My thermostat gauge in the car is going up and down, what could be the problem

If this is gradual and it get's hot while sitting in traffic, cooling when moving, or goes very hot after coming off the Interstate, then it's a "stuck open" (or possibly missing if previously owned) thermostat. Replace it and be happy it wasn't stuck closed. If the change is rather quick and jumps around the gauge for no apparent reason then it may be a faulty temperature sensor. If this is the case, replace it because it will put undue stress on an electrical cooling fan with frequent starting and stopping. Most likely a corroded and stuck-open thermostat.

My guess would be a temp sensor going bad. Have someone with a temperature gauge gun shoot the car and see if there are any hot spots in the area of the thermostat. The thermostat is cheap to replace, time is the only thing. It will require draining the coolant from the radiator, the removing the thermostat housing, usually two bolts. Some thermostats can be put in upside down, so pay attention to the arrows on the thermostat. The water should flow from the engine towards the radiator. The temp sensor I think is in the rear passenger side of the engine on top. Remove the wiring, and using a deep 1 1/16 socket remove it and replace it with a new one. If none of these work, see if anyone can hook up a second gauge to make sure the one on the dash is working correctly.

My thermostat is going up when I'm going then when I stop it goes down what could be the problem I done replace the temp. sensor .

Pam, your problem seems similar to the original question. If the engine's temperature will not stabilize around 160° to 180°, regardless of whether you are moving or not, this usually is caused by a stuck open thermostat, or a thermostat that was replaced incorrectly. One check you can do without unbolting anything, (ONLY DO THIS WITH A COLD ENGINE) is to remove the radiator cap, make sure the radiator is completely full, start your COLD engine and see if the water in the radiator begins to move immediately. I CANT STRESS ENOUGH TO ONLY DO THIS WITH A COLD ENGINE! REMOVING THE RADIATOR CAP ON A HOT ENGINE CAN CAUSE SERIOUS BURNS FROM BOILING WATER.- besides this check will not work on a hot engine. If the thermostat is working as it should you should not see moving water for a few minutes. If water begins circulating immediately inside the radiator then the thermostat needs to be replaced. There are a few other major problems that can make the engine temperature fluctuate as you describe like a blown head gasket or a cracked head. If you are sure the thermostat is working properly, and if you are not doing the work yourself, have a mechanic check your radiator for exhaust gasses with a "sniffer". You can also look for white smoke or steam in your exhaust. If either or both of these check positive then I'm afraid your problem is a little more expensive than a bad thermostat. Don't let anyone tell you that unless you have water in your oil you do not have a cracked head or blown head gasket. Neither have to necessarily allow water to flow into the oil, but can allow exhaust to pressurize the cooling system causing it to circulate improperly.

Dear all , i need help here , i am having the following problem : Temperature gauge goes up and down from 90 to 120 , completely randomly sometimes it doesn't happen and sometimes it does, no difference if i drive , or stand at a traffic light , or drive smooth or hit the road hard. My car is an aud s6 2007 model 5.2 V10 engine , radiators have been checked , flushed , and reconditioned perfectly, thermostat is brand new , temperature sensor is brand new , expansion tank is new too. Than problem occured after i had a blown gasket due to a malfunction of my thermostat couple of month ago. Gasket has been replaced at that time but after 600 hundred km without any issue , i am facing this constant problem of the temperature gauge going crazy and for whatever reason it comes from 90 steady up to 120 in about 30 to 40 seconds and then it comes back down while im still driving, and then all the cycle again , up and down up and down , sometimes more than 120 and soemtimes less. The engine is not over hitting , coolant is not boiling ,cooling system pipes are not hard and can be pressed bare hands. The system has been already bleed properly and filled back with a special vacuum to avoid any air in the system. Cylinder head have been checked by pressure test and have shown a perfect health condition , no cracks no damages . Cylinders have been checked the same way and are also in perfect condition , there is no air lick and no crossover in the system from the cylinder to the cooling. The only thing we are thinking about now is maybe the wiring system. As well please note that this problem has happen just after i had a severe overheating above 120 degrees due to the thermostat that was not working and which caused my fans to not properly cool my engine at a certain point and consequently overhitted the full engine ( cooland boiling) After than incident we were not aware that the gasket was blown and we just changed the thermostat. At that point the car was doing that up and down with the temperature gauge , so we replaced it , ..result was nothing changed it was still doing it again, so we thought of a problem such as air in the cooling system, so we did the bleeding and again nothing changed. Result : same problem , so we opened the engine and found the blown gasket , we thought that it was the cause and we replaced it . Result after 600 km , the shit happened again . Temp Gauge is going up and down again . Do you guys have any clue of what the fk is happening to my car?

