98 cavi probs

ok heres the deal i am stumped here, we have a 2.2 motor( not ecotech) and when we are driving the motor is fine as soon as we turn on the heat it pegs the temp and and almost wants to overheat (this happens as soon as we feel heat) and when we shut the heat off the temp returns to normal.

We can drive for hours with no heat car is fine, then soon as we turn on the heat and it is felt inside of car it pegs it hot.

ANY HELP please don"t wanna dump a boat load of money to just realize it was a 10 dollar part, AND PLEASE no backyard mechanics i have enough of them at my disposal Including me.

So someone help who can really really know please,this is my fiance's car and don't need her freezing going to take lil one to school and her to work, Thanks in advance

What heat mode are you turning on. Vent, floor, defrost, or doesn't matter? Does the blower mode speed make a difference? Have you confirmed the actual engine temp with a scan tool when this happens? does it do it with the temp in the cold position as well? How long does it take to for the needle to peg after you turn on the heat?

What heat mode are you turning on. Vent, floor, defrost, or doesn't matter? Does the blower mode speed make a difference? Have you confirmed the actual engine temp with a scan tool when this happens? does it do it with the temp in the cold position as well? How long does it take to for the needle to peg after you turn on the heat?

1. it pegs it no matter what setting its on i.e. fan speed 1,2,3
heat,defrost,floor or whatever

2. do not own that tool but when its overflowing out of overflow i would say its too hot LOL

3.if i DONT have the heat on it will drive just fine hours upon hours no probs

4. it will will only take 45 seconds to a minute to overheat


so far this is what i am finding out...........clogged rad maybe or the sensor above the thermostat bad or just a bad thermostat

I wonder if your on the right track with a clogged radiator but externally between the A/C condensor and the radiator. If the a/c is on (assuming there is a switch that allows you to turn on the a/c with any zone setting) with the heat on the a/c condensor will supply additional heat to the radiator. If there isn't good air flow through the radiator than it can't cope with the additional heat. With the heat off (and the a/c off) there is enough air flow through the radiator to handle just the heat transfer of the engine.

What do you think of that theory? :)

That's an odd problem. Was it OK over the summer? Does it overheat with the A/C or the vent on? I would think that when it's cold enough to turn the heat on, the heater core would be dissipating enough heat to make up for any heat from the condenser.

How much coolant came out of the reservoir? It may have been overfilled and just got hot enough to push a bit extra out. You could also have a bad pressure cap and bad coolant that is letting the coolant boil. If the coolant is dirty or of the freeze protection isn't low enough, flush it. Also check the pressure cap, I believe it should hold 16 PSI, it says on the top if it isn't worn off.

Lacking a scan tool, does the heat from the vent get extremely hot when the gauge pegs? Get a cooking thermometer and stick it in the vent, watch it as the gauge moves up. I have found that the vent temp (assuming the heater core isn't plugged) is usually about 30-40 degrees cooler than the ECT. If the vent temp stays in the 150 degree range (after the engine has reached operating temperature) when the gauge pegs, then I would say there is most likely a ground issue with the blower motor, interfering with either the gauge or the sensor. You could try giving it a redundant ground... Check whether the resistor/switch is on the power or ground side of the motor, you'll have to put the ground after the switch if it's on the ground side. Or as a quick test you could run the ground directly to the motor, but that will make it stay on high if the control is on the ground side.

I wonder if your on the right track with a clogged radiator but externally between the A/C condensor and the radiator. If the a/c is on (assuming there is a switch that allows you to turn on the a/c with any zone setting) with the heat on the a/c condensor will supply additional heat to the radiator. If there isn't good air flow through the radiator than it can't cope with the additional heat. With the heat off (and the a/c off) there is enough air flow through the radiator to handle just the heat transfer of the engine.

What do you think of that theory? :)

not big on theory's but thanks

That's an odd problem. Was it OK over the summer? Does it overheat with the A/C or the vent on? I would think that when it's cold enough to turn the heat on, the heater core would be dissipating enough heat to make up for any heat from the condenser.

ME:No i didn't over heat at all with the air on, it was fine over the summer had a few gurgling sounds but attested that to an air bubble and took care of it, no more bubbling (gurgling sound)


How much coolant came out of the reservoir? It may have been overfilled and just got hot enough to push a bit extra out. You could also have a bad pressure cap and bad coolant that is letting the coolant boil. If the coolant is dirty or of the freeze protection isn't low enough, flush it. Also check the pressure cap, I believe it should hold 16 PSI, it says on the top if it isn't worn off.

