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CarQuestionGuy, Technician
Category: Car
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Experience:  ASE Master Auto Technician for 5 years, ASE Refrigerant Handler, ASA, iATN
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I have a 2007 Saturn Aura 3.5L. The temp. gauge needle moves

Resolved Question:

I have a 2007 Saturn Aura 3.5L. The temp. gauge needle moves from mid range to hot. Also, when the heater is on the air goes from hot to cold and then back to hot. The coolant level is normal when the engine is cold. What is going on?
Submitted: 8 years ago.
Category: Car
Expert:  CarQuestionGuy replied 8 years ago.
Thanks for using Just Answer

It sounds like you have air trapped in your cooling system. The reason that the air from your heater goes from hot to cold is that there is air passing through the heater core, which makes the air cold, then after the air passes hot coolant goes through it making it warm again.
To get the air out is rather difficult sometimes so it would ba easier if you took it to a good repair shop, but I can tell you a couple ways you could try yourself as well.
Also, if there is air in your system you might have a leak somewhere that you should watch for.

Let me know if you need anything else.
Customer: replied 8 years ago.
I don't mind to try and get the trapped air out. As long as it doesn't get to advanced. Thanks for your help!
Expert:  CarQuestionGuy replied 8 years ago. need to top off the coolant as full as you can get it. Then start your car for about two minutes. Then recheck the level and top it off again. After that let it run and get up to operating temp, then turn it off and let it cool. Recheck the coolant level and top off if needed. Then restart it and let it get as hot as it will without going into the red. Many times it will go to almost overheating then drop back down so be sure to let it get almost to the red. After this, let it cool back down and recheck the coolant level and add if needed. Sometimes you can jack the front of the car up to help get the air out while the car is running at operating temp.
The goal here is to get the thermostat to open and let all the air out of the engine without overheating it.
Let me know if you need anything else.
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