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Overheating problem 96 Grand Prix 3.1l

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Pontiacidaho

New member
So I've got a piece of **** 96 grand prix that keeps overheating. I had an Olds cutlass for about a year and a half that had the 3.1l and it had the same issues. Basically the car will run fine when it's really cold but as soon as it warms up and I start driving it, the temp gauge goes way up to 260 and it overheats. Already wasted money fixing what the issue should've been but wasn't so I'm really pissed off at this point. Head gasket is fine. No leaks. Radiator doesn't seem to have any leaks nor do any of the hoses. I put coolant in the other day to top it off. Added some in the coolant tank and the radiator. Well everytime I've put some in the coolant tank, it never sucks any back in there it just drains it. But there's no leaks anywhere on the ground. So I'm kinda at a loss. Mind you the car also has a little over 201,000 miles. And the people I bought it from were dimiwits despite being the original owners and probably should not be allowed to purchase a vehicle of any kind due to their stupidity. I replaced the coolant temp sensor because I broke the plastic top off the first one trying to pull it out. Was a ***** trying to get the new one in and it broke too and didn't get it in all the way. Fixed a loose sparkplug as well. Car is just being an asshole at this point and I've pretty much given up and am wanting to just scrap the ****er. It's also been getting extremely bad gas mileage. About 100-150 miles on a tank - if I'm lucky. Not sure why. Hasn't thrown any codes. Any suggestions? Or should I just take the car out to the gun range next time I go?
 


I will also add that if just overheated about 30 minutes ago when I attempted to drive it. As soon as I got on the freeway, the gauge started to creep up from 100 to 260 almost instantly and it overheated. Luckily I was near an exit so I was able to get it home quickly. Before replacing the coolant temp sensor, my A/C didn't work and everytime I'd turn it on, it would make a growling noise and if I'd turn it on while driving, itd make the engine sound like it was growling but knee I'd shut it off, it would stop. Also, id get hardly any air out of the vents even with the fan on high. Now when I turn the car on, the A/C is working and not making noise and the heat is working too and alot more air is coming out of the vents. I'm at a loss. Really hate having to get rides places cuz my car is a piece of **** and doesn't wanna run.
 
Yeah I really don't wanna have to take the thermostat out if I don't have to. Also last night after I got it home when it overheated, I put my hand on the radiator cap and it was cold. Normally it's really hot. I thought it was a little odd. I took it off and no coolant gushed out. I had a really similar problem with my Olds cutlass I had that had a 3.1 in it. I really don't wanna blow the head gasket because I refuse to fix that. I'm better off buying another squarebody chevy and dumping this piece of **** the first chance I get. But I can't really get to work until I fix the ****er. Is it possible the radiator cap is losing pressure?
 
I don't think so, from your description there isn't any hot coolant actually getting to the radiator and getting cooled, to then go back into the engine and cool it. When you pull the rad cap, is there nasty looking goo on the underside?

It's sounding like either a really nasty clog, or a bad/stuck shut thermostat. More often than not it's a bad tstat, and my suggestion is to take this weekend, if you don't have to work through it, bite that bullet, and replace the tstat.

While its out you can slap the intake back on and crank it over, see if it'll push coolant through the block. If it doesn't, then try the whole flushing procedure with the garden hose. If you do run into troubles, ask for help. There's plenty of people here willing to help, and I'm just one of them.
 
I appreciate the info. Unfortunately I don't have the funds to replace the thermostat. The underside of the radiator cap looks fine. It's getting the thermostat put of the housing that I'm gonna have a problem with. Could all of this be the result of bad gas mileage? Like, really bad gas mileage?
 


Maybe not the result, but it could be a side effect of the actual problem...

https://www.rockauto.com/en/catalog....1l+v6,1255980,cooling+system,thermostat,2200

You can get a new tstat for pretty damn cheap, and the original OEM one is less than $10 with shipping.

https://www.oreillyauto.com/detail/...ermostat/3899/4436249/1996/pontiac/grand-prix

O'Reillys for $6, if you want to get it now locally. You can keep these cars running for really cheap if you learn the little tips and quirks they have, and you can ask any question if you have the slightest doubt. This forum is your best friend when it comes to wrenching on a GP.

If you are really too tight on cash, just pulling the tstat out and leaving it out can probably get you back on the road until you can get the parts... I've done it myself, and I know it's not good for the engine when it can't get up to the proper operating temp, but if it gets you where you need to be... It'll have to do.
 
Yeah if i put the tstat in hot water, would that help if its stuck shut? And if the o-ring is bad, could i use something as a substitute?
 
If the Tstat is stuck, that would mean it's either corroded, or it's somehow gotten bent/broken...