ME:It over flowed enough to have to add almost a half gallon of anti-freeze when it happened, and had the cap tested at shop was at 15 pounds,and all this trouble started AFTER i had the rad flushed dammiit anyways




Lacking a scan tool, does the heat from the vent get extremely hot when the gauge pegs?

ME: it only lets you first feel the heat and then it pegs it, would not be able to get a reading before it boils over, and it only does it when the heat is on, we drove for 130 miles with no heat not a problem as soon as we turned heat on like in 45 seconds to a minute she wanted to over heat............EDIT WE HAVE CHANGED THE THERMOSTAT AND THE SENSOR RIGHT BY IT STILL NO LUCK 10/13/09 9:00 PM


Get a cooking thermometer and stick it in the vent, watch it as the gauge moves up. I have found that the vent temp (assuming the heater core isn't plugged) is usually about 30-40 degrees cooler than the ECT. If the vent temp stays in the 150 degree range (after the engine has reached operating temperature) when the gauge pegs, then I would say there is most likely a ground issue with the blower motor, interfering with either the gauge or the sensor. You could try giving it a redundant ground... Check whether the resistor/switch is on the power or ground side of the motor, you'll have to put the ground after the switch if it's on the ground side. Or as a quick test you could run the ground directly to the motor, but that will make it stay on high if the control is on the ground side.



I answered in color see above

all this trouble started AFTER i had the rad flushed

This is where I would change my thermostat.

this is where i would change my thermostat.
edit we have changed the thermostat and the sensor right by it still no luck 10/13/09 9:00 pm

If it happened right after the radiator was flushed and a thermostat didn't fix it, I wonder if there is some air in the system. Not really sure why it would overheat only with the heater on, unless there's a heater control valve in a heater hose, but I'm pretty sure no Cavaliers have that. Gotta be something though, I'd try bleeding any air out, might get lucky and that'll fix it. It's nearly free to try, worth a shot :)

If it happened right after the radiator was flushed and a thermostat didn't fix it, I wonder if there is some air in the system. Not really sure why it would overheat only with the heater on, unless there's a heater control valve in a heater hose, but I'm pretty sure no Cavaliers have that. Gotta be something though, I'd try bleeding any air out, might get lucky and that'll fix it. It's nearly free to try, worth a shot :)


That was my next thought,but as youstated their is no heat control valve.:banghead:

That was my next thought,but as youstated their is no heat control valve.:banghead:


I believe next step is radiator for it had 3 cool almost cold spots on it after driving for a 35 mile round trip, so rad i think is clogged in some spots ....it does have after all 145797 miles on the original radiator anyways so will update ya in a few days

Sounds like you probably have a clogged cooling system and/or air in the system. What I like to do before replacing anything is, install a Prestone flush T in the heater inlet hose. Flush all the coolant out with a garden hose. Then put in a bottle or two of radiator/coolant flush and refill with water. Run engine till hot. Then if you have access to a hot water outlet, like your washing machine hot water spicket, hook the hose to that (I like to turn the water heater on max several hours before so not to run out of really hot water to fast) and then flush it again. If you can't hook it to hot water just let the engine cool for awhiel and then flush out all the cleaner with cool water. This will normally clean out a clogged coolant system unless its really bad, but even so it still needs to be flushed good like this.

I believe next step is radiator for it had 3 cool almost cold spots on it after driving for a 35 mile round trip, so rad i think is clogged in some spots ....it does have after all 145797 miles on the original radiator anyways so will update ya in a few days

Try one more thing before you replace the radiator. I had an '01 2200 in the shop today (assuming here that it's the same design as yours). It's possible that the passage got plugged up with sludge and the air is unable to exit out to the reservoir. Pull the hose off and make sure that both the hose and the fitting on the pipe are clear.

If that doesn't fix it, then I guess replace the radiator. I honestly don't think that's causing it, but it has to be something and I can't tell you what else it could be. See if the cold spots line up with the openings in the grille. A plugged radiator shouldn't cause your problem anyway, having the heat on removes more heat from the system. But like I said, I can't say what the problem is, so I probably shouldn't say what it isn't.

I forgot to mention while flushing the system also replace the thermostat and pressure cap.