You've mentioned just about everything that can make this happen; cracked head - blowing exhaust into the coolant lines; faulty temp sensor; bad electric fan; sticking thermostat (make sure the new thermostat is not put in backwards. A backwards thermostat can cause all kinds of symptoms from overheating to random temperature fluctuations ); etc. You mentioned the electrical system which actually can cause needle gauges to read incorrectly. If you can thump the gauge with your finger and cause the needle to jump to and remain at a different reading then suspect a loose or dirty connection at the back of the gauge. Turn on your lights and watch to see if the needle moves to a different position - if it does then there is probably insufficient voltage on the "+" terminal of the gauge, a bad ground at the gauge or a bad connection at the sensor - could even be caused by a weak battery or an alternator putting out less than 12 volts.

Dear CaptPkelly I sorted the problem out following the advice of one of the person on this forum which was to reset the ECU's by disconnecting the battery . So since yesterday the gauge stays steady at 90 and no fluctuation anymore . I will keep you posted and thank you for your answer and the advices .

Pfffffff the shitt happened again . I noticed that it happens when i after i race the car and when i slow down for example at a traffic light the gauge will start to co crazy . I reset again the ECU by disconnecting the battery , Thursday my mechanics will check the ECU connectors witch are probably responsible for that shit i think. Maybe some pins are loose and it would explain why it happens after racing the car due to the hit and vibrations .

It could be in the cooling system also. Is there a possibility of air in the system? Do you have a overflow bag and is it full after racing? The faster you run the engine, the hotter the engine gets. Is the radiator clear? Have you modified the engine? The more HP you have, the hotter the engine runs. Is it timing? Something may be causing the engine to overheat if it only happens when the engine works hard. Now by "racing" is this a sanctioned street race, race track or just having fun on highway Route 66? I'd check and make sure the timing works as it should at higher RPMs. Have your mech. do a coolant pressure test, timing test, and sensor check. If it only does this when you "race", than I'd roll out the temp sensor.

Dear califcarson , So the overheating is coming only after lets say using my car in a sport way ,( as it is meant to be ) using sport mode , in the normal streets not on a track , so basicaly , i am driving fast and an nothing will happen until i stop to a traffic light and then the temperature will start ti rise up to 120 degrees ! So i would stop y engine , and wait for 3 or 4 min and it wil come back to normal... then i will happen again and again...

Z_Marshall: This is a sure sign of a stuck open (or missing) thermostat, a weak water pump (but rare if the water pump is not leaking) or a heavily rusted radiator, or a bad fan switch if you have an electric radiator fan.

CaptPKelly but bro the thermostat is brand new, the water pump is brand new too , the radiator have been cleaned and checked and is 100 percent fully functional, and all my fans i can hear them and see them running properly when the car is hot... i just dont get it.. and the thing is the temperature will rise and then after switching off and on with a 2 or 3 min gap it will be back to 90 normal. And then it will do the same thing if i stop at a trafic light . it is happening only when i am in the traffic or stopped. i doesnt happen at high speed on the highway

Do you guys think that some weak piston rings could give a back pressure into the oil chamber and cause that overheat ?

If you can get your hands on a heat sensor, try to shoot the engine when it is doing this and find out where the hot spots on the engine is. That may help start your search for the causation. Have you pulled off your heads on the engine recently? If so did you put on new gaskets? Some gaskets are universal in the sense they fit several engines or set-ups. The water jackets on the motor / cylinder heads are different on some engines. Make sure the gaskets are not blocking a water hole. I had a friend that had constant overheating issues. We pulled the heads and the gaskets were blocking 12 water holes on each head. Poked the holes in the gaskets and problem solved. If you have not pulled the heads, that is something you can keep as a reminder if you do change gaskets. Have you checked the timing or checked if the ignition advances at high speed? I'd check the radiator for pressure into and out of the radiator to make sure there is no blockage. this is going to be a lot of work, but it is better than blowing an engine. Any parts replaced, even if new should be rechecked. Is the correct amount of antifreeze in the system? It would not be a bad idea to spend a few bucks and put in a different thermostat. It may be that you picked up a bad one. Little things that are so simple to fix can cause a lot of problems. When the car is at running temp, are the radiator hoses hard and solid or mussy? I know they are new, but something is not allowing water to flow fast enough to cool the engine. It sounds like either the thermostat is stuck open, or it was forgot to be put in.

