01 Tahoe overheating- stumped

[OneofFew]

Engine overheated, so I had it towed home. Today, idling quite a while the temp hung around 210 for a while, then the hotter it got, the faster the temp rose. I turned off the a/c at about 230 degrees a raised the idle, the cooling fan was audible. Temp kept rising.

Things I have checked- cooling fan seems to work, tapping the throttle at any engine temp seems to produce the same level of fan noise, so I am not sure if there is a fan clutch issue.
Water pump not leaking, flow in coolant hoses to radiator evident, so I think the thermostat is good.
checked the temp at the coolant out flange and the thermostat flange and found about a 40 degree drop between the 2 readings.
Coolant is a bit thin, will check its dilution/ boil temp shortly. No concerning level of rust evident in the coolant.
At this point I am not sure if I have insufficient water pump flow, fan clutch not engaging fully or insufficient cooling of across the radiator. Frankly the other day driving it, it should not have overheated even if it had no cooling fan since I was cruising country roads. Just the air flow across the radiator should have kept it cool.

 

[Walkercraig01]

have you tried just turning the heat on to see if tt drops? what kind of noise does the fan make exactly?

 

[ScottyBoy]

Have you tried ckeanicl the radiator? I'm not talking about flushing the tanks, I'm talking about the fins. Remove the front grill, the fan shroud, (and the fan if you can, because that will give you even better access) and spray the radiator and AC condenser with a hose to get off all the dirt, bugs, and whatever other debris us all in the fins. After I cleaned mine off a while back, I noticed a huge improvement.

 

[OneofFew]

quiet at idle and WOOO at 2k.

 

[OneofFew]

Have you tried ckeanicl the radiator? I'm not talking about flushing the tanks, I'm talking about the fins. Remove the front grill, the fan shroud, (and the fan if you can, because that will give you even better access) and spray the radiator and AC condenser with a hose to get off all the dirt, bugs, and whatever other debris us all in the fins. After I cleaned mine off a while back, I noticed a huge improvement.

I haven't checked for debris obstruction, but from the engine side it looks pretty good. Will check, thanks.

 

[Doubeleive]

with the engine off, reach in and try to spin the cooling fan by hand, it should be firm and only move a little, if it is frozen or spins freely then the clutch is shot, my opinion for the radiator is if it is over 5 years old yank it and replace it they get clogged up inside and just don't work properly anymore it's solved the problem for me more than a couple times.

 

[OneofFew]

I did a bit of investigating and if this turns out to be resolved, I will feel stupid, but I have to wait out the stormy weather right now.
I tested the coolant and found it to have a boiling point of 220 :/ It looks green enough, but evidently looks are deceiving. Evidently someone had converted it from dexcool, but I could still tell it was contaminated. I also removed the fan shroud to inspect the fan and clutch and radiator. I am not convinced the fan clutch is operating properly, will check with engine warm to see if it is any harder to turn than at engine cold. so far every time I have checked, it is easy to turn but does not spin freely. Noise wise it seems to make no difference with engine hot or cold, raising the RPM does increase the fan speed.
Radiator looks in good condition. I pulled the thermostat housing and found no T-stat :? SO I went to the AP store and got coolant and distilled water and a thermostat while the cooling system drained.
AS soon as this rain stops I will be able to run the engine to see if this fixed it. This may be a case of a lazy fan clutch and boiling coolant.

 

[Doubeleive]

I did a bit of investigating and if this turns out to be resolved, I will feel stupid, but I have to wait out the stormy weather right now.
I tested the coolant and found it to have a boiling point of 220 :/ It looks green enough, but evidently looks are deceiving. Evidently someone had converted it from dexcool, but I could still tell it was contaminated. I also removed the fan shroud to inspect the fan and clutch and radiator. I am not convinced the fan clutch is operating properly, will check with engine warm to see if it is any harder to turn than at engine cold. so far every time I have checked, it is easy to turn but does not spin freely. Noise wise it seems to make no difference with engine hot or cold, raising the RPM does increase the fan speed.
Radiator looks in good condition. I pulled the thermostat housing and found no T-stat :? SO I went to the AP store and got coolant and distilled water and a thermostat while the cooling system drained.
AS soon as this rain stops I will be able to run the engine to see if this fixed it. This may be a case of a lazy fan clutch and boiling coolant.

if there was no thermostat it would most likely just run cold, but I guess there are instances where it might not depending on the weather, etc.

 

[OneofFew]

if there was no thermostat it would most likely just run cold, but I guess there are instances where it might not depending on the weather, etc.

True, the lack of a T-stat can't be the cause for the overheating, but interesting no less. I do not buy new, always buy old stuff and do all my own work, so I am often amazed by the shoddy crap I find.

 

[swathdiver]

Back to Dexcool? These motors are not made to run on the green stuff anymore.