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Coolant temperature

Tiny
MARKVELLUTATO
  • MEMBER
  • 1999 CADILLAC DEVILLE
  • V8
  • FWD
  • AUTOMATIC
  • 122,000 MILES
I have a 1999 Cadillac Deville. It has a digital coolant temperature reading on the dash and it runs perfectly at about 190 degrees. However, if I sit at a long red light or just creep along in a traffic jam, the coolant temperature will go as high as 220 degrees. Is this a problem? How high can the coolant temperature get before I need to worry that I have a problem? I don't want to blow a head gasket and have a major repair!
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Tuesday, May 3rd, 2011 AT 3:10 AM

1 Reply

Tiny
CARADIODOC
  • MECHANIC
  • 33,864 POSTS
GM engines do hit 220 degrees at times. Water boils at 212 degrees but that increases three degrees for every pound of pressure on the system. That's why we use a 15 psi pressure cap.

What's more important is whether the fan is working properly. Electric fans should be running by around 212 degrees. Belt-driven fans typically use a thermostatic clutch that can fail and let the fan free-wheel. The clue to a fan problem, as you noticed, is the temperature comes down when the car is moving faster and there is more air flow.
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Tuesday, May 3rd, 2011 AT 3:20 AM

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