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3100 SFI V6 Overheating (Coolant System) (1994-1999)

b d0ubles
12-03-2003, 11:41 AM
I have a well maintained 1995 Grand Prix SE coupe with the 3100 SFI V6. It has about 112,000 miles on it and the engine runs quiet, smooth, peppy and feels just like new. I've had the car since 77,000 miles and i have had very little wrong with it until out of no where I was experiencing overheating on several occasions. First, i replaced the thermostat and it still over heated. Then I checked my coolant and noticed it was very low. I found that my intake gaskets were leaking (common problem on 3100's). So I took apart the top half of the engine and replaced them flawlessly. Everything was normal for 2 monthes. No more coolant loss and the car was running cool then it sarted overheating again. I checked both fans and they worked but I noticed that when the car's temp was in the red the coolant hoses were ice cold. This means there was no circulation in the coolant system. I thought maybe a faulty thermostat... nope. I turned on the car and let it run until it was in the red and I opened the 2 coolant bleeder valves. My worst fear was confirmed when massive amounts of air blew out of the coolant system and the coolant started flowing again. I didn't want to believe it was a bad head gasket after all the work i just did replacing the intake gaskets so i drove it and it overheated 3 weeks later. I bled it again and it runs fine right now but obviously this is not going to stop. Air is somehow getting into the coolant system causing an air bubble blockage which is stopping the coolant from flowing. I took the Prix to the pontiac dealership and they did a head gasket test on it. THE CAR FAILED!!! Ouch, now all that work I did must be torn apart again in order to dig my way down to the head gaskets at the center of the engine. I'm about to start the head gasket job in a couple of hours today (12/3/03). I'm going to need to send out the head for inspection of cracks and I will have all my valves and valve seals cleaned up and reconditioned since its apart. This has gotta be the final step in fixing my coolant system, and if it overheats again after this I'm screwed because I have to drive the Grand Prix half way across the country next month. If anybody has simialr problems let me know. I'd like to find out if i'm doing the right thing or just wasting money. I hope this will help some of you 3.1 fans out there.

11-27-2005, 11:37 AM
I would not replace your head gasket, GM made the 3100 out of a semi aluminum block which they thought would help weight but when this engine overheats, because it is partially aluminum it ruins the bottom end of the car aswell and i guarantee you your cylinders are worn and you are probably leaking coolant and oil out of your exhaust. Run your car and see if you have any fluid or oil leaking from your exhaust. A bad sign will be if your exhaust seems to be whiter than normal. You will pay 500 bucks to get your headgaskets shaved and you can purchase a refurbished engine for that...Thats what i did, because i had the same problem you did. I found your forum and was wondering if i didnt write that myself because our problems are so similar! If you want to do a motor swap you can do an SFI 3800 V6 Turbo Just be sure to run a good intercooler and rework your cooling system

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