'98 2.4L: Engine overheats in warm weather when stopped

I have a 1998 4-cyl Grand Am with around 164,000 miles on it.

When stopped or in slow-moving traffic in warm weather, the engine temperature starts to creep up. I turn the heater on full blast with the windows open, but I'm unsure if that does anything. I turn the car off and let it cool before it gets too close to overheating.

The radiator fan works and blows well.

The engine does not overheat when driving at moderate speeds (say 45+).

The cooling system got flushed recently, after this started to happen, and it still happens.

What should I look at?

Welcome to AF.

How hot does it get when idling for a long time ?

If all the air was purged from the cooling system,
then I'd start by looking at the thermostat next.
Even if its a new one it can be defective.

Also make sure it is cirulating through the radiator,
the flush could have created a blockage. :dunno:

Thanks for the welcome.

I'm not sure how hot it *would* get, but it would definitely overheat.

I picked up a new thermostat over the winter, but haven't gotten around to replacing it due to weather. I was thinking that's maybe what it is. Would it make sense to think that the thermostat wasn't opening all the way, allowing just enough coolant through to maintain temperature in colder weather or when driving at speed, but not enough when idling in hotter weather?

Where is the thermostat in this vehicle? I have the GM service manual, but it's extremely vague on just where it's located. It has an image of some sort of elbow or flange that it's situated in, but I haven't been able to actually find this part in the engine compartment!

How do I check radiator flow?

Thanks for the help.

yes it makes sense the thermostat would do this.
Thier is wax inside the thermostats copper colored part,
when it heats up it pushes the thermo valve open.
When the go bad they leak out the wax so it doesnt open or close properly.

Pretty sure its under the car on the passenger side.
If you have a GM service manual,
then it would have all the procedures to replace the thermostat.
It is by far the best to have if its the only one.

Good Luck

The thermostat is located right underneath the waterpump. To locate it and be able to get to it you'll have to jack up the car. Looking from the front of the car the lower radiator hose is on your left hand side, at the bottom of the radiator. This hose then goes underneath the engine via crushed looking metal plumbing, then goes back up on the backside of the motor. The end of the metal pipe attaches to the water pump. It should be held in by two bolts, once this pipe is moved out of the way say hello to thermostat.

Thanks for the help, guys. Turns out the water pump is located just underneath the exhaust manifold and is only accessible from above after you remove the exhaust manifold heat shield.

I couldn't find it before because it's so well hidden down there. I was feeling around with my hand til I felt a part that reminded me of the picture I saw in the service manual.

I had to remove the two top-mounted bolts holding the water pump outlet, then a single bolt underneath the car where the metal outlet pipe is bolted to a hanger on the frame. That pipe is connected to the radiator hose, so it freely swings down a bit when you remove those three bolts. Replacing the thermostat is cake as it's sitting right inside the opening.

I'm pretty sure it's fixed my problem, too. We'll see as the weather gets warmer.

Glad to hear you got it out!
They can be a pain in the butt to replace if you dont have a way to lift the car up enough to pull the pipe down.

Hope this takes care of your over heating.

If that doesn't fix your problem I'd replace the waterpump ... its possible thats your problem ... don't overheat it, the heads are known to warp & crack. The waterpump isn't fun to change, but its easier then a head ... and while its driven by the timing chain you don't have to mess with it to change the pump, once you remove the pipe & the 3 bolts on the back side of the timing chain cover it pulls straight out, GM actually made the gear for the pump part of the timing chain cover & the pump has a splined shaft that fits into the gear.

The weather has warmed up and the A/C is working great in the heat and it hasn't gotten close to overheating yet while in stopped traffic in the city.

Thanks again guys.

If that doesn't fix your problem I'd replace the waterpump ... its possible thats your problem ... don't overheat it, the heads are known to warp & crack. The waterpump isn't fun to change, but its easier then a head ... and while its driven by the timing chain you don't have to mess with it to change the pump, once you remove the pipe & the 3 bolts on the back side of the timing chain cover it pulls straight out, GM actually made the gear for the pump part of the timing chain cover & the pump has a splined shaft that fits into the gear.

the overheating problem was primarily notorios in the 2.3L SOHC models, as well as some of the earllier 2.3L DOHC models. IF it happens on a 2.4L that car was simply not taken care of and just religiously abused. There probably were a few, but in later model years it was nowhere near as prevelent as the old style 2.3L. The improvements that GM made to the coolant passages in the motor to the head have helped downplay the chances of a warped head, blown headgasket, etc.

Back to square 1.

I guess it just hadn't been hot enough for long enough for the problem to show up again, but it did.

Any tips on how to isolate this problem (water pump, clog, etc) would be appreciated.

