Overheating

[moliva1568]

The temp gauge on my 98 Cavalier creeps up close to red when in traffic or stop and go driving. it seemed to be only doing it during the day but today it did it at night. it does go down once i get moving. i changed the thermostat and it doesn't seem to have helped. it actually seems like it's doing it more now. there's no leak from what i can see, the coolant tank is full and i hear the fan come on. where should i turn my attention to now? thank you

[shorod]

You should make sure that the fan is actually moving air. You might also check the radiator and/or A/C condensor for debris. Maybe the flow through the radiator is restricted. You could try spraying water from a garden hose from the engine compartment to the front of the car to clear out debris.

Also, if you have access to a cooling system pressure cap tester, you should verify the cap is able to allow the proper cooling system pressure, or just go ahead and replace the cap.

Since you had the system open to change the thermostat, are you sure the cooling system is still full of coolant? Does the level in the tank change between cold and at temp? There could have been an air pocket in there. Check the level.

-Rod

[moliva1568]

the tank is at the full cold line. when i changed the thermostat i ran the car without the cap to get any air out as per the manual. visually looking at where i pour the coolant in, it doesn't appear that it's any lower when the car is at normal operating temp. before i turned the car on, if i squeezed the upper radiator hose you could hear liquid and see in the resevoir the coolant going up an down a little. when the car is on and running, the hose is hot, much harder to squeeze and i don't really hear or feel any fluid like when it was cold.

the fan still kicks on and blows with some good force. i haven't tried the garden hose idea yet. things i have been reading mention possible head gasket problems. is there something i should look for that may be indicitive of that? on a side note, my blower motor doesn't work and neither does the AC. not sure if that's really relevant. The AC worked when i got it last summer but the hose leaked all the refrigerant and i've yet to fix it. the blower motor went out a few months ago and i didn't change it because we where just approaching summer and the heat wasn't really necessary.

some say take out thermostat and see what happens. i really don't want to waste the $30 worth of coolant i just put in but i may have to. this is the wifes car so i don't want something catastrophic to happen when she's riding with the kids but i need to keep trying the DIY methods due to income issues.

[davebigs]

I say take out the thermostat and run the car, if nothing changes then you iliminate that possibility. As far as head gasket goes, i would look at the tail pipe to see if you are getting a lot of steam there, you could also have someone follow you and see what your exhaust looks like..

[shorod]

Since the temp gauge drops when moving down the road, I don't think the thermostat is the issue. Likewise I think you would likely have boil over issues from a headgasket failure when running down the road. If a headgasket were leaking into the combustion chamber you would likely be able to smell it in the exhaust and get bubbles/boil over in the reservoir, like davebigs mentioned. If it was leaking into the oiling system, your oil on the dipstick would look like chocolate milk. If it was leaking to the outside world, you'd get steam with a sweet smell. Any of these would lead to a drop in the level in the reservoir, assuming the system is full enough to continue to pull from the reservoir. That gets back to the question of the level in the reservoir changing when cold versus hot. If the level is not changing, then there is still a chance you have air in the system and it is not able to pull from the reservoir. Does your Cavalier have the pressure cap on the reservoir, or is there a pressure cap on the cooling system and a separate cap on the reservoir?

-Rod

[moliva1568]

it has the pressure cap on the resevoir. i noticed today on my way to work it still did it but not as much. i ran it earlier without the cap to try and release any air. i didn't have as much traffic today so it's not a real comparison. should i run it again without the cap? if so, how long is sufficient.
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[Mavrick14]

Running the car without a t-stat is a dumb idea, do not do it.

If the engine stays cool while moving but heats up at a stand still then your problem lies within either the electric fans or the rad. If your fans are kicking in when the temp gauge is between 1/2 and 3/4 then they check OK. Your problem is either debris in the rad/condensor or a partially plugged rad or fan efficiency, but you said they are blowing hard so they're OK.

As for checking for a bad head gasket.. 1) watch for white smoke out of the tail pipe (may smell sweet) 2) borrow a cooling system pressure testor, and see how long your cooling system holds pressure with the engine off 3) With the engine running and the rad cap off, watch for bubbles or exhaust gas.

Bleeding the cooling system - You have to run the car with the heater on until the thermostat is open (temp gauge at or over 1/2), and continue topping up the coolant reservoir for 10-20 minutes. If you've been driving it for a few days (with the heater on*), and your hoses are pressurized, then I wouldn't worry about air pockets. Your gauge comes down when moving, and goes up when still.. i dont think air is your problem.

Borrow yourself an infrared thermometer and point it at the thermostat housing to see what the actual temperature is, your gauge may be out to lunch. Also check the temp difference between the upper and lower rad hose, there should be atleast a 20-30degrees F difference.

[moliva1568]

my heater doesn't blow because the blower motor is out. i believe at the 3rd speed it lets out a little so i'll try that. the infrared thermometer i would find where?
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[Mavrick14]

Dont need a blower, just have the heat ON to ensure that coolant is flowing through your heater core. In a cav, it probably doesnt matter.. some vehicles have a valve, that is why you want the heat on.

The thermometer.. snapon, matco, any big tool brands should carry one.

[MagicRat]

Originally Posted by Mavrick14

The thermometer.. snapon, matco, any big tool brands should carry one.

Stores that specialize in barbeque and grille sales and service carry these too, sometimes pretty cheap.

[Blt2Lst]

Originally Posted by moliva1568

i changed the thermostat and it doesn't seem to have helped.

When you changed the T-stat, did you also flush the cooling system out?
While the system is drained, you can look inside the radiator to see if there is any corrosion build up around the cooling tubes, if so, it might be time for a new radiator.
If there is no cap on the radiator, you can remove the upper hose and look inside.

[moliva1568]

no i didn't flush it. what's involved with that?
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[shawcross]

clean the outter side of the radiator just so the air can move freely threw the rad as the cooling fan does it job

[moliva1568]

I know this is an old post i created but here's an update. The overheating issue never really got resolved. I changed the waterpump and sprayed down the radiator hoping to clear any possible debris. The system was bled but the coolant was not flushed. Now the weather is much colder and the car runs cold. However even, with the gauge near C, once I get into traffic or stop and go situation, the neeedle eventually makes it way toward the H. There still and never was any signs of coolant leak. Any ideas now? Maybe I got a bum thermostat?

[Mavrick14]

You can check your t-stat with an infrared thermometer, and measure the temperatures before and after the stat as the car warms up. It should be warm on the rad side, and hot on the engine side until the stat opens up and then the temps should be the same within a couple degrees.

Pretty rare to get a faulty t-stat, but you said the car runs cold now, and eventually overheats in traffic - that sounds like a stat stuck open.