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.