You are here:

Pontiac/1998 Sunfire Overheating


brad wrote at 2008-03-16 21:38:24
Good answer however its wrong. My daughter also has a 98 sunfire 150000 km with the same symptoms.I changed the thermostat twice and eventually took it right out. It no longer overheats of course but it still looses fluid around the cap. This is definitely a head gasket problem.

Ice G wrote at 2008-09-20 23:50:43
It does sound like the head gasket is gone, reason said is that i had a 1997 Honda Civic that did the exact same thing. Cost me $750.00 later

Keith wrote at 2010-12-24 18:10:48
I spent a great deal of time on my son's Sunfire with the same problem. I even put the old thermostat in boiling water and it opened at the right temp. I found a few things that must be done. One is you must fill the overflow bottle with the bleeder screw open until all air is gone. Two change the thermostat with a high quality unit. The cheap crap from China is a waste of time. Three clean out the area where the thermostat mounts. I think this causes the thermostat to stick at times. I did these three things and it finally fixed the issue. I was baffled for days.  

ManWithNoName wrote at 2011-01-31 04:25:09
I have your fix. Your Heater Core is plugged. Disconnect your Heater Core hoses and flush the heater core or replace it. The coolant has to pass through the heater core before it gets to the Thermostat. GM came up with this design to speed up in-cab heating.

Chris wrote at 2011-07-01 21:18:17
I have a 98 Pontiac Sunfire with the 2.2L as well. I read your message and I have the same problems. I changed the water pump, thermostat, and radiator cap. I filled the coolant up after that. The coolant is coming out the radiator cap due to the pressure. The coolant is boiling in the reservoir and spilling out while driving when it is overheating. This happens here and their. My mechanic checked it out and ran some tests. He got it to overheat and pulled the radiator cap after releasing the pressure. Every minute or so under certain conditions with hitting the throttle a bubble would surface from the bottom of the reservoir tank. My mechanic said its the head gasket for sure in its early stage. He said the bubble is from the combustion or the exhaust leaking into the coolant system. His recommendation for temporary fix was coolant seal. Ultimately the head gasket needs replaced. Hope this was helpful.

ryan wrote at 2012-02-13 18:28:04
another problem may be you have an air pocket i also have the same car and i changed the lower radiator hose and afterwards the car ran hot so take your radiator cap off and let the car heat up for about 15 min and watch the coolant level, the heat will force out the air and everything should work fine  

Hannah's Dad wrote at 2012-10-07 19:42:20
Believe it or not, the overheating problem may be cause by the Power Train Control Module.  What you say.  OK the ground for the fan motor goes thru a relay whose ground is through the power train control module.  As the temperature sensor reaches the minimum temperature for the fan to kick in a ground is applied to the relay (not the power, so it is hot all the time, key or no key).  If you were to check for a ground continuity with a volt meter, it may indeed show a ground, but if you apply any load, such as a relay, it opens up, or does not provide a path for the current (check it with the amp meter).  GM had a recall for the PTCM for the cars in the north east due to salt infiltration from road salting, this was to put a cover over the module.  Right not I have bypassed the ground with a manual ground I switch on from inside the car one I start it up. I've been chasing this problem for a while and have to replace a radiator because of it.

Jen wrote at 2013-02-13 04:42:35
I am having same problem haven't replaced head gasket yet did thermostat first still having prob now think may be air locked what do I do??


All Answers

Ask Experts




20 year GM dealership Technician. ASE Master Tech. Can answer any major or minor system questions


20 year GM master tech

©2017 All rights reserved.