My car is occasionally overheating and heat turns from hot to cold what could cause this?

Tiny
DMARIE86
  • MEMBER
  • 2008 CHRYSLER PACIFICA
  • 66,000 MILES
About a month ago my 08' Chrysler Pacifica, stalled and the battery light came on, we restarted and continued driving home when it started to overheat. After checking everything out there were no leaks, no noises, smells or smoke. We changed the upper radiator hose it seemed very stretched out. The alternator then went and we lost all power to the car. Replaced that drove it again started to overheat then shut off. Mechanic said the alternator was bad and battery was dead. Put a new alternator and battery in then changed the thermostat. It starts off fine the heat works then heat turns cold and it starts to over heat. What could cause this?
Thursday, November 10th, 2011 AT 2:01 PM

10 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Check the antifreeze level, it may be low if it is then have the car checked for leaks. you may have a bad intake/head gasket and leaking internally.

Here is a guide to check for a head gasket failure which is common.

https://www.2carpros.com/articles/head-gasket-blown-test

Please let us know what you find. We are interested to see what it is.

Cheers
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Thursday, November 10th, 2011 AT 2:22 PM
Tiny
DMARIE86
  • MEMBER
  • 6 POSTS
The coolant seems to be fine. It does loose some when it overheats out of the top. But doesnt seem to be leaking otherwise
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Thursday, November 10th, 2011 AT 2:33 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
A head gasket problem fills the heater core with exhaust which doesn't heat up, these two problems are related.
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Thursday, November 10th, 2011 AT 2:38 PM
Tiny
DMARIE86
  • MEMBER
  • 6 POSTS
I'm going to have checked tomorrow. Now wouldn't there be other signs of a head gasket problem?
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Thursday, November 10th, 2011 AT 2:40 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Not necessarily, other htan a coolant use and heating problems which you are experiencing.
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Thursday, November 10th, 2011 AT 2:43 PM
Tiny
DMARIE86
  • MEMBER
  • 6 POSTS
I just went to check the fluid because we changed the thermostat yesterday and tapped it off. The fluid is the same. The car doesn't over heat until you've driven it for 20 min or so. And usually it starts when its idling and once it moves past 1/2 it goes quickly to hot. Not sure if this changes things?
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Thursday, November 10th, 2011 AT 2:52 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
You might have a stuck thermostat.
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Thursday, November 10th, 2011 AT 3:15 PM
Tiny
DMARIE86
  • MEMBER
  • 6 POSTS
That would be ideal. What about trapped air? Rather that then a cracked head. Im hoping for good news only had the car 5mo! Warranty is up dealership we got it from is a joke. Not the best choice too late now!
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Thursday, November 10th, 2011 AT 3:18 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
If air is trapped in system, the coolant level in the pressure container would drop when the engine is cold.

This is a description of what would happen.

COOLING-AERATION

Low coolant level in a cross flow radiator will equalize in both tanks with engine off. With engine at running and at operating temperature, the high pressure inlet tank runs full and the low pressure outlet tank drops, resulting in cooling system aeration.
Aeration will draw air into the water pump resulting in the following:

High reading shown on the temperature gauge.
Loss of coolant flow through the heater core.
Corrosion in the cooling system.
Water pump seal may run dry, increasing the risk of premature seal failure.
Combustion gas leaks into the coolant can also cause the above problems.
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Thursday, November 10th, 2011 AT 4:31 PM
Tiny
DMARIE86
  • MEMBER
  • 6 POSTS
The mechanic gave me an answer which is blown head gasket like you said, DOH. Thanks for your help now I need to pay 1200.00 bummer!
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Thursday, November 10th, 2011 AT 4:38 PM

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