Need Help. 2011 Tahoe cooling system will not pressurize.

[Joseph Thomas]

I have a 2011 Chevy Tahoe LTZ with a 5.3 and it has just over 122,000 miles. I noticed that there was an issue a few weeks ago when I had the heater on, and it was set to 75 degrees. It was blowing warm for about a few minutes, then it turned cold. I then turned the heat up to 90 and it blew nice and hot. Then turned it back down to 75 degrees. It blew warm for about a minute or two and then started to blow cold. I check my coolant system and the fluid level seemed to be fine. The overflow tank was at the Max fill line. I inspected the radiator hoses, and the heater core hoses. Both heater core hoses are hot. Both radiator hoses are hot. The top radiator hose has pressure, and the bottom radiator hose has no pressure. My first thought was the thermostat was bad, so I replaced the thermostat. The issue persisted. Then I thought since maybe the pressure was an issue, I replaced the overflow tank cap. Still no fix. I inspected the vehicle all around it could not find any leaks. I then checked the rear heater hoses to make sure if that system was it compromised. Both rear heater hoses are hot and again there are no leaks. I went ahead and flushed the heater core even though I do not think it's clogged because both heater hoses are hot. After I completed this there still is no pressure in the system and I am still losing heat. I went to O'reillys and purchased another reservoir cap just in case the one I purchased before was a bad one; It was not. I then and rented a pressure tester and tested the system. I pump the pressure up to 20 PSI and let it sit there for 10 minutes. The system retained pressure. Both top and bottom radiator hoses were hard, and I could not squeeze them. Now this does not make sense. How come the vehicle cannot create pressure on its own and retain it, but when I put pressure in the system with a pressure tester, it will maintain proper pressure? I'm wondering if it's the water pump? Still I have no leaks . I'm not losing any coolant anywhere. I can't find any moisture around the water pump or where the weep hole would be. Anybody have any answers to this issue? Also, there is no moisture from inside the passenger compartment floor that would indicate the leak in the heater core.

 

[GoToGuyRon]

Ok, you said" top radiator hose has pressure, hard, but bottom hose does not" . Do you understand how the radiator and inlet and outlet hoses function. There is no way to retain pressure in upper hose and not also the same pressure in lower hose. Using your hands isn't accurate. Get pressure gauge. If you have heat incated in all the underhood items, why aren't you focusing on the hvac controller. At first thought you have a controller issue. As you said " it will maintain 95 degrees, but not 75". Is it trying to maintain 75 but it just appears to be to cold? Or is it actually driving the controller to full cold. Try understand the system. This is only based on info you provided. But if ya got heat everywhere but the outlet, ......

 

[Joseph Thomas]

I did use a pressure tester kit. I pumped it up to 20 PSI and the system retained pressure. The first time I checked the hoses I'm pretty sure there was no pressure in the bottom hose but there was pressure in the top hose. Maybe I'm crazy. I have not been able to replicate that. Ever since both hoses have no pressure. When I say no pressure, I mean that I can squeeze and collapse them with my hand. When I tested it with a pressure tester kit, I could not collapse the hoses with my hand. I've thought about the HVAC controller or another electrical component within the system. If any of these things were bad would it keep the cooling system from creating and maintaining pressure?

 

[Foggy]

Sounds to me like you just have air in the system. There are plenty of threads and videos showing the correct "burp" procedure... Try this first..
Then my second choice would be water pump , since you've already done the
cap and thermostat.
Also, do NOT pressurize a cooling system to MORE than the cap is rated for...
That's the max that the components in the system are designed to take.
You will do damage to components if you pressurize too high

 

[Joseph Thomas]

Ok, thanks. I will try and "Burp" the system. I know, I didn't go over the rated 20 PSI. Thanks.

 

[wsteele]

HI Joe, welcome from Idaho.

Maybe one of the cabin/duct sensors is off? Maybe it is reporting a bad temp, given it blows hot at 90, but shuts down quickly at 75.

 

[Joseph Thomas]

HI Joe, welcome from Idaho.

Maybe one of the cabin/duct sensors is off? Maybe it is reporting a bad temp, given it blows hot at 90, but shuts down quickly at 75.

OK, but would that affect the pressure of the cooling system?

 

[wsteele]

OK, but would that affect the pressure of the cooling system?

Sorry, not sure I understand. I must have missed something as I thought I read you had pressure tested the system and all was well on that front.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics, please.

Folks here are already responding to your issue with suggestions. Follow their suggestions, and then report back with the results. We will be here with you, until your issue is resolved.

 

[gooffeyguy]

As long as the system holds pressure when tested, I wouldn't worry about whether or not the hoses feel hard/pressurized while running.

My radiator hoses will feel either soft or hard depending on when I feel them. The thermostat being open or closed will play a big part in that also.

Sent from my SM-G930V using Tapatalk

 

[Joseph Thomas]

As long as the system holds pressure when tested, I wouldn't worry about whether or not the hoses feel hard/pressurized while running.