Why not just disconnect the temp sensor to make the fans run full time? if the engine stays cool then you know its not internal but just faulty electronics.

Yes my moms car when she starts it up it goes to cold to little hot but when she turns her air off it goes down what can be the problem

For my problem with my audi s6 , we found the problem , after dismantling completely the engine , and fitting it back the problem was still here ! so we decided to try new injectors on the car , and guess what ? no more over hitting ! I cant believe that it was the injectors fuck my life.,.. after all this time chasing our tail ! So basicaly a lean mixture in the chambers creates overhitted exhaust gas and consequently some weird overhitting of the engine ! Specially that here in Dubai the Gas is not well refined injectors are subject to faster degradation. I hope this will help you guys ! So if your engine is shaking , and over hitting it means probably that you have injectors problems like i did !

have a 2004 toyota highlander, my temp gauge keeps going up and down, while my guess cooling motor runs all the time, not good with cars , can someone tell me what i need to do to fix this....??

It could be your temp sensor on the engine going bad. They do that. Also, make sure the connections are solid before tearing into it. If you put on a new sensor, and it still does it, it may be the gauge itself. Also check the coolant level. Low coolant will not flow evenly and heat up, expand and then flow cool coolant through. Look to see if there is moisture or sings of a fluid leak in the water pump. Are the radiator hoses hard or soft to the squeeze? Worn out hoses can expand and soon burst. Look at them when the engine is warm, and see if there is any expansion on them. When cool, squeeze them. They should be solid and not spongy. Weak hoses can also collapse blocking the flow of coolant. Here is the order to do your research. Check coolant level. check for signs of leaking on the water pump, and hoses. Check for weak hosing, Make sure the connection to the temp sensor is clean and solid. If it checks our fine, then either have a reading done to see if the computer will tell if the sensor is bad, or replace the sensor. If it is still fluctuating, it may be the gauge. Also make sure your radiator is clear of leaves, paper, plastic, rabbits or squirrels that can block the flow of air through the radiator. Are your electric fans working? That is another check. Have fun and good luck. I may be old school, but I don't understand what you mean by "guess cooling motor". Computer typo spelling correct? That also is agravating.

I have a 06 chevy silverado that I drove from AZ to CA n when we got to Los Angeles the temp gage started reading high. Car is running fine no check engine light on, gage reads steady n not jumping around. Added coolant n the temp went down but as the car is running it's going back up. Any advice as we need to drive back to AZ soon.

hey, i have a Chrysler Sebring 2004 and my temperature gauge keep every so often going from the middle line to the line under the middle line . I just put in a new sensor , but it still doing it .so what could I try next.

My temperature in my car goes from in the middle to the bottom when am driving what could be the problem

I have a 2004 Chevy impala and my car was running fine but all of a sudden the needle rise to the red so I pull over and let it cool then as I crank it up it went down but the I notice a rattling noise so as I pull over it had cut off started smoking tried to crank it up .it wouldn't what could be the problem. I just put a motor in it a radiator a thermostat

Water pump? Did you notice where the noise was coming from? Could be a bearing in the pump. Check the timing also as something like the cam may be off in timing. Did it run ugh before overheating? Could the noise be in the heads, like a broken valve spring or something there coming lose? If you get it started, listen for where the noise is coming from. Was the coolant fluid level where it should be? Any smell of antifreeze or leaks? Check under the water pump for liquid. If it overheated, perhaps the computer picked up a problem and cut the engine off until it is repaired or reset. Sounds like a trip to your friendly mech may be in order if you can't find the issue on a quick check. How long has the new engine been in? A rebuild, swap, or crate engine? Warranty on the engine? backyard mech or a certified garage? There is where to continue you adventure.

As soon as I start my car the temperature goes straight to hot and my panel reads engine hot ac off. Also when I turn the car off my fan comes on and stays on, turns itself off, then turns back on again for different amounts of time. Can someone please help?

Check your sensor. Sounds like a short in it. If that is not it, have someone check the computer for error readings.

