02 Chevy Cavalier Temp Gauge Goes Up When Heat is Turned On

Hi mmchny,

It sounds like there's a blockage in the heater/defroster or maybe the radiator itself. Was the radiator and core flushed? The water pumps on these engines are internal. It may be your problem.

57,000 miles is not high mileage for these engines. I've owned 4.

cc732

Thank you for your input. No, the radiator and core have not been flushed. The heat works great. I'll try having them flushed and see what happens.

Thank you for your answer. I'll have them flushed and see what happens.

I think it will fix it. As a slight aside, since you are the proud owner of a Cavalier, you may want to consider purchasing a Haynes manual and doing some of this yourself. It will save you a lot of money. Just my opinion from the Cavalier threads on here............................................but it seems like once you've spent $100, you have entered the land of diminishing returns.

If he makes the purchase, clear instructions are on the back of the package with both words and pictures. Heater inlet hose.

Much clearer. I actually put one of these on an old Pontiac Sunbird I drove. Don't recall it helped anything. Didn't hurt anything either.

They work okay for a quick flush. For a real flush, it's imortant to disconnect both heater hoses and flush out the heater core in both directions. I could get into explaining how regular white vinegar makes a good flushing agent when run through the system for 15-20 minutes, but I'm only going to spend so much time on a Cavalier thread.

Has anybody ever sat down and tried to calculate how many things can actually go wrong with a Caviler, vs how many we've already seen here?

I had always thought that the Chrysler K car series was the worst ever made, but I was wrong. At least those were designed for a quick death.

It's products like these that give engineers a bad reputation.

I've actually had very good luck with this car. No major problems. I did see the extensive posts on Cavaliers. I would like to have the Haynes Manual, it would be a great help. The thing I don't like about the car is that the top of the radiator is not accessible. I have to fill it via the overflow tank. I will ask my mechanic to do a thorough flush in both directions.

Some of us get lucky. I've got a 99 Dodge Caravan that also seemingly has a bad reputation. It just turned over 252,000. I'd better go find some wood to knock on.

Yeah, the Haynes manuals tend to be better than most of the others. Especially if you're not accustomed to doing your own work. Nice, easy to understand, step by step instructions........................with pictures.

I have to think the water is going out the tail pipe. Maybe have him check the spark plugs for rust.

I have no clue why turning the heater on would cause overheating. AC yes, heat, no.

Is the fan working?

57K miles is low.

Good luck.

Well I'm no expert, but it sounds like the heater is leaking....It was fine until you ran the heater... I'd fill it up, turn the heater on, and watch for leaks....

There's water running through the heater core all the time. Temperature control is done with vacuum operated flapper doors on the air vent system.

Well it's got a leak somewhere, just fill it up, let it run, and wait...It's gotta be coming out somewhere, if only in steam...If it was overheating with a bad core it would be filling up the overflow, unless that's cracked...

If this car has old-style ignition with a vacuum advance unit on the distributor, and if the vacuum connection to the heater control is leaky (a not infrequent occurrence in older cars) turning the heater on may reduce manifold vacuum enough to change the ignition timing (retard it) and cause the engine to run hot. The quick and dirty fix for those ornery little vacuum hoses is just to cut an inch or so off the end.

Although getting to the end of the hose at the actuator or at the heater control is probably a bear, because both are likely behind the dash, the problem usually occurs first and worst in the engine compartment. The elevated temperatures, vibration, and fumes in that location are all hard on rubber goods.

I will have a guess, sight unseen.

A leak is the obvious diagnosis. You don't see a leak though.

The heater core might be leaking and pouring in under the floor mats. Have you lifted them to check for the presence of coolant?

It might also be leaking into the A/C condensate pan. Is the condensate drain pipe dripping or pouring out something other than clean water,?

You figure a coolant leak, anywhere, would show up on a pressure test....

Maybe it's not leaking at all but under filled with a huge air pocket in the cooling system that gets disturbed when the heater is really convecting and causes a gulp with a drop in level....or not.

The water pump may not be leaking but may have a an impeller that doesn't "impel".

Anyhoo...per my opening caveat. These guesses are made sight unseen.

As suggested before, keep looking.

