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Hello Everyone,


So i am having an issue with my 2007 Cadillac DTS.

The engine is running extremely hot, however the temp gauge is reading normal. Coolant Reservoir boils and smokes with cap off, and leaks with cap on due to too much pressure.

Fans are not kicking on.

Block test came back negative for blown head gasket, but the coolant reservoir was so hot it warped the plastic on the block tester.

What would be the next culprit to look into??


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First thing that comes to mind is a defective coolant temperature sensor. Second thing is a defective pressure cap. Third thing is a plugged or restricted bleed line to the coolant recovery reservoir. Fourth thing is a stuck or only partially opened thermostat. Fifth thing is faulty cooling fan relay. Sixth thing is very low coolant level in the engine ( the coolant sensor HAS to be submersed in coolant, it will NOT give an accurate temp reading if it is surrounded by air ).

Seventh thing is any combination of the above.

Check the coolant level FIRST. ( Be sure to use Dex-Cool coolant and drinkable or distilled water to a 50-50 solution.) Check it with the engine cold not running, fill it within 2-3 inches of the top of the recovery reservoir. start the engine and let it run for 5-10 mins with the recovery reservoir cap OFF, or less if it starts to boil over. Shut the engine off and let it cool for 20-30 mins and repeat the process if necessary. The engine holds about 2 gals of the 50-50 mix. I would plan on replacing the reservoir cap regardless, so when the engine coolant level is correct and the level does not drop after the cool-down period, install the new cap and retest to see if it still overheats.

Any repairs / work done to the engine recently? Does the temp gage start cold and climb to normal or does it start at normal operating temp when you first start the engine?

You will need a scan tool to see what coolant temperature the computer is seeing.


Edited by OldCadTech


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