thermostat

I have a 1995 Chevy Corsica, 6 cyl. with almost 60000 miles on it. I noticed that my temperature gauge was slowly going past the haflway mark when the ac is running. I turned the heater on and the guage did go back down. This only happens when I first run the car. Once I turn the heat on and the guage goes down I can turn the heat off and turn the ac on and the guage runs perfect. Today the guage went all the way over to hot and I turned the heater on but that did nothing. I finally had to turn the car off and let it sit. I turned it back on again but the guage still was all the way over to hot. After a couple more tries of turning the car on the guage finally went back to a normal reading and I turned the ac back on and it was fine. I have had the thermostat replaced. I'm not quite sure what would cause this to happen. My mechanic has tested the car and of course the guage does not go to hot when it checks it. Any suggestions?

Thank you

 

I would have the system flushed to get any debris or air out of the system. If that does not help, then it might be a failing water pump or head gasket leak. Does your oil look normal?

 

It's possible you have a bad sender. The critical question would be, was the coolant ACTUALLY that hot or was it indication. If it is actually getting hot you want to be real careful about running it hot for any length of time as it is really easy to blow a head gasket that way. Might be worth the few bucks to simply replace the sender. Could also be a bad wire in the indicating system since it works on resistance and if you were to disconnect the sender and short the terminals the indicator would go to the top (hot). Same thing would happen if the wire was shorted to ground anywhere in the circuit.

And as a side note, turning on the heater and getting the temp down may have been coincidental as your heater core always has coolant running through it, i.e. it is always hot.

 

Greetings, OKC.

 

Thanks for all of the help. I did have the system flushed in Jan. of this year.
I had the oil changed yesterday and they always check for leaks. They did do a pressure test on the system and they said everything checked out. I'm hoping it is a bad sender. Water pump sounds expensive. Is there any kind of test to check the water pump? I want to take the car in tomorrow but if the temp guage doesn't go all of the way to hot they will just say they found nothing wrong which is understandable. Thanks again.

 

"Greetings, OKC"

Hello there Mr. John. I find myself on these forums most of the day. I really need to find a job.

 

Should have re-upped.

Not really any way to test a water pump. Most common failures involve external leakage or bearing failure which can be diagnosed by relieving belt tension and checking to see if the shaft has any wobble to it or noise when turning.
The intermittent nature would tend to make me suspect either indication or thermostat, but you've already replaced that and if the pressure test was done properly that should eliminate the head gasket. Also something we failed to address was your cooling fan(s). Were they running properly when you had the hot indication?

 

When my car was running hot I did not get out and open the hood to see if the fan was running. Dumb me never thought about doing that. The car is at the gas station right now and they are going to try and check everthing they can think of to resolve the problem. I would love to lean toward a bad guage..........another question I have is that when the guage runs all of the way over to hot and if I let it just run would I not risk having steam come out of the engine? You can see I don't know alot about cars. I do check my fluids and my tire pressure and change my air filter but that is about as mechanical as I get. If they don't come up with anything today the next time this happens should I just let it keep running and open the hood to see if the fan is running?
Thanks for all of the help.

 

OK, I just got my car back and they said that the coolant cap valve failed the test so they replaced my radiator cap. They checked the fan and said it was fine. He also said that the guage did go over the halfway mark and and that is when they tested the cap. I am hoping that replacing the cap has solved the problem. Thanks again for all of the help.

 

We both should have had radiator cap on our list of possibles [towguy and OKC will now slap each other].

To answer your question, any time the gauge goes to "hot" you need to immediately investigate. Running a modern engine hot for any length of time is a serious risk of blown head gasket and warped head(s) - i.e. steam from the engine. This is fairly widely misunderstood with the motoring public today. I can't count the number of vehicles I've towed where the temp was ignored [leaking radiator, bad hose, thermostat, radiator cap, water pump, whatever] and a $100 repair bill quickly became a $1000 repair bill. Not like the old days where you overheated and pulled off the side of the road, waited a half hour, poured water back in the radiator from a nearby creek, and went on your merry way.

 

OK, here we go again. New radiator cap and things were fine until today. I only ran the car for about 10 minutes and it is fairly hot and humid outside but again the temperature gauge past the three quarter mark and I pulled into a parking lot and stopped the engine. Turned it back on 10 minutes later and the guage went right back down. I know my mechanic can't fix anything until he sees it happening but the first time he saw it the thermostat was replaced. I asked him if maybe the guage was getting false information from a computer in the car and he said the guage problem is not realted to a computer in the car. Any other suggestions. I just had the battery replaced and the alternator because the car broke down and just died. 400 dollars later and now it's back to the guage again.