My radiator hoses will feel either soft or hard depending on when I feel them. The thermostat being open or closed will play a big part in that also.

Sent from my SM-G930V using Tapatalk

I understand that, but if the system cannot pressurize itself and maintain pressure, then there is something wrong. Also, there is the heat issue too.

 

[Joseph Thomas]

I've been out for a couple of days so I finally got around to Burping the system. I used the proper Lisle Funnel. I am located in Central Texas and we have been hit with a winter/ice storm. My Tahoe was cover in ice and today it is 27 degrees here. I stated the Burp process, but she could not get up to operating temperature for the thermostat to open. I let her idle for about 35 min and the temp stopped rising at about 195 degrees. I guess its just too cold here. During those 35 min, I did not see any air bubbles rise in the funnel. I will try again on Tuesday when it warms up and this storm passes.

 

[gooffeyguy]

I understand that, but if the system cannot pressurize itself and maintain pressure, then there is something wrong. Also, there is the heat issue too.

I understand that, but if the system cannot pressurize itself and maintain pressure, then there is something wrong. Also, there is the heat issue too.

Could be the water pump. I recently replaced the water pump on my 2001 because it was leaking coolant. When I pulled the water pump off, the internal vanes had basically disintegrated. I would think this could cause it to not build pressure

 

[Larryjb]

Have you considered the blend door in the HVAC? If the blend door is stuck on the cold side, your coolant may be up to temperature but the air is not being directed over the heater core, therefore cold air.

 

[Larryjb]

Could be the water pump. I recently replaced the water pump on my 2001 because it was leaking coolant. When I pulled the water pump off, the internal vanes had basically disintegrated. I would think this could cause it to not build pressure

I could be wrong, but I would think if his water pump were that bad he'd have an overheating problem.

Pressure is built up mainly by heat, not by the water pump circulating the coolant. When you stop the motor, the system will still remain at 20psi until the system cools.

Don't our radiators have restrictors in line with the radiator? This could account for a higher pressure of water in the radiator and a lower pressure on the water pump inlet hose, which would account for why you could squeeze the lower radiator hose by hand. When you put the tester on, the 20 psi would have been equal throughout the system.

 

[gooffeyguy]

I could be wrong, but I would think if his water pump were that bad he'd have an overheating problem.

Pressure is built up mainly by heat, not by the water pump circulating the coolant. When you stop the motor, the system will still remain at 20psi until the system cools.

Don't our radiators have restrictors in line with the radiator? This could account for a higher pressure of water in the radiator and a lower pressure on the water pump inlet hose, which would account for why you could squeeze the lower radiator hose by hand. When you put the tester on, the 20 psi would have been equal throughout the system.

That makes sense

 

[Joseph Thomas]

Could be the water pump. I recently replaced the water pump on my 2001 because it was leaking coolant. When I pulled the water pump off, the internal vanes had basically disintegrated. I would think this could cause it to not build pressure

Yeah, that is what I'm thinking. However, I don't have any leaks. If the Burp process doesn't work, I may be replacing the water pump anyway.

 

[BG1988]

I've been out for a couple of days so I finally got around to Burping the system. I used the proper Lisle Funnel. I am located in Central Texas and we have been hit with a winter/ice storm. My Tahoe was cover in ice and today it is 27 degrees here. I stated the Burp process, but she could not get up to operating temperature for the thermostat to open. I let her idle for about 35 min and the temp stopped rising at about 195 degrees. I guess its just too cold here. During those 35 min, I did not see any air bubbles rise in the funnel. I will try again on Tuesday when it warms up and this storm passes.

disconnect the fan relays but do watch the temps(it might check engine though don't worry just watch the temps) don't forget to reconnect the fans and cool off the engine with it running...

if you have an aluminium block don't attempt this... as it may cause damage...


that is totally false it should come up to temp without issue.... no one else with a GMT900 that lives in a cold area has that issue..

t-stat is broken or slow and starting to fail...

 

[Foggy]

Just as an FYI: the factory temp gauge is VERY Vague...
It will show 210* - the middle normal operating temps -
All the way from about 185* - 220* ish...
Best to put a scan tool of some sort to see the ACTUAL Coolant Temps
when diagnosing these type of issues.
I was rather surprised several years ago when I put my scanner on
a GMT900... They are ALL the same... It's so the soccer moms don't freak out

 

[shoplizard]

Have you checked the HVAC system for fault codes, I am assuming your Denali has auto HVAC and therefore can be accessed by a scan tool. For the most part, what you are describing is normal operation, the cooling system will not build pressure until the engine temperature exceeds the boiling point of water or the coolant which at your altitude is above 195f which is the opening temp of the thermostat. The fact that you say the HVAC will blow hot air at a high temp setting tells me the engine portion is ok. There may a problem with the HVAC not controlling the temp accurately. This could be a faulty temp sensor in one of the ducts or an issue with the controller. When you increase the interior temp and then change to a much lower temp the HVAC will attempt to cool back down by lowering the outlet air temp to adjust to your new temp setting. This could be more noticeable with the lower outside temperatures. Good luck