Also can anyone tell me where the engine block coolant drain plug is on this engine? A picture of it would be super helpful too. Thanks again.

WHen the engine is warmed up feel the radiator hoses and you hsould be able to feel the coolant flowing.
If you rad. has a cap(most dont) you can look in it while its running to see if you have coolant flowing.

Not certain onthat block drain but usually its on the back side of the motor.

You might try a cooling system flush with a couple bottles of flush treatment. Then drain rinse several times and refill with the correct amount of coolant.
At least 50/50 - water/coolant mix.

WHen the engine is warmed up feel the radiator hoses and you hsould be able to feel the coolant flowing.
If you rad. has a cap(most dont) you can look in it while its running to see if you have coolant flowing.

Not certain onthat block drain but usually its on the back side of the motor.

You might try a cooling system flush with a couple bottles of flush treatment. Then drain rinse several times and refill with the correct amount of coolant.
At least 50/50 - water/coolant mix.
Which hose do you mean, specifically? There is a hose on the passenger side, underneath that attaches to a crushed metal pipe that goes up to the water pump. I believe this is the outlet hose.

There's another large hose that goes from the driver's side of the engine to the radiator, I think this is the inlet pipe.

I assume either would work. Should these hoses feel firm/pressurized when the engine is cold or hot? I know the outlet hose feels somewhat empty when the car is off and the engine is cold.

Should one feel hotter than the other? Same temperature? Feel them when the engine is warm/hot/cold?

Sorry for the questions, but I just want to know what exactly what I should be feeling.

Upper hose, which is also the outlet hose is the one on the drive's side. Inlet hose is on the passenger side, and the way the system works is coolant circulates through the head, block and heater core. Looking at the heater hoses, there is a plastic coupling through the center of the hose assembly. This is a bypass so if your heater core clogs the thermostat will still open and close. Check your heater hoses, see if they have collapsed, or if they have been replaced with straight hoses. My 95 did the same thing, ran warm (210) when driving in traffic, and at a normal temp on the highway (180). The reason for this is the waterpump creates enough pressure to partially force the thermostat open at higher rpm's. It's a system that works great when it works, and when there is a problem it's a real pain to find.

Upper hose, which is also the outlet hose is the one on the drive's side. Inlet hose is on the passenger side, and the way the system works is coolant circulates through the head, block and heater core. Looking at the heater hoses, there is a plastic coupling through the center of the hose assembly. This is a bypass so if your heater core clogs the thermostat will still open and close. Check your heater hoses, see if they have collapsed, or if they have been replaced with straight hoses. My 95 did the same thing, ran warm (210) when driving in traffic, and at a normal temp on the highway (180). The reason for this is the waterpump creates enough pressure to partially force the thermostat open at higher rpm's. It's a system that works great when it works, and when there is a problem it's a real pain to find.
The thermostat is new and revving the engine does not alleviate the problem, whereas speeding up to 50 mph almost immediately makes the temperature start going down.

Thanks for getin those details skibum! :thumbsup:

I know these systems are not the best and dreadfull to find any blockages/problems, which it sounds like you might have jonnythan.

Not a problem. I think I dealt with just about every problem that could happen with a quad in the time I had mine. As for this one, definately sounds like either air in the system or something is blocked, or quite possibly a bad water pump. What condition was the coolant in when this all started?

This started some time ago. I did not see the coolant come out when I got it changed at Valvoline, but the coolant in the reservoir looked OK.

It was pretty old by then. About 125,000 miles and 7 years or so.

I'm going to try a couple of flushes with cleaner.

When I replaced the thermostat, I ran the engine for quite a while with the reservoir cap off to try to get the air out of the system. Three or four times, the coolant surged and then bubbled and then got sucked away. I assumed this was air leaving the system and I refilled the reservoir each time it all got sucked away.

Sounds like your radiator might have a partial blockage in it as well.

That's what I'm thinking between reading this thread and another thread I have going on another forum.

I'm going to put in some Prestone Super Radiator Cleaner tonight then drain it out tomorrow evening and see where we are.

Thanks again for your help.

OK, after a couple bottles of radiator cleaner it seems a *little* better. With the A/C going and idling in 90+ degree weather, it got only slightly above the normal range, but still a fair bit away from the red. I guess there's a bit of a clog somewhere. Oh well, as long as it's not overheating..

I actually solved the problem completely while servicing my A/C.

I had to replace the condenser because it had a small leak. When I took the condenser off, the radiator had a nice big perfect circle completely clogged with dust, dirt and gravel.

The fins on the radiator are significantly smaller and narrower than the fins on the condenser. I suppose lots of stuff passed right through the condenser fins and got clogged in the radiator.

A hose and some Simple Green cleared it right up.