Did you have the temperature sensor checked? A bad temp. sensor can cause false indication, like reading hot, when it's not. Did you check your interior front floor carpets to see if their wet? Wet carpet(s) will indicate a leaking heater core. And as far as lost coolant, you may have a 'Freeze Plug' or also known as a soft plug leaking from either the engine block or head(s). Depending where you park the car, you might also put something like cardboard under the car after you warm the engine up and look for leaks or stains on it. If you try this method, do not pull the cardboard out, just move the car straight back and then inspect the card board. If you see any stains, you can estimate what and where leaks are. And like what Lyn said, check the spark plugs rust or moisture. The cooling system is a close system and the coolant just doesn't evaporate. Again, like what Lyn said, turning the heater on will cool the engine, the AC will cause it over heat.

Check for a leaking water pump. It is tucked in behind the block, driven by the cam belt. The girl friends went and I changed just about everything before I found the problem. Quite a job to change.

Vic

i've seen people, including me, who have installed the thermostat upside down. pull it back out. the pellet should face the engine.

Check underneath the passenger side floormat for water. You may have a leak in the heater core this will drip into the cabin area and not be visible from under the hood or below the car.

Let us know what happens after the flush. I'm guessing that the heater core is clogged up to the point that it's slowing down circulation, which is causing overheating. Water is probably escaping as steam from the vent cap.

Don't think so. Engine cooling water doesn't flow through the heater core.

It does on my stuff. Are they using electric heaters now?

What flows through the core, oil?

http://www.autopartswarehouse.com/shop_parts/heater_core/chevrolet/cavalier.html

I knew I should have explained. You can block the heater core off and not affect engine cooling very much. The water that flows through the heater is cooled and it does help cool the engine, a little. Earlier Ford products had a valve on the inlet side of the heater core that you could use to shut off water flow to the heater, before AC and fancy air venting came along.

I'm sticking to my guns on this one. It only gets hot when he turns on the heat. We'll see what happens after he has the cooling system and core flushed out. Flushing the core separately. I'm guessing that not only the core, but the radiator and entire system is crudded up. When he turns on the heater, it's slowing down the circulation within the entire system to the point that it's getting too hot and boiling off. One of us is going to be eating crow, I can only hope it's you.

All I can do is guess, since the story is a little odd. If the thermostat was stuck open, I'm surprised that he had heat at all, much less going into an overheating condition.

"One of us is going to be eating crow, I can only hope it's you"

Do you want it grilled, or boiled?

If one looks at surface area and air flow through the heater core, it really doesn't provide much cooling for the engine.

No, it doesn't provide cooling for the engine, but when he turns on the heater it increases the flow path of the coolant. If everything is gunky, it could slow down the flow enough to cause overheating. Not to mention, if I'm right, he's also making his water pump work harder than it needs to, by having to push coolant through a partially blocked radiator and heater core.

I like mine grilled...................you?

Oven roasted, with a side of deep fried beaks and feet.

I had a really crappy day at work. So, I'm takin' it out on you.

You said, "when he turns on the heater it increases the flow path of the coolant"

I say the coolant flows all the time, regardless of the state of the fan.

Think about it. Why would they put an electrically, or vacuum, operated $ control valve on a liquid line under pressure when they can just divert the vent air to control cabin heat. On A Caviler, yet? The water runs all the time.

Yeah, it doesn't make sense. If anything, you would think that it would get slightly cooler when he turns on the heat, but I don't know what kind of weird stuff they have on these new cars. The heater core is inside, behind the dash, so there just might be something that controls coolant flow to it. Which would make sense. There is absolutely no other logical reason that I can think of that would cause the temperature to rise when the heater is turned on.

Go ahead and take it out on me.....................gloating will be so much more fun when we find out I'm right.

Has this car got an automatic transmission? This is going to sound really weird but check your transmission fluid. My 01 cavalier had a similar problem. No one could figure out where the fluid was going. Turns out the coolant was mixing with the transmission fluid. My mechanic said he has only seen this happen once or twice in all his years usually only after an accident. My wife did have a fender bender about 6 months before we started having problems. We Only found it because the transmission was suddenly not shifting like it usually would. It was due for fluid replacement anyway so I took it in to get it serviced and they discovered coolant mixed with the transmission fluid.

