1998 Pontiac Sunfire Overheating with all new cooling parts

UHCORD98

MEMBER
1998 PONTIAC SUNFIRE
4 CYL
2WD
AUTOMATIC
156,000 MILES

The car has 156,000 miles on the frame; however, it has a new motor in it with 70,000 miles on it. I bought the car with the blown motor, replaced it with a new motor only to notice once it was together and running that it would over heat. We replaced the radiator, the cooling temp sensor and have checked the compression on the head and everything tested ok, however, the car was still over heating. My determination was that the fan was coming on only when the car was in park & idling. When in drive, the fan would never come in what-so-ever. Never did know the real cause for this; however, I would like to because right now it's hard-wired to run all of the time whenever the car is on. Oh yeah, all of the relays for the cooling fan was replaced along with fuses. Thanks in advance.

2 Replies

RASMATAZ

MECHANIC
75,992 POSTS

Have you replaced the thermostat and did you bleed out the cooling system?

The computer might not be getting the input signals from the coolant temperature sensor or the temperature switch to activate the fan relay-

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Thursday, March 13th, 2008 AT 1:02 PM

ZMAME

MEMBER
5 POSTS

I know on thee cars there is a posting on blocked heater core stops flow of hot coolant too thermostat. How to solve this problem you ask? Simply drill a 1/8th hole on each side of thermostat to allow little bit of flow so the hot coolant reaches the thermostat. Or replace heater core. I also recommend getting a GM thermostat the aftermarket ones SUCK!

I have had the same problem

P.S. The reason I think it's thermostat not opening is because if your fan isn't kicking on then your rad is probably cold. There is temp sensor on the fan its self so if the rad is cold it won't turn on.

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Saturday, March 15th, 2008 AT 10:44 PM