If the tstat is simply stuck closed, and you manage to get it to open when it gets hot (195° is the point it's designed to open at), RTV is one way to "repair" bad o-ring and get it to seal... But it'll require a good amount of prep work for it to actually work.

Does the oil look milky? If the coolant is going into the oil, then that engine isn't long for this world, unless you really feel like a full rebuild.
 
a new t stat and gasket is like 12 bucks. flip the couch and find some change lol

if its stuck in the lim, use a screw driver in the middle V there at the top and pry it out.


and for the record, most t stats fail open, unless yours is super old, back then they could fail open or shut, shut makes it over heat.

or just take the t stat out and see if it still over heats, if it does the water pump is shot, or the rad is clogged up.
 
Well I attempted to try to get tot he thermostat to pull it out. Decided it wasnt worth it. I dont have the patience nor the proper tools or skills to do so. I'm going to check to see if the radiator is clogged. Theres not much coolant in the radiator but there was quite a bit that has dripped out. I just dont really wanna mess with it anymore.
 


Yeah I just started it up and drove it around the block. Everything was fine till I pulled it back in my driveway and then it started overheating bad. There's plenty of coolant in the radiator so not entirely sure what its doing. I have no way of getting the thermostat out unless I pull the engine and I have no way to do that either. So, any advice on what I should do?
 
For reference, the GM 3100 V6 is almost exactly the same as the GM 3400 V6, just a different displacement.

Here's your how-to for getting the tstat out: https://www.youtube.com/watch?v=ZgLWR1dCXRM

You can use a 13mm or 1/2in deep well socket, a 3in extension, and a ratchet to loosen the lower bolt for the housing. You don't have to take the bolt completely out, because the housing has a slot instead of a bolt hole, you can literally slide it up and out. Then a long big screwdriver to pry the tstat out. It's pretty easy if you go in from the top of the engine, set the tip of the screwdriver into the tip of the tstat, and give the handle a good shove towards the passenger side.

Then follow this video: https://www.youtube.com/watch?v=ad9u8jADrvU to bleed (most of) the air out of the system. Once there's no longer any big air pockets in the system, it will eventually get all of the little air pockets out just by regular driving.

If you want to try bleeding the system first, that could potentially solve this issue. Considering the mileage, age, and previous owners.... I wouldn't be surprised if it was air-locked inside the block.

After doing some research and reading myself, apparently the 3100 and 3400 V6 engines have a bad habit of developing air pockets in the cooling system.

Another video to help you out some: https://www.youtube.com/watch?v=wNHggnT9ARU&t

Hopefully one of these will help you out.
 
"Everything was fine till I pulled it back in my driveway and then it started overheating bad"

This doesn't sound right. It's over heating Suddenly?

3.1's are the worst for having air trapped in the cooling system and it requires effort to purge it.


Has the air been bled out of the system? There is a bleeder on top of the Thermostat housing. With a cold engine open the bleeder. Top off the coolant, close the bleeder. Warn the engine up, turn it off, and Carefully open the bleeder to vent steam out until coolant comes in a steadier stream.

On a cold engine,you can "milk" coolant in and air out by open bleeder, squeeze hose, close bleeder, release hose. Repeat till coolant squirts out when the hose is squeezed.


Yeah, missed WarStryker's post. So 2 votes for air in the system.
 
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I've bled the air out and done both of those methods and it still is overheating. A relative who was a city mechanic for the city of Boise for 27 years came over yesterday and put a pressure pump on the radiator and we discovered where coolant was leaking after I noticed a good amount of coolant that had leaked out on the ground. The heater core hose connector that connects into the block underneath the EGR valve, is leaking a good amount of coolant which accounts for my coolant loss and possible overheating. But, coolant is still not getting to the radiator. If it is, not much. What else could be the problem? How would I go about getting the connector off to replace it?
 
sounds like you need a water pump. they tend to have rusted out impellers.

if you remove the t stat, then take the top hose off the rad, fire it up, coolant should flow out the hose, if it dont the w/p is shot to hell for sure.
 


Scottydoggs said:
sounds like you need a water pump. they tend to have rusted out impellers.

if you remove the t stat, then take the top hose off the rad, fire it up, coolant should flow out the hose, if it dont the w/p is shot to hell for sure.
Click to expand...


Doh. Scotty got it. I had that problem on my '98 Malibu. The Blades rust off, and all you have is a throwing star spinning in coolant.
 
Yeah tried bleeding the air and still didn't fix the issue. Fixing the hose connector should be fun though. Whoever designed this engine should've been fired. I've worked on multiple gm cars, (this is my first time doing engine work on a 3.1) and never have I seen one with this ****ed up of a design. It's bull****. You pretty mech have to take the entire engine apart just to get to a simple part that needs fixed where as on any other vehicle, it's easily accessible. Just don't get it.
 
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