The heater is the clue here. But yeh, coolant can leak through into the tranny if the heat exchanger in the radiator is wallaby ted. You'd expect to find tranny fluid soup in the radiator as well.

A poltergeist perhaps.

My two guesses are first: the air conditioning compressor is running when the heater is turned on, but both radiator cooling fans aren't running so the engine gets hot. If this is the case, you may have a stuck relay for the clutch on the compressor and/or a bad radiator cooling fan.

Second guess is the waterpump is leaking, but you won't notice it when the engine is running, and unless they really go bad, they don't visibly leak when the engine is off and while it's off, the engine will pass a pressure test. If all you're running is pure water, you can kiss your waterpump seal goodbye.

I doubt the heater core is leaking because it would leak whether the heater is on or not. The valve that supplies water to it only shuts off the supply side, and you would still have pressure in it from the return side.

An old trick when you car is overheating and you need to drive it a little farther is to turn the heat on full blast. The heater core will help cool the motor down provided there is still fluid in the radiator. Usefull if you're towing a load up a long incline and your engine is getting hot.

Was the rad cap also pressure tested? A slow leak at any of the upper hoses may have missed notice as there would be only air escaping. Just try inspecting the clamp connections carefully with an educated eye. Heaters will have pressurized water in them when ever there is any pressure in the cooling system. If there is a heater shut off valve, it will only be in one of the hoses. The other hose will still provide pressure to the heater system. I believe there is a coolant leak that is slow, and just not been found yet.

My recommendation is:Jack it up as high as possible.A garage lift will do fine.

Carefully inspect the bottom side of the car,engine compartment,all hoses,fittings,connections,etc.

Then,while you have it about 6 feet high, back a Honda Accord under it and drive the Honda home.Problem solved.

I had a Cavalier, and the best way I found to solve the multitudinous display of engineering ineptitude,inadequacies and lack of common sense problems was to do as instructed above.I have never regretted it.

So much was I alienated by that car that I will NEVER buy another Government Motors Vehicle of any type.I am sure there are a few good ones out there, but like UFO's I have never actually seen one.

The above statements of course, are my personal opinion, and do not reflect he opinion of anyone else,either directly or indirectly, obtusely,or bluntly,implied or explicit.I make no claim that my opinion is better or worse than any other opinion, or that by expressing my opinion that I am implying that I am better than anyone else, or that anyone else is of lesser intelligence or judgment than me.

Acceptance of this opinion implies agreement with the foregoing terms and conditions, and is void where prohibited by law, rule,regulation, agreement, accord,convention, or covenant, and holds the originator of this opinion blameless for all consequences which may arise from use, abuse, or misuse of said opinion in any and all circumstances.This opinion may be copied freely without charge as long as the exclusions above are included in every copy,within or outside of this time continuum (present),future or past,or the infinite possibilities that may or may not exist between these continuums, and nothing may be construed to claim otherwise.These conditions are universal, and apply to every civilization, sentient or otherwise that may exist now or in the future, or may have existed in the past.

You have my sympathy.

"A town that is too small for a lawyer, is large enough for two lawyers!"

Thank you all for your input and suggestions. Will be taking it this week to get radiator flushed. When I asked about flushing the heater core my mechanic said that he usually blows it out with air. He told me a way to check to see if heater core is blocked is to feel both hoses and if one is lukewarm, then there is a blockage. I also have to check to see if the cooling fan is operational. I did notice that when the defrost is turned on that the a/c indicator light comes on and and it sounds like the compressors is on. This happens only when the switch is on defrost only. When I put on to the combination defrost/heat the light shuts off and I do not hear the compressor. Since there is no access to the radiator cap I have been checking the coolant level via the overflow tank. There are the two indicating lines on the tank which say full cold and full hot. When I take the cap off I can see some coolant but it is not up to either of the lines. I was just told by my son that there should not be any coolant in the overflow tank because it should be full only if the pressure rises so the coolant has somewhere to go instead of boiling over. That being said, how do I determine whether the coolant is low if I cannot see the radiator?

