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2000 Cadillac Seville STS overheating problem: After warm-up, stays around 2 ticks before H. Rarely, hot air blowing from heater core. Need help!

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I live in Hawaii and just bought my very first Cadillac for $600 with about 83K miles on it from the Honolulu airport area. Just needed a temporary car to get me to work and back. The person selling the car said it just needed some fixing but runs fine. His friend gave it to him because he had to move to the mainland. The seller's reason for selling was he had no space to store the vehicle. The car was selling for around $1000 at first then drop to $600 because the "engine got hot but not overheated". With the help of family members, we tried to get it over the Likelike Highway which is a reasonably difficult hill. However, the car never made it there because it overheated. We did try to keep topping it off with an all-vehicle Preston yellow container green coolant but no good. We ended up towing it to my living location where it would sit until it could be sent to the mechanic shop. 

Current Mechanic Coolant System Fixes and Replacements:

-The old thermostat was cleaned but not replaced.

-New radiator and radiator fans installed.

March 13th-14th, 2023 Test-Run Analysis: When I picked it up on the 13th of March from the mechanic shop, they said to drive it for a few days and then let them know. They said it stayed around the 2nd tick from the 12 o'clock position but didn't go to H anymore. Drove it around in the afternoon for about 45min trying to see how well it now handles. Stay around the two ticks from the H but only once went over. Parked it at home and let it sit for a bit. Went back out at night to see if it would make a difference with the cool night air. The hot air actually kicked on for a little bit and the temperature gauge stayed at the 12 o'clock position. However, it didn't last too long before it went back to cool and the temperature gauge went back to two ticks from H. Barely made it home because it was going over but didn't go to the red zone. I'm thinking about replacing the thermostat and water pump myself to see if that fixes the problem. 

Current Condition of Vehicle for Possible Clues: Suspecting possible accident from the front. The left headlight is newer and not fitted in properly as the right headlight is. The blinkers just stay a solid yellow when turned on. The hood looks like a replacement sprayed over incompletely to match the color but with no clear coat. The front bumper is pointing slightly down with a small cracked hole on the side of the bumper. ABS, Traction Control, and Airbag lights stay on. The new radiator doesn't fit properly on its left mounting side piece. No coolant flush yet just been topped off after some parts were replaced or cleaned. I hope this also helps in some way or form. 


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Couple of pics added.....

Gauge...not sure how accurate the description is....but likely pretty close. Gauge should stay at 12 o'clock. 

Front air baffles. Often damaged in front wrecks. Large lower panel and 2 side air baffles are needed or you can have overheating problems. # 4, 5, 6 and 15. 

Fans. Both should turn freely turned off....may be jammed or broken or missing. A real good scan tool can turn on/off the fans for testing (GM Tech2). This also verifies wiring, relays and fuses. 

Could have possible wire harness damage, blown fuses or blown fuse links. 

The Northstar is also known for pulled head bolts that causes overheating. But....being the car appears to have past front end damage....I would check all that before chasing head bolt issues. 






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Check the water pump belt. You would be surprised how many mechanics do not know it is on the driver side. The pulley and or tensioner can seize up and break the belt or not put enough tension on the belt. Does the car overheat when idling? Or only when driving?

Sometimes the water pump can seize, but rarely have I seen it happen. Located at the driver side of the engine, Can see the tensioner between the radiator fans and the engine. On mine it is right by the torque strut

Trying not to be suspicious of head bolts until I know more. But the more it overheats the more a chance that will/has happened.

When it overheats I assume it boils over?


Nice, clean, luxury= fine automobile

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