1998 Grand Am SE Diagnosing a cooling problem

I have a 1998 Grand Am SE 2.4L

The problem is that in hot weather city driving, the coolant temperature will slowly increase to above the "normal" range on the temperature gauge, at which point I will shut off the engine and let it cool to avoid overheating. Highway driving, even in hot weather, makes the temperature stay pegged at its normal spot (constant temperature) or return to that spot after having been doing city driving.

I have had the cooling system flushed at Valvoline.

I have replaced the thermostat with a 180-degree model from Stant.

The radiator fan turns on and off as appropriate and appears to me to blow sufficient air.

The radiator grill does not appear to be clogged by debris.


I suspect some sort of coolant flow problem, since I'm not sure what else it could be. Perhaps the water pump, or a partial clog somewhere in the system is the culprit.

My question is how to diagnose where this problem lies. I don't want to throw parts (like a water pump or radiator) at the problem.

Thanks. Try this. Turn off the AC and let the engine run in your driveway. Watch for the coolant fans to come on. It may take a while before the engine gets hot enough for the fans to come on. Then watch to see if the fans shut off. If they shut off then your engine isn't overheated. If they stay on and your gauge is getting into the red then you have a problem. Take note on your gauge when the fans come on and go off. Then turn on the AC and watch the gauge. It should stay normal. discretesignals wrote:Try this. Turn off the AC and let the engine run in your driveway. Watch for the coolant fans to come on. It may take a while before the engine gets hot enough for the fans to come on. Then watch to see if the fans shut off. If they shut off then your engine isn't overheated. If they stay on and your gauge is getting into the red then you have a problem. Take note on your gauge when the fans come on and go off. Then turn on the AC and watch the gauge. It should stay normal.

I'm pretty sure the fan stays on and the temperature still goes up, but I'm not 100% on that.

Why would the fan go off if the temperature gauge is almost in the red zone? Are they controlled by separate sensors or circuits? This is intriguing to me. The fan is controlled by the Engine Fan Thermostat, while the temp. guage is controlled by the Engine Coolant Temp. (ECT) sensor located by the thermostat housing.

If the fan kicks on and off while running, then the ECT sensor is most likely bad. $7-15?

You changed the thermostat properly...

Your upper radiator hose will stay cool until the thermostat opens and the water pump circulates the coolant. If the hose gets hot suddenly when your gauge reaches temperature, I would feel confident the water pump is working. You can feel a surge.

If your fan stays on while running and gauge is way above normal, it is possible you have a hairline crack in the head gasket between the piston and coolant channel. Best test is a compression check. Other tell tale signs (engine running)...moisture coming out exhaust when you hold your hand there... radiator cap off, you will notice bubbles coming to the top of the radiator.

2.4L with miles on them are popular for this. If you change the head gasket, make sure you have the head resurfaced and machined by a shop as the aluminum head warps when removed. Head bolt sequence and torque is mandatory. Engine fan thermostat?

I can't find any reference to anything called that in Mitchell or my GM service manual.

There is also no radiator cap and I am not losing coolant. I looked it up on the AutoZone.com website. It calls it a Cooling Fan Control.

Not familiar with your year, but basically electric fans are simple.

You have the fan motor, a sensor that monitors coolant temp, and a fan relay.
Gauge has sensor and gauge itself.
Most cars have seperate sensors.
Some vehicles share the same sensor. 2 wires no, 3 wires yes.

The small wires of the sensor energizes the relay which connects the bigger wires to energize the fan motor.

The sensor can be mounted on the radiator or thermostat housing or even the intake manifold beside the thermostat housing.

Okay, you have a closed radiator. It should still have an overflow hose going to a coolant reservoir. You would notice bubbles there if it was the head gasket.

Is the vehicle actually overheating or just a defective ECT. Need to find this out first. Coolant fan operation is controlled by the PCM(Powertrain control module or brainbox). The PCM monitors the ECT sensor. When the coolant temperature reaches a predetermined temp the PCM ground the relays that turn the coolant fans on. The PCM also turns on the coolants fans when the AC has been requested. Usually if an ECT sensor goes bad, the PCM will keep the coolant fans on regardless of engine temperature. It will also turn on the check engine light and set an ECT code. I don't think that the ECT is your problem.

