Getting too hot at idle

[John Moore]

Hey guys,

Middle of summer here in NC and it’s been brutal. Today was right at 100 degrees and I’ve been having problems with my 2000 Z71 Tahoe overheating at idle.

I’ve been having this issue for a while now and here is what I’ve done so far:

Replaced water pump
Replaced the radiator with dual row 2-1/2”.
New thermostat 195 I believe. Whatever it called for.
I have the factory 11 blade fan with a severe duty clutch that stays engaged almost all of the time.
I have the factory Auxiliary cooling fan in front of the condenser (tested).
I don’t know the ratio exactly but it’s dexcool/distilled water good to -15/-20 degrees.

Under the hood I can feel a ton of extremely hot air coming from the fan, the engine bay is ridiculously hot. I have several cars and none of them are this bad.

On the road it runs 189 degrees, not a problem at all. When I have it Idled for a period of time, I’ve seen in climb to 230+ Along with the transmission temp climbing to 220. Today the AC compressor was cycling off, I assume the head pressure was too high, even at 1200 rpm it would not cool itself down much until you get on the road.

The ignition timing at idle is around 22-24 degrees which seems very low to me. For the most part it runs good, I have an intermittent random misfire I’ve been chasing recently but I believe that’s unrelated since I’ve had this issue for a while.

The AC doesn’t cool the best, on a hot day It will not keep up at all. I had the grill off a while back and made sure everything was clean and clear of any airflow obstruction.

Could the condenser be bad internally causing this buildup of heat?

I have no clue what to do next, any help would be greatly appreciated.

Thanks

 

[studigggs]

I'd reexamine your fan clutch. It should not "stay engaged" at all times. Until your temps reach over 200, it should be fairly quiet. When a severe duty clutch engages, its a BIG difference in sound. I had a Hayden SD for a while, but it crapped out after a year (freewheeling at temp). Could be that your fan clutch has failed (leaked viscous fluid) and the "always engaged" sound you're hearing is just the 20-30% engagement and its never engaging at 70-80% which it should do at hot idle.

 

[454cid]

Is the fan shroud in place? This is a 350 correct?

 

[Carlaisle]

Just to be sure we understand correctly: was it already overheating before you replaced the radiator, water pump, and thermostat? And now, with these new parts installed, is it still overheating? Was there any material change in the overheating before/after those parts were replaced? If not, the problem can only be something that has not been changed.

What do you know about the history of this truck? Has it always been this way or is this a recent problem with no clear triggering event? Is the fan blade installed in the right direction? Did you flush the cooling system when you had it torn down to make sure there were no obvious internal obstructions?

Since it works fine running down the road, it is less likely you have an obstruction issue and more likely you have an airflow issue. Which brings us back to 454cid's question about the shroud, my question about the fan direction, and this new question: when the radiator was out, did you actually clean the condenser or just look at it? You might be amazed at what a good back to front hosing out of the condenser can do for your cooling system.

If you end up taking the radiator out again to clean the condenser I would use the opportunity to replace that DexDrool junk.

 

[John Moore]

I replaced the engine a few years ago with a GM crate, has around 20,000 miles on it. This is the first I’ve had this issue with this engine. I took the opportunity to replace the water pump and radiator when I installed the new engine. It never heated up like this at idle until this past year or so. Even though the water pump and radiator are only a few years old, maybe one could be bad.

The fan clutch stays fully engaged a lot of the time, even going down the road it will come on and start roaring. It sounds like a dump truck and moves massive amounts of air. At idle it’s blowing a lot of air and it is HOT. I was under the hood the other evening checking the transmission fluid and the air from the fan was intense.

Fan shroud is in place and the fan is in the correct position. When I inspected the condenser before, I didn’t actually clean it. I straighten a couple of bent fins and it appeared to look clean. I was able to see through it. I should’ve washed it out.

I’ve owned this truck since 2016, never had a problem with overheating at idle until recently and I cannot tell exactly when or why it’s happening. I’ve towed my Jeep around, pulling through mountains, cruising at 75, etc and it’s perfect. Doesn’t get above 190. Just for some reason sitting and idling heats it up. Even last night, I let it sit and idle with the AC on. Outside temp was around 85, and it would slowly go up to 230 after about 20 minutes.

