1996 Pontiac Grand Prix GTP 3.4L randomly overheats

Hello all! I’m new to the forums but not new to the show, my dad and I have listened to it for several years. Anyway, I have a problem with my car that I was hoping someone could help me with.

As the title states I own a '96 Grand Prix GTP with the 3.4L engine. I had been having a problem with my coolant leaking so I took it in to a shop I usually trust, they pressurized the system and found my water pump was leaking. Not surprising, I had suspected it was having issues. So they replaced it and all was good for about a day or two. I live about 5 - 10 minutes from work and as soon as I drove it longer than that, it started overheating at random intervals. I took it back in and they told me it was probably my head gasket but they couldn’t see any visible evidence of it going bad so they said it must be in the early stages. I was not satisfied, I hadn’t had any problem until after the water pump was replaced and I’ve never had any major engine issues. I finally managed to nail down a sort of pattern to the overheating. It only starts to overheat once it has been running for awhile, whenever it does overheat neither of my radiator fans turn on, turning to the right while driving cools it down, turning it to the left while driving allows it to overheat again, revving the engine when it overheats ALWAYS cools it back down at least for awhile. The other strange thing is that it will overheat for awhile and then stop and go back to normal operation, my fans will work again, and the temperature never climbs past 210. Then at another random interval, it will start overheating again.

Can anyone help me out? It doesn’t sound like a head gasket going bad to me but then I’ve never had one go out on me. It sounds more like I have a coolant flow problem (maybe the new water pump is faulty?) because every time I rev it, it cools down immediately. Or maybe I have a faulty sensor/thermostat/computer module since my fans never run when it overheats and it never overheats when my fans actually turn on? If it’s a head gasket I’ll deal with it but at this point I am a little skeptical. Does anyone have any ideas/advice? Thank you!

Start simple clean and check the connections to the fans.


I doubt your head gaskets are leaking. More likely, it’s the intake gaskets. Fairly common on your engine. Check this out.




The OP’s car has the DOHC 3.4L not the OHV 3.4L. The LQ1’s didn’t have the same intake gasket problems IIRC.


I did some “research” . . . and you’re correct

OP’s engine seems to be a fairly complicated setup, as are all ohc engines which are derived from ohv designs . . . the Ford 4.0 OHC V6 comes to mind


Yes, the DOHC 3.4L has a reputation for being incredibly difficult to work on, even by transversely mounted engine standards. I have a friend who bought a 1992 Grand Prix new 20 years ago, the dealership was trying to get her to buy the GTP model, but she ended up with the more basic SE model with the 3.1L. Ended up saving her thousands in maintenance costs.

Ah, your friend did NOT buy a car and so now you know what the repair costs MIGHT have been?

No it’s just common knowledge amongst car enthusiasts that the GM 3.4L DOHC is a nightmare to work on. Consequently the labor rate ( in terms of hours per job) is higher than average. The timing belt is a $800 (or more job) and it needs to be replaced every 60k miles. The 3.1L OHV uses a timing chain which ordinarily doesn’t need to bee replaced. So just that alone will save you thousands on maintenance.

hello gearhead i have a 1996 pontiac grand prix gtp w/ 3.4l and i had the same problem after changing my water pump and i was able figure out what it was after replacing the temp sensor and it still did the same thing. the temp would rise quickly and them within 2 seconds it would drop back to normal and then repeat. it turned out to be that air would get trapped under the temp sensor making it seem like my car was overheating but the car ran fine i fixed it by opening the radiator when the car was cooled then letting it run with the cap off and turning on the heat full blast ( you have to turn on the heat or else air stays traped in your heater core) keep the car running at around 1200 rpm’s to push the air out and make sure to top your radiator off with coolant, once your fans turn on put the cap back on while the car is running after that your good to go. cheers

true, some motors are trouble prone. you can probably lump the 3.4 ohc motor with the 3.5 shortstar motor. not GM’s best efforts.

Thanks everyone for all the advice! I really appreciate it. Yes, my engine is a nightmare to work on. I do most of my own repair and maintenance myself and it is very difficult to get at anything. grimace


That is exactly what my car is doing and right after changing the water pump as well! I will take your advice and try that out ASAP and let you know how it goes. It’s nice to hear that someone else has the same year and model car, all my searching around on forums and online it seems like no one else but me has this kind of car anymore and trying to find info on problems or repairs is difficult. Thanks again!