Overheating issue

Tiny
LLOYD O'CONNELL
  • MEMBER
  • 2002 CADILLAC DEVILLE
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 169,195 MILES
The coolant overflows out of expansion tank when heater is shut off and remains calm when heater is on. Why would this be?
Saturday, September 7th, 2019 AT 12:31 PM

1 Reply

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Hi

I would suggest starting with checking the thermostat. You can remove it and put it in a pot of water and put it on the stove. The thermostat should open when the water gets to about 180 degrees.

Usually, when the engine doesn't over heat when the heat is on, it is because the thermostat is not opening fully causing a restriction or the coolant level is low causing air pockets.

Turning the heat on is blowing more air over the coolant when it goes through the heater core in the HVAC so it dissipates the heat more. Again, I suspect the thermostat is your issue.

Let me know what you find and we can go from there. Thanks
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Sunday, September 8th, 2019 AT 11:27 AM

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