I have always run dexcool in it, and I made the mistake of running full strength after I installed the engine. It was 100%, not diluted with no water at all. It wasn’t until last year that I realized my mistake and drained some of it to replace with water. I don’t know the ratio exactly but it’s no longer thick, it’s very watery and good for -20 degrees.

I only have to add about a quart of coolant every oil change which is around 5-7k miles. I top off the reservoir to the line.

 

[PlayingWithTBI]

I only have to add about a quart of coolant every oil change which is around 5-7k miles. I top off the reservoir to the line.

That was going to be my question - are you losing coolant? Sounds like a blown head gasket. When you have the radiator cap off rev it up a little and look for bubbles. Mine didn't do that, it wasn't blowing white smoke out the tail pipe, oil was clean, coolant was clean, compression check was within 5 Lbs on all cylinders, I was losing about 1/2 gallon of coolant every couple weeks, it ran hot at idle but cool when driving. I popped the heads off and 2 cylinders were burning water! Note the white crust on #6 piston. Maybe you can take a bore scope and look to see if you have the same?

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[1998_K1500_Sub]

I think @PlayingWithTBI has given OP direction.

My comment isn't completely relevant to this thread (given that it appears OP doesn't have a cooling problem), but OP or others who read this thread may find it interesting:

@L31MaxExpress has been posting recently about his experiments with other cooling fans (both mechanical and electrical) and their cooling performance gains / losses. One of his posts is here, and if you dig around I'm sure you'll find others…

https://www.gmt400.com/threads/sanden-4440-install.58192/post-1249217

 

[L31MaxExpress]

Living where it is hot alot of the time, completely normal for a fan clutch to engage at highway speeds as needed and yes it does increase the airflow even at 70+ mph.

I have used an early LBZ duramax blade on a Hayden 2007 6.0L Trailblazer SS severe duty thermal clutch on 2 different setups now. On the van I recently tried a Ford fan, then removes it and trimmed the LBZ fan blade to clear the newer 01-02 shroud on my 97 van so that I could use the newer Donaldson designed GM air filter housing.

I have also discovered the older serpentine style condenser GM used with their extremely wide cores are very restrictive to airflow. I put a modern design parallel flow in its place that is much less restrictive. My 383 stays cool now and my ac blows ice cold even at idle. The Duramax fan moves more air than any other I have tested.

As for ac performance, R134a has never cooled well for me. I have used R152a as well as Duracool or Envirosafe Industrial R134a replacement. All 3 are flammable but then again so is R134a when mixed with highly atomized Pag oil as well as the new $$$$ R1234YF garbage. My mom has a newer Titan with the R1234YF and it has a big flame symbol on the ac label. If flammability was a huge issue we would know about it already with all the R1234YF systems already in the field.

 

[454cid]

That was going to be my question - are you losing coolant? Sounds like a blown head gasket. When you have the radiator cap off rev it up a little and look for bubbles. Mine didn't do that, it wasn't blowing white smoke out the tail pipe, oil was clean, coolant was clean, compression check was within 5 Lbs on all cylinders, I was losing about 1/2 gallon of coolant every couple weeks, it ran hot at idle but cool when driving. I popped the heads off and 2 cylinders were burning water! Note the white crust on #6 piston. Maybe you can take a bore scope and look to see if you have the same?

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How does a head gasket only cause mild overheating at idle? I would think there would me more symptoms. My blown head gasket experience is limited to white smoke and milkshake oil.

OP, Is the Aux AC fan coming on? You said you tested it, but that could have been just putting power to the connector..... doesn't mean it's being triggered by the system. Mine gets triggered by head pressure, and a temp of 225F, but I think that was a late change.

 

[PlayingWithTBI]

How does a head gasket only cause mild overheating at idle? I would think there would me more symptoms

I know, right? I looked for all of the normal symptoms but found none. The white crust on top of the pistons is a tell tail sign.

Edit: Plus the head gasket had 2 blown through passages.