I have a 98 cavalier. On the highway today it started to bog down, and rev. When it did this the temperature gauge went down.. it's been doing it for a while now I have tried many things to figure out what is causing it. I do have an leak in my fuel tank as well as an exhaust leak before the cata. It's almost like a vacuum in the motor it's at the point right now where the temperature gauge isn't moving when I put the key in the on position. It use to move to 90 when the car was hot with the key in that position.

It sound like your computer is trying to compensate for your issues. You fuel delivery needs to be sealed, and exhaust throws the OX sensors off the track. Long distance driving with a gas leeks, and exhaust leak can cause carbon dioxide poising inside the vehicle. Having it closed up for A/C or winter for heat is not safe. Get them fixed, and perhaps your computer will smooth everything out.

I just patched the leak in the exhaust.. but the fuel tank is going to have to wait till I have the funds.. I never drive with the windows up.. unless it's raining and even then I crack them.. safety isn't a worries for me.. as far as that goes.. I am a little worried about trying to replace the fuel tank.. I am not sure it will be worth it.. I just hit 270k on the car.. she has more then paid for her self.. but if the issue isn't the tank and exhaustleak then I'll be out a crap load of money. Sometimes I think she is ready for the Derby!!!

And thanks for the reply

My temp gauge shoots straight to hot when I start my car. On a digital display, it says hot coolant temp. I pop the hood, top of motor and backside of radiator is cool to touch. No bubbling in overflow. After a few minutes of idling radiator begins to get warm. I've replaced water pump, thermostat, bleed the system for air. I was told my 2 wire sensor does not control my temp gauge. I am having trouble locating the single wire sensor. I'm driving a 2005 Chevy Venture. Could this sensor be located on the radiator?

Ok.. so turns out it was the plug for the ETC. The wire inside the insulated covering had broken like a cheap pair of headphones. It would make a slight connection when the wire was moved. I only found this out because I used my multimeter to see if it was getting a constant 5 volts.. the power too the plug was but the ground kept cutting out.. giving my thurmast the reading that it was like -40'c ..put a new plug in place and coooool beans.. is all good now! Thanks for the help

Haha I said ETC.. I meant ECT engine coolant tempature sensor. If random overheat.. check the sensor is getting constant power.. if random over cooling check to see the sensor has constant ground.

@drew.. read my issue.. the two wire controls a lot more then just your thurmast

Same roblem with my 1999 Chevrolet Suburban. Temp guage goes up high, heat gets cool, then it comes back down to normal until I get on the highway and it starts again. I have noticed that when I turn the engine off, there is a gurgling sound coming from the engine. We've replaced the thermostat, sensor, checked the head gaskets. . . . and it's happening again. Any thoughts on the gurgling?

Susan, it sounds like your radiator hoses are in need of replacing. Under pressure they can collapse and restrict the flow of coolant. When the car is cold, see if they are soft and spongy when squeezed tightly. When driving temperature, look and see if they are bulging or collapsed. Also your radiator may need to be flushed if that is not the case with the hoses. Then check for dead squirrels, chipmunks or trash/leaves blocking the radiator. If you can, when overheating, take it to a garage that can shoot it with a temp gun to find the hot spots. Also is the coolant correct? Sometimes oil changing services add water, not water/antifreeze combo, and that may be some issue. But since you changed the thermostat, I can only assume you put in new coolant. Changing the head gaskets are only necessary if you notice leaks, or water in the oil. I hope someone didn't steal you wrong...

What would be the problem if your engine gets hot wont turn on untill the enging cools down help me out

First the sensor is telling the computer it is hot, so it will not start until it is cool. Second it is hot and it will not start until it is cool. third, something is making the engine hot A. No enough coolant B. low on ion and the bearings are starting to seise. C. the engine bearings are bad, and are creating friction making the engine work hard and get hot. m(major engine rebuild) That is my guess. First make sure the engine is indeed hot. Your fluid levels are clear, clean, and in proper amount for the car. It also would be a big help if you gave the make, model and year of the car and there miles you have on it.

Hi, I have an 88 C1500. When im driving down the freeway the temp reads around 200 but then it will bounce down to 150-160 then bounce back up and down. Ive replaced the Coolant Temp Sensor but its still doing it. Every other aspect of the cooling system seems fine Hoses arent spongy, no leaks etc.. Could the actual gauge on the dash be bad ? Or does this sound like a bad connection somewhere ? Thanks.

