coolant temperature

1999 CADILLAC DEVILLE
122,000 MILES • V8 • FWD • AUTOMATIC
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MARKVELLUTATO
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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!!!
May 3, 2011 at 3:10 AM
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CARADIODOC
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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.
May 3, 2011 at 3:20 AM