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.

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