I have never seen a headgasket on Quad 4 blow out in all my time working at two GM dealership and the independent shop I am working at currently. I don't think they were common for headgasket issues. Greasemonkey you are probably getting confused with the 2.2L. Quads did have a problem with waterpumps leaking externally. You would notice leaks from the backside of the engine if the waterpump was leaking.

If the waterpump wasn't pumping water, the engine would overheat no matter how fast you drive plus your heater wouldn't work.

The fans should not go off if the temp gauge is in the red zone. They should stay on cause the engine is in the process of overheating. The fans should come and and go off before you get to that area on your gauge. If the fans cycle on and off, then your engine isn't overheating. If you have the AC on does the engine get high up on the gauge?

When you have the AC on the fans stay continously on no matter the coolant temperature. Since the fans stay on all the time with the AC on, the coolant temperature will be around the thermostats opening and closing temperature rating.

If you notice that it is overheating with the AC off and the coolant fans are not cycling, then turn on the heater full blast and watch the gauge. If the gauge drops big time then you have a clogged radiator. discretesignals wrote:Coolant fan operation is controlled by the PCM(Powertrain control module or brainbox). The PCM monitors the ECT sensor. When the coolant temperature reaches a predetermined temp the PCM ground the relays that turn the coolant fans on. The PCM also turns on the coolants fans when the AC has been requested. Usually if an ECT sensor goes bad, the PCM will keep the coolant fans on regardless of engine temperature. It will also turn on the check engine light and set an ECT code. I don't think that the ECT is your problem.

That was my thought too as well. I was under the impression after reading the manual that the ECT was the only sensor involved, and since the gauge appears to work and the fan certainly comes on when it nears the upper end of the normal range, I figured the ECT was OK.

discretesignals wrote:The fans should not go off if the temp gauge is in the red zone. They should stay on cause the engine is in the process of overheating. The fans should come and and go off before you get to that area on your gauge. If the fans cycle on and off, then your engine isn't overheating. If you have the AC on does the engine get high up on the gauge?

I don't know. I've been having AC problems (now resolved, I think) and every time in recent memory this has happened I know the AC has been off.

discretesignals wrote:If you notice that it is overheating with the AC off and the coolant fans are not cycling, then turn on the heater full blast and watch the gauge. If the gauge drops big time then you have a clogged radiator.

That's also what I'm figuring. The whole separate sensors thing was throwing me for a loop. I do think it's really odd that a 10 degree difference in ambient temperature can mean the difference between "upper normal" temperature and "I have to shut it off before it overheats" which looks to be at least 20-30 degrees higher.

I picked up two bottles of Prestone Radiator Cleaner and will run that through. My only hangup is that I have no idea where the engine block drain plug is (curiously, the GM service manual gives no hints) so I'll only be draining from the radiator. I hope that's OK.

Thanks to all of you for all of your help. It's greatly appreciated. Can anyone tell me where the engine block coolant drain plug is on this car? Or at least how to identify it?

The GM service manual and Mitchell do not indicate where it is or what it looks like. 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.

When the temperature gauge is in the upper end of the normal range, the fan comes on and it stays on regardless of the A/C.

Oh well, as long as it's not overheating, especially while using the A/C, I guess I'm OK.

Never found the engine block drain plug, though. sorry...looks like it is on the back side...goodluck...P.S I think the picture is upside down...lol

Thanks for the image. I finally did find it in the GM service manual. It was in the chapter about dismantling the engine block and is never mentioned in the section about the cooling system! Go figure.

It was pretty difficult to figure out the orientation of that image with the engine installed... and as best I can figure the plug sits right below the exhaust manifold in a spot I'd never be able to reach well. Seems like it worked out anyway.. just an extra round of "drive it so it circulates, let it cool, drain, fill"

The arrow is probably pointing to the front of the engine which would be facing towards the right side of the vehicle. I think it is upside down because you can see the crank journals and oil pan rails are facing up. You are probably correct about it being on the side where the exhaust manifold is. It probably is a pain to get to cause the transaxle sits right behind the oil pan. 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 almost 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.