2004 Tahoe Overheating

[ClayCollins]

My son's 2004 Tahoe LT (5.3 flex fuel) with about 320k miles has been running hot for some time - maybe 240 degrees or more in Houston traffic (its been 100 deg F + for a month now). Towing our boat is really a problem. A couple of years ago, our mechanic found the fan clutch was bad and we had it replaced. I did replace all the leaking plastic heater connections awhile back so they are all good and there's no leaks apparent. We have been having to add maybe a cup of coolant every month of so to top it up which suggests a slow manifold or head gasket leak. There's no water in the oil so we've been letting it go and keeping it topped off. Any ideas what we should be looking at? I hate to start substututing parts like a new water pump or radiator when they're not leaking. Thanks in advance for any advice?

 

[OR VietVet]

Water pumps can have impeller problems and not leak. The water is not being moved around when That happens. At that mileage, I would be worried about the radiator and if you do a radiator, replace the thermostat. Check to make sure the air flow thru the a/c condenser is not clogged. If is, blow it out from the backside of the condenser. Over time, radiators get debris and sediment settle in it and block coolant flow and not allow for good heat dissipation.

 

[Marky Dissod]

... son's 2004 Tahoe LT (5.3 flex fuel) with about 320k miles has been running hot for some time - maybe 240F or more in Houston traffic (its been 100F + for a month now). Towing our boat is really a problem.
A couple of years ago, our mechanic found the fan clutch was bad and we had it replaced.
I did replace all the leaking plastic heater connections awhile back so they are all good and there's no leaks apparent.
We have been having to add maybe a cup of coolant every month of so to top it up which suggests a slow manifold or head gasket leak.
There's no water in the oil so we've been letting it go and keeping it topped off. Any ideas what we should be looking at?

I'm not quite a parts cannon enthusiast.
In a situation like this, though, you would not exactly be firing blind if you started replacing oldest parts first -
radiator, heatercore, thermostat, hoses ...
Also, you did not mention replacing the reservoir cap. If not, whip out the parts derringer, and replace the cap immediately.

If you are using that Dexghoul stuff, I have a memory of when it was notorious for becoming thicker with repeated exposure to air ... ?
Consider switching to a Dexghoul-compatible coolant formulation that is NOT Dexghoul. Prestone & Zerex each make one.
Thoroughly and completely flush the crap out of the engine AND heatercore AND radiator, SEPARATELY - or replace heatercore and radiator.

A leak that is not at the manifold or head gasket may not be mixing with oil, yet could still be responsible for coolant loss.
I once found a strange coolant leak by having my cooling system overpressurized (18psi) in the mechanic's shop, cold.

 

[Fless]

Among other diagnostic procedures, consider removing the valve covers to see if one of the heads is cracked. Do some research on Castech heads of this era.

Here's a link to an explanation:

Chevrolet Silverado 1999-2006 GMT800 Engine Performance Diagnostics

This article will discuss cracked cylinder heads, weak valve lifters, worn valve seals, and positive crankcase ventilation (PCV) fouling....

chevroletforum.com

Check the casting number on your heads (here's a pic of my '04 FF passenger side with the 706 casting number):

 

[rockola1971]

Whats the exhaust look and smell like? An engine burning coolant has a very distinct smell and white smoke.

 

[strutaeng]

The intake manifolds are dry, so it wouldn't leak there. Ditto on the condenser and radiator get clogged up with gunk over the years. My 99 Silverado NBS radiator was at least 1/4 blocked when replaced it. I can post a picture if I remember tomorrow.


I've always ran dexcool and have never had issues. I replace it around 75k-100k or like 5 years. I can't recall what the spec on that is. How old is your coolant? Maybe time to replace it? On the same 99 when it reached 100k a long time ago I did that coolant flush liquid before replacing the coolant...and a short time afterwards my heater core developed a leak (pain to replace BTW). I think it was just a coincidence, but then I thought it had something to do with the flush. But radiator had lasted 260k and was original. I only replaced it to get the larger radiator.

My 06 Suburban runs at middle of the guage, which is like 190-200 IIRC. Similar weather as you. The thermostat you can check by dunking in an old pot of boiling water to confirm it's working properly. Maybe try a lower temperature one, but you don't want to go too low.