 

Do a compression test on the cylinders. The can determine if a gasket is leaking most of the time.

Have someone with a scan tool hook up to your diagnostic port and see what the actual temp reading is, this will rule out if the gauge is bad or not.

 

Thanks so much. I will be talking to my mechanic tomorrow and I will ask him to do this. Thank you so very much.

 

And you're NOT having to add any coolant?????.............Hmmmmm.......Chevy little six's (3.1 3.4) are well known for intake manifold gasket problems and that's where I would have looked first........It's possible that a head gasket is an issue......but with either of these you'll be adding coolant......
If the car is running smoothly it's unlikely a compression test will show up a head gasket.........Using a block tester (sniffing the vapors in the coolant system for traces of exhaust)will be a more accurate telltale.........

 

could be a air pocket in your cooling system or a bad relay for your cooling fan.one fan should run all the time with your a/c on and the other engages when temp. reaches around 200 degrees.there are bleeder screws on the coolant lines usually 2 of them,and its hard to get the air out of the system after flushing the system

 

Corsica is back in the shop again. I even went for a ride with my mechanic for the same lenght of time I had the car running yesterday when the guage went past the 3/4 mark and would you believe the whole time he was in the car the guage was fine. He said to leave it with him overnight and he would try in in the morning. I think I have a little demon in my car just messing with me...........hmmmmmmmm. Maybe after I get my car tomorrow I will have some good news........maybe I should take an auto mechanic course.....
not likely............

 

IF - the car runs cooler down the highway, but then the gauge climbs when you are idling about town, in traffic, stop and go lights, then that means your radiator and thermostat and the general movement of coolant through the engine are actually quite good. But at low speeds, it is your radiator fan(s) that have to take over and cool. And if the temp ONLY climbs then, then this is your problem; fan related or the sending unit, telling it to come on, or maybe a fan relay, but I'd bet more on the sending unit. You probably have two sending units and if so, it is the one that has the most wires coming out of it and is probably in the thermostat housing. (The OTHER sending unit probably has one wire and only serves the gauge.)

And, if by chance it overheats going down the highway also, you need to check to make sure the fins are clear in both the radiator and the condensor for the a/c before anything else, as that is suych an easy check.

 

Thanks so much. How would they check if the fan is doing it's job because they said the second time I took it in that the fan was ok. And how do you check the sending unit. That is what I think it is. Since the system has been flushed, new thermostat and new raditor cap I think the sending you is giving the wrong information......but that is only my opinion......LOL........

 

http://www.autozone.com/az/cds/en_us/0900823d/80/14/76/d1/0900823d801476d1/repairInfoPages.htm#hd1-1-3

There is a test procedure for it.

The sensor is only $11.99 at Autozone.

 

That is incredible............thanks for the link.........you can bet I'm going to ask him about it tomorrow.

Many thanks

 

$400 invested with this fix and back to the gauge??
Those intermittent problems can drive your mechanic nuts and your wallet a lot lighter.
I would get a infrared heat gun to read the temperatures of the engine.
I don't think you can go wrong with the investment.
It will tell you if the engine is acually hot or if it is a sender or gauge problem.
Maybe your mechanic will loan you one and describe the best way to use it.

 

Just spoke with my mechanic. He drove the car himself again this morning and the guage did go up to the 3/4 mark then he send it came right back down. He drove it further and said the guage did fine. He is going to put it up on a lift today and disconnect the heater core and see if there is a blockage that is making the system run hot. He said the car is not overheating. They are going to run another "block" test to see if the fumes are getting into the system. He said they did that test once but they will do it again. Hopefully they can find and fix the problem today. Maybe there is a blockage........sounds expensive to me but anything now is going to sound expensive to me. I really don't think I need a new car.....can't afford it.
Only 60000 miles on it.

 

Let us know what they find. Unfortunately it sounds like the money meter is ticking like for a cab ride.

