the engine fires. Most GM vehicles have the cranking fuel pulse delayed some number of reference pulses before the PCM pulses the injectors too.

Remember those Slick50 demonstrator engines they ran without an oil pan? Plenty of oil film left to run the minimal amount of time needed.

After having slept on it, I think that last night I was in possession of a solution in search of a problem.

(Ahem...this wouldn't be the first time I've been guilty of this. :0)

Seriously, I've troubleshot/messed with my fair share of engines over the years, ranging
from 'final season winter beaters' to best reasonable upgrade performance builds. In all cases
we were simply trying to make the most of what we had to work with. But thinking back on
all this, *all* these engines could be neatly divided into 2 main categories:

1) Engines that got a mechanical oil pressure gauge. (Some)

2) Engines where we just relied upon the factory oil pressure idiot light / uncalibrated factory
gauge that was long on decoration and short on conveying any real diagnostic info. (Majority)

Thinking about all this some more, I realized that any engine good enough to get a
gauge *always* gave near-immediate oil pressure on startup. About the only variable
worth worrying about was the quality of the anti-drainback valve in the oil filter. (!)

On the other hand, the engines in the latter 'use it up & retire' category had all manner of
ways to communicate that the oil pressure was lagging *after* the engine had started.

Sharp rod rapping for 2-3 seconds before quieting. (With enough practice you can
discern if only 1 rod raps...or if they are all rapping -- there is a difference. :0) Or the
deep bass percussion of a main bearing with excess clearance before the oil pressure builds.
1 or more hydraulic lifters clacking before quieting. (And of course the piston slap that tends
to camouflage the other noises...but lasts longer, until the pistons grow to operating dimensions.)

****

Given all this, instead of noodling over how to best implement a pre-luber, I should instead
try to find out what brand oil filter has a demonstrably better the best anti-drainback valve included.

And then sit back & watch just how fast the oil pressure appears on the gauge, while at the same
time listening carefully for any stray startup sonics. And if I decide to open up the L29, I'll be sure
to get all the clearances as right as rain...and install that mechanical oil pressure gauge...and enjoy the ride.

@L31MaxExpress, thanks for confirming what I was thinking after a full head of sleep. Common
sense always feels better than being driven by unfounded motorhead fears...

 

[georgedunham]

So I changed the oil and filter last night.
4 qts 15-40, 1 qt 20-5, and AC Delco filter
Cold idle went from 36 psi to 42
I haven’t driven it far enough to compare hot idle pressure yet, but I’m optimistic that this is an improvement
I was confident that the engine was wearing out and needed replacing, and when I shared these concerns with a mechanic friend, he wisely asked if I had done compression and leak down tests.
I haven’t but will tomorrow.
He also suggested that I try pushing and pulling on the harmonic balancer.
I tried, but it didn’t budge
He also suggested that I cut open my filter and inspect it for metal. I found one “flake“, likely from the destruction of the filter.
We will see what the results of the compression and leak down are tomorrow, but I am now pretty confident that they will be satisfactory
Maybe my truck identifies as a diesel?
I’m ok feeding it 15-40 if that’s what it really wants

 

[georgedunham]

Ran compression test today
160,160,150,155,155,155,160,160
Decided to not perform leak down
Overall I thought my plugs looked good, a bit of oil on the threads of 1 and 6
Gaps were up to .071.
I installed new ones gapped at .060

 

[L31MaxExpress]

Ran compression test today
160,160,150,155,155,155,160,160
Decided to not perform leak down
Overall I thought my plugs looked good, a bit of oil on the threads of 1 and 6
Gaps were up to .071.
I installed new ones gapped at .060

I started buying plugs gapped at 0.044" long ago for my L31s. There was a TSB from GM long ago on closing the gaps down and GM even had a revised plug for it. I personally witnessed an L31 gain 10 rwhp closing down the plug gaps and it is easier on the craptastic cap and rotors.

 

[georgedunham]

So I think that I may be at a loss right now, as to the smartest course of action.
Why did my oil pressure, on this not worn motor, drop so low?
The thicker motor oil boosted pressure, but at what cost?
New oil pump? - Maybe the pressure relief springs are heat soaked?
New high volume oil pump?
-I know road trip doesn’t like this, but I’m thinking my scrapers aren’t as worn out as they could be, and quite frankly, he’s the only voice out there saying “no!”

 

[Road Trip]

So I changed the oil and filter last night.
4 qts 15-40, 1 qt 20-5, and AC Delco filter
Cold idle went from 36 psi to 42
I haven’t driven it far enough to compare hot idle pressure yet, but I’m optimistic that this is an improvement
I was confident that the engine was wearing out and needed replacing, and when I shared these concerns with a mechanic friend, he wisely asked if I had done compression and leak down tests.
I haven’t but will tomorrow.
He also suggested that I try pushing and pulling on the harmonic balancer.
I tried, but it didn’t budge
He also suggested that I cut open my filter and inspect it for metal. I found one “flake“, likely from the destruction of the filter.
We will see what the results of the compression and leak down are tomorrow, but I am now pretty confident that they will be satisfactory
Maybe my truck identifies as a diesel?
I’m ok feeding it 15-40 if that’s what it really wants

Greetings George,

Really appreciate you posting the results of your changes!