Heads are good checking too. Check fan clutch also. It's an easy test.

 

[ClayCollins]

Whats the exhaust look and smell like? An engine burning coolant has a very distinct smell and white smoke.

There’s no white smoke or odd smell. Maybe the coolant leak is so minor it’s not really showing up in the exhaust.

 

[ClayCollins]

Among other diagnostic procedures, consider removing the valve covers to see if one of the heads is cracked. Do some research on Castech heads of this era.

Here's a link to an explanation:

Chevrolet Silverado 1999-2006 GMT800 Engine Performance Diagnostics

This article will discuss cracked cylinder heads, weak valve lifters, worn valve seals, and positive crankcase ventilation (PCV) fouling....

chevroletforum.com

Check the casting number on your heads (here's a pic of my '04 FF passenger side with the 706 casting number):

View attachment 407741

Interesting. I’ll get my son to check the casting number. There’s no foam in the oil whatsoever and no white smoke in the exhaust.

 

[ClayCollins]

The intake manifolds are dry, so it wouldn't leak there. Ditto on the condenser and radiator get clogged up with gunk over the years. My 99 Silverado NBS radiator was at least 1/4 blocked when replaced it. I can post a picture if I remember tomorrow.


I've always ran dexcool and have never had issues. I replace it around 75k-100k or like 5 years. I can't recall what the spec on that is. How old is your coolant? Maybe time to replace it? On the same 99 when it reached 100k a long time ago I did that coolant flush liquid before replacing the coolant...and a short time afterwards my heater core developed a leak (pain to replace BTW). I think it was just a coincidence, but then I thought it had something to do with the flush. But radiator had lasted 260k and was original. I only replaced it to get the larger radiator.

My 06 Suburban runs at middle of the guage, which is like 190-200 IIRC. Similar weather as you. The thermostat you can check by dunking in an old pot of boiling water to confirm it's working properly. Maybe try a lower temperature one, but you don't want to go too low.

Heads are good checking too. Check fan clutch also. It's an easy test.

Thanks for the info. We’ve not flushed to coolant, but I figured with all the heater hose replacements and topping off, we’ve probably swapped out all the coolant at least once in the last 8 years we’ve owned the truck. I’ll use one of my coolant test strips to confirm it’s ok. I’ll bet an upsized radiator would be a good idea. Do you recall which one you installed? The fan clutch is a year old, but worth checking. How do you test for a bad fan clutch?

 

[ClayCollins]

Water pumps can have impeller problems and not leak. The water is not being moved around when That happens. At that mileage, I would be worried about the radiator and if you do a radiator, replace the thermostat. Check to make sure the air flow thru the a/c condenser is not clogged. If is, blow it out from the backside of the condenser. Over time, radiators get debris and sediment settle in it and block coolant flow and not allow for good heat dissipation.

Good tips. Thanks! Changing out the water pump would also give us the opportunity to fix the annoying timing cover leak. I think I’ll start with a new radiator cap. It does overflow when it gets particularly hot.

 

[strutaeng]

Thanks for the info. We’ve not flushed to coolant, but I figured with all the heater hose replacements and topping off, we’ve probably swapped out all the coolant at least once in the last 8 years we’ve owned the truck. I’ll use one of my coolant test strips to confirm it’s ok. I’ll bet an upsized radiator would be a good idea. Do you recall which one you installed? The fan clutch is a year old, but worth checking. How do you test for a bad fan clutch?

The 4.3 radiator on the trucks is like 27" IIRC. I don't know if that sze radiator was also used in other models. The larger sized radiator is 34" (which is the one used for dual electric fans too.) I only replaced mine because I wanted to upgrade to a radiator with engine oil cooler, but I haven't added those cooler lines yet. That's more for like heavy towing.

On the fan clutch if I remember correctly, you are supposed to turn the blades by hand on a completely cold engine. At operating temperature with engine off, you should not be able to turn the fan blades by hand.