Have your mechanic disconnect both hoses to the heater core and blow it out with water and one of these on the end of a hose. Air isn't going to do it. Also, your son is wrong. You will see an indicator mark on your overflow tank for where the level should be. As the engine cools, it draws water back into the cooling system from the overflow tank. Let us know how it goes.

Thanks. I'll ask him to do that. Should he blow out both hoses or just one? So when the engine is cold I should be filling the overflow tank up to the full cold level and then keep an eye on the level. I'll let you know what happens.

Have him disconnect the hoses where they attach out by the engine and run the water through the hoses in both directions, in one and out the other. I didn't think it would make much difference either until I tried it. the heater core collects a lot of gunk.

Yes on the overflow tank.

Keep us posted. I want lyn to be wrong.

Do not allow the hose that is not connected to the garden hose to point anywhere near you. The rusty crap that may come out of there is going to look like rusty mud. It is messy.

Try to determine the direction that coolant was flowing into the heater core when it was working. Then flush in the other direction.

First fill the radiator to full, then fill the plastic reservoir to the full cold mark. then start and allow to warm up. shut off, and allow to cool. Recheck the reservoir level again. If it is now empty, refill the radiator and the reservoir again and repeat the start-stop-cool cycle again. Good luck.

You can fill the radiator through the coolant bottle by cyclically warming up the engine and allowing it to cool.

Make sure that the coolant expansion bottle is filled prior to warming up the engine.

You will know when the cooling system is as full as you can get it when the coolant stops going below the "cool" line after being sucked back into the radiator during the cooling cycle.

The coolant expansion bottle should never be empty least the radiator will be gulping air instead of coolant during cool down.

This is just for future reference

Get your cooling system properly and competantly serviced.

This post has many replies and I haven;t read all of them, but have you changed the thermostat? Another thing to check. Get a mirror and look at the neck of the water pump. There is a hole in the neck of the water pump housing, this may be well hidden by the pulley that the drive belt rides on. If you see any staining at all around that hole that is where the leak is. Or let me put it this way, it is leaking there if it is stained. It may only be leaking while the engine is hot and running so you will not see many liquid when the motor is stopped. If you remove the belt and spin the water pump with your hand you may notice some roughness or noise or looseness. The increasing lack of concentricity, due to a worn water pump bearing causes the water pump seal to lose sealing ability because of the alignment mismatch. Good Luck!

My radiator cooling fan has not been working. I turned on the A/C compressor button to run the A/C and after that the cooling fan finally kicked on. I shut it all off and then without turning on the blower fan switch or the heat/A/C switch I just pushed the A/C button and my drivers side rear window went down. I've had problems in the past with the A/C switch not working properly, had it replaced last year along with a new compressor and this year the A/C did not work. Having my mechanic look at it today but this new wrinkle is really frustrating. It's always something.

That's the 4x40 airconditioning system in action.

4 windows down at 40MPH.

Went to my mechanic yesterday. When I drove it in it was running hot and boiling over. Coolant leaked out onto floor. He didn't have much time so he first tried to determine where coolant was leaking from. We checked out the water pump and no signs of leakage. He tried pressure testing and couldn't get any pressure. He then disconnected one of the hoses from the reservoir, attached a funnel and added coolant into system that way. Coolant started leaking out. Put up on lift and he got up on ladder and added more coolant and we found it was leaking out of the seam in the chassis under where the overflow reservoir tank sits. There is a short overflow hose off the tank through which coolant flows out when boiling over. He held the hose up while pouring in more fluid and it did not leak out. We were trying to determine whether the reservoir tank could be cracked and that is where coolant is leaking out. Didn't have enough time to remove it and check it for cracks. It is most likely a dealer item only so I don't want to replace it if not necessary. He did flush radiator because we didn't have time. He didn't think it was clogged because the vehicle has only 63,000 on it but I still think a flush couldn't hurt. We filled the system back up and I drove a few minutes up the street and started to hear a rattling sound. Drove right back and it was real hot and smoking. He took off reservoir cap to relieve some pressure. Had him come for a ride with me and of course it did not make the noises it was making when I just drove it. I have to bring back next week and leave for the day so he can remove the overflow tank to check it out. Strangely on the way home it is now running ever hotter that before. 3/4 of the way to 260. Drove home. Let it cool off for about an hour and checked reservoir. Very little coolant so it must have leaked out again. I think I'll also have him check the new thermostat just to see if it might be faulty. Don't really want to drive it too much because it is running so hot. Don't want to cause any damage to engine, plus coolant is too expensive to keep adding when it is just going to leak out anyway. Will keep you posted on the next visit to mechanic.

