# Begins to overheat when I turn on the heat



## JLL (Sep 12, 2017)

Classically, with a heater core restriction there is low to no heat coming out of the vents.


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## 2012cruzeFL (May 2, 2018)

So likely not the heater core that is the issue... Could it be air trapped in the system? Any other ideas?


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## JLL (Sep 12, 2017)

2012cruzeFL said:


> So likely not the heater core that is the issue... Could it be air trapped in the system? Any other ideas?


There could be air trapped in the system. When it's beginning to overheat, if you turn the heater off, does it stop overheating?


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## jimmyc (Jun 27, 2020)

Funky temp gauge?


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## 2012cruzeFL (May 2, 2018)

JLL said:


> There could be air trapped in the system. When it's beginning to overheat, if you turn the heater off, does it stop overheating?


Yep, a few seconds after turning the heat off it returns back to normal, slightly below middle of my temp gauge. I will try and burp the system some more. I didn't turn the heater on after changing the t-stat so maybe i didn't get all the air out..


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## JLL (Sep 12, 2017)

2012cruzeFL said:


> Yep, a few seconds after turning the heat off it returns back to normal, slightly below middle of my temp gauge. I will try and burp the system some more. I didn't turn the heater on after changing the t-stat so maybe i didn't get all the air out..


That's most likely your issue. Air gets trapped easily in the heater core and it sounds like the air is now somewhere in the rest of the system. One more question.....What HVAC position setting are you using when the heat is on? Floor, Defrost, Vent?


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## jimmyc (Jun 27, 2020)

Owners manual says (regarding adding anti-freeze) with the reserviour cap off, start motor and wait until upper radiator hose gets hot. Then put reseviour cap back on.

Never had to do that with any previous vehicle...but then, these are the new "advanced" over engineered things (experimental?) "depend on the computer absolutely" mindset. We don't have a choice.. Oh, did I mention (IMO) excessive use of plastic on the motors?

Of course, I could return to a 1958 Buick........


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## 2012cruzeFL (May 2, 2018)

JLL said:


> That's most likely your issue. Air gets trapped easily in the heater core and it sounds like the air is now somewhere in the rest of the system. One more question.....What HVAC position setting are you using when the heat is on? Floor, Defrost, Vent?


I was using vent when heat is on. I will try and get the air out tonight and post and update on if this fixed the issue.


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## JLL (Sep 12, 2017)

Ok. I was curious because if it were a defrost setting sometimes those settings cycle the air conditioning compressor to help with moisture control.


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## Blasirl (Mar 31, 2015)

I was going to suggest making sure the AC is off. If something is wrong with it and it is turned on you could possibly cause overheating. I think the problem though is air in the system. It will need to be "burped" about three times.


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## 2012cruzeFL (May 2, 2018)

Thanks everyone. Seems it was just some air in the system. I opened the radiator cap and let it idle up to operating temp, switched through different heat / defrost settings, ac settings, etc and do not have any overheating issues. Drove about 100+ miles today and had no issues. Next up, my front crank seal :/


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## 2012cruzeFL (May 2, 2018)

JLL said:


> Ok. I was curious because if it were a defrost setting sometimes those settings cycle the air conditioning compressor to help with moisture control.


This explains why my fan was switching on with the defrost coming on... I was wondering why that was happening!


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