 

[ClayCollins]

I'm not quite a parts cannon enthusiast.
In a situation like this, though, you would not exactly be firing blind if you started replacing oldest parts first -
radiator, heatercore, thermostat, hoses ...
Also, you did not mention replacing the reservoir cap. If not, whip out the parts derringer, and replace the cap immediately.

If you are using that Dexghoul stuff, I have a memory of when it was notorious for becoming thicker with repeated exposure to air ... ?
Consider switching to a Dexghoul-compatible coolant formulation that is NOT Dexghoul. Prestone & Zerex each make one.
Thoroughly and completely flush the crap out of the engine AND heatercore AND radiator, SEPARATELY - or replace heatercore and radiator.

A leak that is not at the manifold or head gasket may not be mixing with oil, yet could still be responsible for coolant loss.
I once found a strange coolant leak by having my cooling system overpressurized (18psi) in the mechanic's shop, cold.

I new radiator cap is going to be step 1. I’ll bet the o-ring is bad and allowing coolant to escape and also limiting the pressure in the system.

 

[strutaeng]

Here you go:

Size comparison and the gunk on the old radiator.

 

[ClayCollins]

Here you go:

Size comparison and the gunk on the old radiator.

34” vs 28”. Big difference. Is it a GM part and a direct replacement?

 

[OR VietVet]

34” vs 28”. Big difference. Is it a GM part and a direct replacement?

Do you have auxillary/rear a/c? That makes a difference on the application. What is the width of the existing core? A hint for the future, flushing cooling system is not designed to FIX a problem, it is MAINTENANCE. You can get lucky though. If the heater hoses are approximately the same temp, coming in and out of heater core, it is ok. You can also replace 10 radiators, but if the air flow thru the condenser is not addressed, well you may get better engine cooling with the new radiator but you have not fixed all the problem.

 

[strutaeng]

34” vs 28”. Big difference. Is it a GM part and a direct replacement?

Yes, direct fit.

The only thing is that Im pretty sure I reused my 4.3 fan shroud. The plastic fan shroud doesn't cover the entire 34" front, but I'm running it like that and doesn't seem to affect anything, although I haven't done anything towing yet. AC is nice and cold in this heat wave. I'll try to remember to get the larger fan shroud at some point...

You may already have the larger radiator, no? Can you do a quick measure?

 

[Fless]

I new radiator cap is going to be step 1. I’ll bet the o-ring is bad and allowing coolant to escape and also limiting the pressure in the system.

I'd be surprised if the radiator has a cap; if it does, it's not OE. There should be a pressure cap on the surge tank, which is the only place to add coolant without opening the system (e.g., removing a radiator hose).

 

[houstontaylor]

This may not be the cause of your trouble but my radiator fan attached to the engine on my 2003 Tahoe didn't cool well idling in hot weather in Houston even with a good clutch, but was okay at highway speeds. This meant insufficient AC cold output in my case. Not enough air flow over the radiator at low speed/engine rpm. I thought about trying to retrofit an electric fan(s) to the radiator but never have done that.

 

[Marky Dissod]

This may not be the cause of your trouble but my radiator fan attached to the engine on my 2003 Tahoe didn't cool well idling in hot weather in Houston even with a good clutch, but was okay at highway speeds.
This meant insufficient AC cold output in my case. Not enough air flow over the radiator at low speed/engine RpM.
I thought about trying to retrofit an electric fan(s) to the radiator but never have done that.

My stopgap solution to this problem was to have my idles raised to 750RpM.
If you are not going to convert from a mechanical fan to a pair of electrical fans,
you can attach a pusher fan to the front of your AC condenser and wire it to be on whenever your AC is on.

But converting from mechanical fan to electrical fans improves MpG, which is another way of saying, it pays for itself.
So just get it done and enjoy it.

 

[Fless]

If it's the original radiator I'd consider replacing it; it's bound to have some restrictions in it. On the outside, are the radiator or condensor fins bent or clogged with bugs and dirt?

Also make sure that both halves of the fan shroud are in place and properly connected; that will help your clutch fan pull a good amount of air through the radiator at low speeds. The baffles behind the grill on either side of the radiator should also be in good shape and in place to funnel air through the radiator instead of around it.