Did your mechanic pressure test the radiator cap? If not ask them to do so, maybe just a cheap fix. It wouldn't be the first time to hear the heart aches a bad cap will cause. I saved a friend $2,500, that the dealer wanted for a head job, (on the engine), just by replacing a $13.00 radiator cap!! And, if does turn out to be a cracked reservoir, I would check with a local wrecking yard for a replacement or an after market one, which I'm sure would be cheaper than the dealer.

Hi All,

Sorry to take so long for an update. My mechanic blew out the heater core with air. Said it was all clogged with jelly. It ran okay when he took me for a ride right after. The car sat for a couple of weeks after and then the first time we took it out we drove for about 5 minutes and made a stop and left the engine running and the temp gauge shot up again. It is okay on the highway but when you get into traffic or stop and go the temp gauge goes up. It is also leaking coolant out of the overflow hose. My mechanic replaced the thermostat and temperature sensor. Cannot replace radiator cap because there is none. I am taking it back to my mechanic and asking him to flush heater core with water this time. I am wondering if not driving the car on a daily basis is causing the problem. Before this overheating problem started the car was not driven very much over the course of several months. My mechanic says the the Dex-Cool antifreeze tends to turn to jelly. Is there any other type of antifreeze I can use or do I have to use the Dex-Cool only?

Thanks for getting back.

I think your cooling system is going to require multiple flushes. Once it is cleaned out, letting it sit shouldn't be a problem. Although, if it's for long periods of time, you should at least start it once a month. You also run the risk of encountering fuel system problems, due to the mandated ethanol.

Use the antifreeze that it calls for in your manual. Don't ever, ever, mix different colors or types of antifreeze..................nothing but problems. If Dex Cool turns to jelly, I would find a suitable replacement.

Thank you. One question. When you do a radiator flush does it run through the heater core as well? We plan to drive the car more often once we get the problem fixed, at least once a week. We are wary of driving it with the overheating problem because we know it is low on antifreeze and don't want to cause any engine damage. I am going to insist that my mechanic flush the heater core with water this time. I hope he is willing to do that. Should we have the radiator flushed again as well?

Post #50.

I think you might want to look for another mechanic. He didn't flush the heater core with water?!!!

Try to flush the entire system , not lust separate components. Flushing will work best if the thermostat is removed first. By squeezing the radiator hoses during the fushing process, you can force water to flow through the heater core. Just be sure that any heater control valve in the heater hoses are wide open.

Vehicles that heat up in traffic, or low speed operation, are usually not transferring sufficient heat through the radiator to the air stream. It could be an electric fan not operating, a restricted radiator air inlet, a fan clutch not locking up on demand, or even a fan not pulling air through the radiator.

How is your fan driven, belt drive, or electric? Most electric fans are also turned on whenever the air conditioning compressor is turned on. Try driving with the A/C on and see if the overheating continues if yours is an electric fan. Good luck.

Did you ever find a solution to this problem my car is doing the same exact thing??? Please help.....

First off, welcome to the site. The original poster went through a long slow period of diagnosing his problem. Try not to throw parts at the car because someone else needed that part. That will just make the parts store richer.

Either follow the diagnostic route in the above posts, or post your exact problems, along what you have done to resolve the problem. Good luck.

Hi,

Yes we solved the problem by having our mechanic blow out the radiator with air about 3 times. The reason for our problem was the the car sat for almost a year without being driven on a regular basis. The Dexcool antifreeze turned to jelly and caused a blockage in the radiator. It took 3 times of him blowing out the radiator with air to fix the problem. Every time he said he saw jelly (antifreeze) coming out. Once we started driving it on a regular basis we have never had another problem with it. Read all the posts as there is a lot of good advice. Anytime you let a car sit for too long, problems arise. Good luck.