 

Got my Corsica back again today. My mechanic said that they have done almost every kind of test than can do. The only thing left is to check the connection to the heater core. He said they rerouted the heater core or disconnected it....not sure which.......he said I could have the car back if I needed it but to drop if off on Sunday night so the engine will be cold again on Monday and that is when he will check the heater core conntection. He said that when the guage goes to the 3/4 mark that it does come back down and that is the way it should be. The fans kick on and cool everything down.
I am going to run my car tomorrow........take a kind of test drive myself and see if it does it again. I will leave it tomorrow night and see if they can find anything at all. I did have a nice shock though...........they did not charge me for anything today because my mechanic said that will all of the problems I have been having that unless they actually have to fix something or order a part that it is ok. Thanks for everyone's help in this forum. I really appreciate it very much.

 

My car behaves like yours, actually. ONLY in traffic, and is fan kick-on time related.

I don't get their heater core theory though. Seems like you should be able to have car run cool off just radiator with heater core even all blocked up. At least in all my life so far I have never heard of anyone having to work on heater core related to diagnose overheating engines. What I HAVE heard though is that if your car does overheat, you can help cool it by turning on the BLOWER to help cool it down.

 

Got my Corsica back again today. They did a bypass of the heater core just for the sake of testing everything. I was told that the guage did go to the 3/4 mark again but the second fan kicked in and it was fine. Now I'm told that the temp of the engine or the coolant, can't remember which, was running a little high but nothing to be concerned about. He also told me that it was not over heating and the only time I should be concerned is if the guage went all of the way over to hot and steam started coming out. I DON'T NEED THAT. He also said that since I don't drive long distances that with the low speed driving that the engine doesn't cool down as fast and with long distance driving. Funny, I been driving short distances since I've been retired, 6 years now, and it's never done this. I'm a little concerned about the temp of the coolant running a little hot. So if the guage does go to 3/4 quarters and the second fan does kick in and cool it down it that ok?
Thanks again for everyone's help. Oh yes, he also said he thinks it is a bad sending unit and it would cost 150 to replace it so I had the choice of just running it like it is or spending the 150. I chose not to replace it.

 

Personally, I would find the problem.
Engines are not meant to overcapacite the cooling system

 

This thread has gotten kind of lengthy and can't recall all that has been said. But for the fun of it (or seriousness of it), have you tried to drive it just on the highway for like a short Sunday cruise, say for 7-10 miles one-way before any stopping, with no stop signs on the highway, to see what the gauge does? And then compare where the peak reading is to that of driving it in 25-30 mph city streets and making lots of stops and then see what readings you get on your gauge? Then report these back here.

 

I drove my Cosica today and the guage was fine. I was even in a minor car accident. Hit from behind. My car is fine. It it really hot and humid today and I thought if something was going to go wrong since the ac was running that today would be the day. I did talk to my mechanic this morning about the temp. of the engine and he said that it was about 200 degrees which he said is fine. I will be driving tomorrow so we will see what happens.

 

Keep an eye on this as sporadic temps that can't easily be explained can mean that you have air pocket that sporadically comes and goes/moves around, and can be caused by head gasket going, because exhaust AIR gets discharged into the cooling system where, when the thermostat is closed, the air can get trapped and then cause sudden fluctuations in temps when the stat opens, then closes. One of my old 4-bangers did this to where the gauge would climb near hot, then suddenly drop to cool, then gradually rise again, etc., etc., and one day she reallly went on me and the car locked up at a convenience store when the coolant poured into a cylinder after I shut off the engine and hydrolocked right then and there form a severly blown head gasket. My sisters V-6 did the same thing.

You don't want to be flirting around with overheating conditions in todays vehicles. 200 degrees (at this particular check), is good. Many stats are 195. Anti-freeze/water mix at 50/50 and pressure cap can raise boiling point to 265 degrees.

 

Thanks for all of the informatin. A couple other people have mentioned the head gasket. You can believe I will be watching the temp guage. I remember in 2002 that they found my coolant was low and that the anti freeze was in my crank case and oil system. They had to replace the manifold gasket. Another few hundred dollars. Hopefully the problem is resolved but if not........I don't even want to think about it. For being a 12 year old car with barley 60000 miles on it I say it's done pretty well. Again, thanks for all of the help and the suggestions. If it does anything else I will come back and ask.

 

I drove my Corsica again today and as hot and humid as it is here and with the ac running my temperature guage behaved itself. It did go to half and appeared to stay there for a minutes then went back down. I hope this means everyhthng is fixed.