Jason, Right off hand it sounds like one of two things. Air in the system. Easy fix. Or thermostat is acting up. a very inexpensive fix. With an 88, it's time to replace the thermostat anyway. Make sure the coolant level is where it should be. By changing the sensor, you should have a good connection. The gauge can be tested also before tearing apart the C1500. Start with the least expensive and work into what is the issue. Make sure the radiator cap is good, clean and on tight. When is the last time the radiator was flushed? Have fun.

Thanks for the quick response John. Ive replaced the Thermo, Flushed and Bled the system 2 months ago. It could be Cap because the one I have on it the metal ring thats supposed to either let coolant from reservoir to radiator or vise versa is pretty flimsy, Although it does push and pull to the reservoir.

Jason. Sensors seem to be a large concern now for some reason. China making bad parts, or cost cutting makes poor products. On some treads here people have stated they have replaced the sensor three or for times until they got one that works. If your engine gets hot according to the gauge, stops and open the hood and if it is crackling, it is hot. But what you have told us, it sounds lie a blockage somewhere, and a thermostat can act that way. Air is the system also will cause fluctuations. The cooling system is quite simple, the only mechanical moving parts are the water pump, and thermostat. Good luck my friend.

Thanks for your help John, Ill investigate further once the weather warms up.

Hey John, So I took your advise today and checked under the hood and I think the Radiator has a blockage. The gauge was ready close to 220deg. The upper hose was hot but the bottom hose was barely luke warm. The Radiator itself was cool to the touch in most places only a few areas were hot, mainly around the top part of the Radiator. Gonna try to flush again and if still nothing, ill just buy a new one pretty cheap on the older trucks.

Jason, hope it works for you. Try when cold removing the radiator cap and see if there is movement in the radiator fluid. If part of the radiator is hot and the other part is cool to the touch, it does sound like a storage. In the older radiators, before good anti freeze, radiators were taken apart and "rodded" out. Pushing a copper or brass rod down the radiator looking lines to get out all the contaminates. So if you hear the saying, rodding out the radiator, that is what that means. Now they try with chemicals, and it sometimes does not alway work . Good find.

I have no idea what the issue could be, but I am going through coolant, so it must be a leak somewhere. The radiator has been replaced, the hoses, sensor. The gurgling still happens every day, and I have to keep the resevroir filled. I believe that's where the gurgling sound is coming from.

It is NOT about the coolant. If the thermostat is stuck CLOSED, do NOT drive your car. IF the temp gauge is fluctuating, do NOT drive your car. I followed along with the misinformation. It MIGHT be air bubbles. I put in coolant and the needle stayed normal. Meanwhile, my car was overheating. I saw bad info on the net like "the car is operable with a malfunctioning thermostat." If stuck closed,, um, NO, it fucking ISN'T. Use your gut feel instead of google or yahoo or anything else. Treat it as a serious thing...before it becomes a serious thing. My needle said normal in my 2007 Toyota. Meanwhile the head gasket was being blown. I could have save myself $3000.

The most likely cause of a temperature fluctuations is either a flauty temperature sending unit , air in cooling system or a defectective cooling fan . If the engine temperature is stable when driving at highway speed and temperature rises when idling or in traffic , the fan is the cause . At high speeds ram induction forces air through the radiator and cools the coolant . However at low speeds the cooling fan plays a bigger role .So if the fan is not spinning fast enough there will not be adequate air flowing through the radiator to cool the coolant .If a thermostat is defective it is 99% to be stuck closed which will cause overheating . Not temperature fluctaution . Trapped air in the cooling system can cause temperature fluctuation .

Car temp gauge goes to middle when car turn on what the problem

I changed my thermostat and when I sit in a long line then my gages start moving up to hot then when o get ready for go from the long line it will be back to normal so what can that be

I have a 2005 Chevy equinox wen I’m sitting at long line and wen I get ready to drive up my gages start moving back up off the hot to go to normal wat can that be I changed my thermostat already

So what can that be I already had changed my thermostat and I changed my resoviour and I had bleed my cooling it’s just fine it’s just now when I sit in along line that’s wen it tries to over heat until I press on the gas then it goes back down to normal

Soooo I’m currently in a Cold weather state. My cars thermostat is going up and down. I have a Mercedes 2014, so for example I was driving the temp was half way then went back down then up and down here and there as I was driving.. I put coolant and I do my transmission light now so I already know it’s gonna be bad but can someone can just help me out more...