: Cadillac De Ville 1999 OverHeat

06-01-08, 12:35 PM
I had a Cadillac De ville 1999 northstar engine 4.6Ltr the car was fine until one week back starts to make overheat on driving only on idle no overheat at all even if you put the A/C On Or the Heater On no Over Heat At all Put If you Drive it for 5 miles on the highway the temp go to 257 F on idle its always 205 to 222 F on the highway more than that and this what i did

I just had the engine flushed , water pump, radiator, and i changed the temp sensor, and the radiator cap, and alternator replaced relays of the fans and the two fans, thermostat, i did a head gasket check and those were fine. we took the air pockets out from the radiator. and we installed new extra fan to cools the engine, and we checked the engine oil its fine no water and clean and the radiator no oil and no smoke coming out from the car and no miss firing and the engine noise is like new you can't till that the car is running.
and transmission oil is ok no any kind of leak in the car
and The car still only starts to overheat when you drive it. It does not overheat when it is idling and you just sit there. What else could it be????

06-01-08, 12:50 PM
Did you use a chemical test kit to determine if the coolant has exhaust gas present? This test is best performed after any new coolant has had a chance to "settle in" and absorb any foreign chemicals, if any.

Considering the amount of work and replacement of parts, your description is classic Northstar headgasket leakage due to head bolt tension loss.

06-01-08, 04:13 PM
How did you "take the air pockets out"? There should be none as the Northstar is self purging. Do a search for purge line and make sure it is clear.