When owners don't close the loop with the results of recommended changes then all we
have for the record is educated guesses. But when folks like yourself report back then
the conversation moves into the 'Empirical Testing' arena, which is much more informative
for the GMT400 community.

Also, the mechanic who recommended the compression test is pretty savvy. No doubt
he's trying to figure out if the entire engine is really tired, or do we just have an OK engine
with a little extra clearance on the rotating assembly?

Also, the removed plugs read nice for the miles that have accumulated on them. Best case is
when they all read very similar to each other, just like what you have in post #35.

****

Of course the next step is to see how much oil pressure is showing on your oil pressure gauges,
see if they agree, and what is the indicated pressure showing at a hot idle? And does the "Check Gauges"
light now remains extinguished?

NOTE: One variable we haven't discussed is the hot idle engine speed. If you have, say, 10 lbs of
hot oil pressure, and for some reason your engine is idling a bit slower than specification, then upping
the idle rpm may improve the indicated oil pressure up to the OK zone? Then again, if it is idling
to specification AND you have an automatic trans, then what you have is what you get. (Don't want
to run afoul of the stock torque converter & have the engine trying to drag me around when stopped.)

By the way, if it was *my* truck, my spark plugs looked like that, and I had a lower than desired hot
idle oil pressure AND a manual transmission, then I wouldn't hesitate to up the idle speed just enough
to give me, say, 10-15 psi of pressure. (I'm not talking 1500 rpm, more like bumped up a smidge to
850-950 rpm in neutral.) Sure, this might reduce engine braking a bit, but driving old successfully
sometimes requires intelligent compromises like this. (And I know that instead of twisting an idle
speed screw we would have to edit the appropriate tables...but I'm just talking hypothetical here.)

EDIT: If this was my truck and I still wanted to boost the hot idle oil pressure, then I wouldn't hesitate
to add in the factory style oil cooler as @L31MaxExpress discusses below. Good stuff!

Again, given the way that you are using your truck, I'm hoping that feeding it the viscosity oil it 'wants'
at this point in it's useful service life will allow you to continue to enjoy your truck for awhile longer.

If she stays quiet & the Check Gauges light stays out, then you should be good to go.

 

[L31MaxExpress]

These right here are worth +10 psi of idle pressure at hot idle on my 383. With the engine heat soaked it would drop to 20 psi @ 750 rpm without them. With the oil cooler installed agin it holds 30 psi at hot idle. Oil temperature can get excessively high in warmer weather without an oil cooler. The hotter the oil gets the less oil pressure you will get. That being said I had a 305 in my 80 Corvette that ran without any issues at all with less than 10 psi at idle. It would make 70 PSI at 4K, but less than 10 PSI at idle. That engine ran for years in my G20 van, my brothers C10 and the Corvette without issues. Its demise was actually a bent rod from hydraulic lock from a seeping head gasket.

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[Road Trip]

So I think that I may be at a loss right now, as to the smartest course of action.
Why did my oil pressure, on this not worn motor, drop so low?
The thicker motor oil boosted pressure, but at what cost?
New oil pump? - Maybe the pressure relief springs are heat soaked?
New high volume oil pump?
-I know road trip doesn’t like this, but I’m thinking my scrapers aren’t as worn out as they could be, and quite frankly, he’s the only voice out there saying “no!”

Hi George,

You just posted this while I was writing my previous response, so let me try and
step through your questions.

1) Re: 'Not worn'. I just looked, and I didn't see where you mentioned how many
miles are on your engine? Given that your '98 is now 25 years old, there's got to be a
few miles on it? When driving old, there's a big difference between 'worn in' vs.
'worn out'. -0- PSI of oil pressure at hot idle is worn out. Or, IF you had excessive
oil consumption, the spark plugs all came out oil-fouled, the compression test showed
lower than normal results AND you had your current oil pressure we would no doubt be
advising you to not drive the engine without repairing it first. (!)

But, from what we can see remotely, your engine seems to fall into the 'worn in'
category. You have good looking spark plugs, and the oil pressure responded
with the new oil viscosity, so at this point I wouldn't worry about changing the
oil pump or worrying about the pressure relief spring. It's extremely rare for
the SBC oil pump to be the weakest link in the oil pressure chain.

Again, if it was *my* vehicle, I would not choose to install a high volume
oil pump for the reasons I mentioned in post #5. FWIW I shared that
guidance based upon hard-won firsthand experience. (ie: I was in a situation
similar to yours, I installed a new high volume oil pump, and the engine started
burning oil like no tomorrow. It was so embarrassing to drive that I pulled the
engine shortly afterwards and put the lasting fix on it.)

****

In English, what I am trying to suggest is that we make the smallest modifications
necessary in order to get *your* engine to stop turning on the 'Check Gauge' light
AND give you an engine-prolonging oil pressure at a hot idle. As the Service Manual
indicated, the oil that you have chosen is still within the guidelines set by the chart
written by the original design engineers.

Does this make sense?

And I don't understand the reference to 'the scrapers'? Please elaborate.

How many miles are on the truck? The engine? Any major work done to it
since new that you are aware of?

And let us know what you end up with when you drive the truck and get
it fully up to temperature.

Thanks in advance --