Overheating: Pontiac Sunfire

Tiny
KIVAR34
  • MEMBER
  • 1998 PONTIAC SUNFIRE
  • 4 CYL
  • 120,000 MILES
Two days ago my girlfriend was driving my 98' Pontiac Sunfire and said that the car was heating up past the 3/4 mark.

I took the car out yesterday (20min drive) and it started reaching the 200degree mark. Finally I turned around to go home and the car started overheating. I stopped and parked the car. Steam was coming out of the antifreeze reservoir and antifreeze poured from the cap.

I decided NOT to run the car after that and the car was fine. I drove it for another 30min and even kept it idling after and it was fine.

I drove it again and about 15min into the drive it started heating up. The car went into overheat. On the drive home it was fine. Now it is running hot again.

I haven't drove it since and have topped off antifreeze.

What is possible causing this problem?

Fans work.
Antifreeze seems to be flowing as when I refill it goes down.
No signs of leaks other than when it overheats.
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Monday, December 13th, 2010 AT 6:44 PM

8 Replies

Tiny
CARADIODOC
  • EXPERT
Have a mechanic check for combustion gases in the cooling system. A positive test indicates a leaking head gasket. The tester has a special dark blue liquid that will turn bright yellow in the presence of combustion gases.

Caradiooc
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Monday, December 13th, 2010 AT 7:00 PM
Tiny
KIVAR34
  • MEMBER
Is it possible that it is the themostat? Steam only comes from the antifreeze tank and not the rest of the car.
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Monday, December 13th, 2010 AT 7:55 PM
Tiny
CARADIODOC
  • EXPERT
Typically thermostats stick open so the engine doesn't reach normal operating temperature. They rarely stick closed. If it did, you would not be adding coolant to the system. What CAN happen is the combustion gases getting into the cooling system can prevent the thermostat from opening if an air bubble collects under it. Hot air will not cause a thermostat to open. The sensing pellet must be hit with hot liquid.

This is confusing:

"I decided NOT to run the car after that and the car was fine. I drove it for another 30min".

Part of your observations suggests an inoperative fan but you said it's working. If it were a fan problem, the engine would not run hot at highway speeds. If this is indeed a head gasket problem, when it gets bad enough, you will see large bubbles in the reservoir shortly after starting the engine, and before it has time to get warm. It will look like the coolant is boiling but it won't be hot yet.

Caradiodoc
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Monday, December 13th, 2010 AT 8:09 PM
Tiny
KIVAR34
  • MEMBER
I meant to say:

I decided Not to run the HEAT after that.

I have not seen bubbles, and the fan turns on when starting.
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Monday, December 13th, 2010 AT 8:12 PM
Tiny
KIVAR34
  • MEMBER
The heat has also not been used since last March.
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Monday, December 13th, 2010 AT 8:16 PM
Tiny
KIVAR34
  • MEMBER
I also have not seen the fan turning when the car is hot. But again the car should not overheat on the highway so I did not focus on the fan.

The problem seems like it could have originated with the heating system.
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Monday, December 13th, 2010 AT 8:18 PM
Tiny
CARADIODOC
  • EXPERT
If the engine really is overheating, feel the air temperature from the heater. If it is real hot, the heater core is fine. Suspect poor circulation through the radiator. A loose or corroded water pump impeller always comes to mind as well as a plugged radiator, but a less known problem, especially if you live in a state where they throw a ton of salt onto an ounce of snow, is rotted cooling fins between the radiator tubes. That WILL lead to running hot on the highway because the radiator can't give up its heat. The heater will work great, in fact running the heater on high will bring the engine temperature down rather quickly.

Some GM engines need coolant to circulate through the heater core to get to the thermostat and cause it to open. In those, a plugged heater core can lead to overheating. The clue is when the engine is hot, the air from the heater will be cool.

None of this applies if you're adding coolant on a regular basis. If you don't see any leaks, you can add a small bottle of dye, then check various places with a black light. A common place to look is the tail pipe. If you find dye there, you will most often see white smoke too while the engine is running. That would be another sign of a leaking head gasket.

Caradiodoc
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Monday, December 13th, 2010 AT 9:25 PM
Tiny
KIVAR34
  • MEMBER
For anyone on this board with a similar problem, here is what was happening and the fix.

Noticing that the antifreeze was only pouring out of the radiator cap at the antifreeze reservoir. I decided to change the radiator cap. When I put on the new cap it felt as though it was tighter. The car has now run completely normal and the temp. Never rises past midway through the gauge.

The reason this has begun to happen now is because the heat hasn't been turned on since last March. Running the antifreeze through the heating system has caused an increased drop in pressure.

Thanks for your help.
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Wednesday, December 15th, 2010 AT 8:56 PM

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