05 Puzzled...High Coolant Temp

[SybrKnite]

Okay first about the Tahoe.

2005 2wd Z71 trailering package 5.3 Auto 147K stock.

After having the Tahoe for 6 months now with no significant problems it began overheating. Driving down a city street at 35 mph noticed the ac got warm and had the HIGH COOLANT TEMP warning come on so I immediately shut off the ac. Stopped to check it out and temp spiked at 250* according to the cluster gauge. No leaks, full reservoir and electric fans both running high. Shut it off to cool and then began driving and spiked again at a stop light. Pulled up on freeway and it dropped back down to around 205 (normal for me). Temp stayed there after several miles so turned the ac back on. Continued driving for a while; even in stop and go traffic with no problems. Got home let it sit idling with ac on, then off with no overheating problems. Two hours later drove to the store and after 5 minutes the temp ran high again. Shut it down then 30 minutes later again on the 5 minute round trip home. Four hours later driving to a friends house it spiked again. Shut off ac and cranked the heat to high and it dropped to around 230* and never got cooler or warmer (night time) till I got home.

Figured it was a faulty thermostat so went and got one with more orange antifreeze. Tested the old thermo in water on the stove and it opened fully at 200* give or take according to my wife's kitchen thermometer. Tested the new one and it opened at the same temp. Replaced the old thermo and filled the radiator and purged it of air. Let it run for a while, no ac, and temp sat at 205* for a few minutes then began rising, fans came on in high speed and continued slowly to 250* so I shut it down.

The radiator pressurizes properly and is clear of any visible debris including the condenser coil, oil cooler and trans cooler. The upper hose seems really hot compared to the lower.

Coolant temp sensor? Water pump not moving coolant the way it should? Can they get weak? Changed a few water pumps on my C/K but not this style. Do they function differently?

Thinking of seeing what it does idling with no thermo installed just to see, but other than swapping in new parts I, which I rather not do...I am at a loss...

I have a meter but no scan tool or hand held temp gauge.

Any advise or comments are welcomed.

 

[Rocket Man]

Sounds like the water pump going out to me. At 147k it's probably due for one anyway as regular preventive maintenance. They're extremely easy to replace on these motors, a few bolts and they even have an O-Ring gasket. If it doesn't fix your problem at least you know it won't be going out on you when least expected.

 

[rockola1971]

If it aint the water pump, "radiator cap" or a thermostat problem and the temp gauge is accurate then you have one of two things going on. (1) Air trapped in coolant system or (2) Blown head gasket pushing exhaust gases into your coolant.

 

[RED TAHOE LS]

The upper hose seems really hot compared to the lower.

Time for a new radiator, gravity flows down through the radiator, when upper/lower hose varies in temperature, there's clogging in the radiator. Good luck and AC Delco is my preference, JMHO.
David g...........

 

[rockola1971]

Ive heard of people having their radiator get clogged up but ive never experienced it myself but I always use deionized water and never use any of that pink or orange crap in any of my rides. Ive seen how silica based crap looks like throw up as it gets exposed to air and/or age and clogs the radiator up. My green stuff never does that.
I usually end up with a tank seal leaking because of the poor crimps when they assemble them. They dont make them like they use too.

 

[SybrKnite]

UPDATE: I pulled the thermostat out and filled the radiator with coolant as much as I could. Then started her up and ran to operating temperature then shut off added more water. Started up again and waited. The temp got to 210* like always. Checked hoses by hand for temp. The hose parts closest to the pump and thermostat housing got hot but the upper hose was cold by the drivers side headlight and felt like it still had air in it cause when squeezed the reservoir level barely moved as opposed to other places on the hoses. The temp rose and the fans came on to no effect...temp continued to rise. I now believe it is a pump issue. I am waiting for it to cool down so I can pull it and inspect it closer and most likely go get a new one.

Any thoughts while this task is completed???

 

[HiHoeSilver]

I'm with Red, change the pump. Cheap and easy. Worth it even if it turns out not to be the problem.

 

[ivin74]

I'm with Red, change the pump. Cheap and easy. Worth it even if it turns out not to be the problem.

The water pump is not working, its not letting the water flow down to the lower hose.

 

[rockola1971]

There are only 2 failures that I know of with these types of pumps. One is a failed bearing and the front mechanical seal leaks causing coolant to leak out of the weep hole and the second is impeller related. The impeller either separates or rusts away from the shaft then there is no pressure generated OR the impeller blades corrode and break off or are totally gone which also causes the pump to generate no pressure. I dont know of any other type of failure. A simple check to see if pressure is being generated is to squeeze the upper radiator hose once the engine is up to temp and you should feel pressure pressing outward on the hose against your hand pressure on the hose. If there is none then either the water pump is not creating pressure OR the thermostat is stuck closed. There could also be a blockage in the coolant path too, which is either dexcool puke or busted off impeller blades.

 

[SybrKnite]

UPDATE:

Well I changed the pump out. Easiest pump ever that I have ever changed out on anything.Filled it with coolant and let it run and then added more. It got warm but then I had a hard time getting the air out. It would get hot but not like before. Had the front raised up and still had air in it. I found the solution by removing the upper hose from the radiator and poured coolant into it holding it much higher than the top of the reservoir. This (pressure) forced out a lot of air. I mean a lot. Then once it started coming out the radiator I reconnected the hose. Since then I have had no problems with it going over 205* idling with the ac on or even in 95* heat in traffic. Runs cooler than before by a few degrees. The old pump was not original to the truck come to find out by the gaskets it used. I could not open the pump to inspect it but it had to be the problem. Took a weekend trip to the Hill Country for a Scout event and never had a problem.

Anyway it is cooling better than before and I have piece of mind this problem is fixed.

I want to thank everyone for their comments and help.

Very Grateful.