Temperature gauge going up and down

The possibilities are: bad thermostat, bad radiator temp sensor, bad engine temp sensor, or air trapped in the system. Have you noticed if your cooling fans are engaging when the engine gets hot? If they are kicking on great, if not, that will add to the list of possibilities. Get back and let us know.

Yes Reelin, they are engaging and the A.C also works great to. Was also thinking maybe a sensor

I also forgot to mention that I have a check engine light for the swirl control valve, my mechanic looked at it and said it looked like someone tried to replace it and the wires were all messed up. would that have anything to do with it?

That's a plus! Have you or anyone else done any work to the cooling system? Like flushed it or replaced anything that would have required you to drain the system? If so, you may have an air issue. If not, I would try replacing the themostat. Very inexpensive place to start. Typically, if your radiator temp sensor is bad, your fans will not be kicking on when they should. If fans are working fine, I think you can rule the radiator temp sensor out.

Yeah I didn't do anything i just got it about 2 weeks ago, but we had checked the thermostat and it looked good my guy said so i don't know maybe its not

The swirl valve shouldn't affect your engine temp. It usually controls fuel mixture and burn.

Im am having somewhat of same issue. Why is it when i turn car off my fan continue to go for sec. Also as my temperature gage rises but car does not overheat. Do i have a bad thermostat or what? And oh i have to continously put power steering fluid. I have a chevy malibu maxx 07

Your fans will run for a short time after the engine is off. That's normal. If your temp needle gets up towards the red mark while you're driving, then yes, you may need to change out your thermostat. If it is at the half mark while driving, it's fine. As for the power steering fluid, you have a leak someplace. Could be the power steering pump. I would start looking under the car and locate the leak.

i have a 2006 Pontiac Grand prix and my temp. goes up to the beginnng of the red mark then back down to the middle.. whats wrong?

Hey, please let me know if u find out what it is. I have a 99 nissan maxima and it shows that my car is overheating but its not. I went to get an oil change recently and asked them to let me know if they see anything weird. I told them the situation and he was really nice and actually gave me a radiator flush for pretty cheap. He said if it wasnt that then it was most likely the thermostat. 2 weeks later, i just relpaced the thermostat and it is atil showing it is overheating but it isnt. I dont know what else to do, ive had 4 dif mecanics look at it so far. Please keep us updated (: lol thanks, good luckkkk!!!

Crzgrl637, change out the Engine Coolant Temperature sensor.

I had the same situation on my 99 maxima. I had replaced oem thermostat，engine temp sensor, gauge temperature sensor, new antifreeze,new cooling fans and fans relay too . But still nothing different. finally! one of Nissan tech guy told me. I have to press auto button on climate control. Otherwise the cooling fans won't kick on then you will see gauge over heat. There had a Econ button on climate control too. It is for winter , I mean heating. If you don't turn on your climate control the cooling fans won't on. Once your stop at traffic light in summer. Your will see temperature raise up.

does anybody know what can I do to fix it

is your thermostat working perfectly? Sometime the thermostat is stuck all opening or closing all the time. If you did tested thermostat ,It still happened. Try to startup the car and press auto button on climate control and check both radiator cooling fans are turned on or not. If both are on. It maybe something wrong with your cluster temperature gauge. Try to find one on eBay and replace it. ( to check your thermostat. Your can take out the thermostat and you will see a spring side at the back. Then burn it with torch gun or lighter or oven. Let see it moves or not. If the perfectly one u can see it opens with heated up , when you spray cold water on it. It will close ).

I have an 89 cutlass supreme international n my temp gauge goes up and down constantly I flushed the line and fans are working whats the next plan oh car is over heating n bought new radiator cap last one was leaking

Car isn't over heating typo

I would change out the thermostat. Post back with results.

we changed the thermostat and still shows its overheating. but the engine isnt hot to touch. we pretty much r feeding it engine coolant cuz it keeps eating it up...still noone can diagnose the actual issue...

I have a 96 geo metro. Noticed today that the temp gauge goes up right before my car shifts. Would this be related

Chris, check your coolant levels. Make sure your fans are kicking on when car is at temperature or when you turn on your A/C. Lastly, replace your thermostat. If after doing that, and it still seems to be heating up, post back.

Heater core and; a thermostat and possibly using the wrong type of Coolant there......

I have Santro 2007. Radiator fan is auto. I recently changed radioator, relay and thermostat. I am facing a problem. On or above 4th gear, and in standing position temperature gauge remains in center. But in lower gears (1st, 2nd, 3rd), temperatures gauge rises up between half and end marks, but the rad fan does not run, neither it does heated up. Can anybody tell me why temp gauge goes so up? I am worried.

Imran, there are a couple of possibilities. You may have air trapped in the system. Sometimes when changing out the radiator and draining the coolant, air can get trapped in the system which will cause an overheat. Or your ECT or Engine Coolant Temp sensor may be bad. Try and unhook the wire from the top of the ECT. The cooling fan should turn on. If not, check the wiring harness, relay, for shorts.

Ok I have an 03 accord ex 3.0 and my temp gauge goes up to about halfway I lose heat then it drops back to normal and I get heat back. Only does it once in a blue and randomly. Any ideas?

Tim, I would change out your thermostat. Your temp gauge should always be at the midway range. You may have a heater control valve that is not working properly. It may be closing on you and not letting in more hot fluid once the fluid in the core has cooled. Once the engine has reached it's full operating temperature, you should not lose heat. There should always be a constant flow of hot fluid going from the engine to the heater core. So either your heat valve is faulty or your core could be plugging up. Since it only happens once in a while, I would lean more towards a bad heater valve.

This is an old post. Sadly bryan never came back to tell us what happened with his ride. Regardless im having a similar issue, in that my temperature guage will go up to hot or so and sometimes red and stay there. I have coolant and i literally just spent 300+ replacing my thermostat and radiator.

Funny cause the car stopped having this problem. Fast forward two weeks and now im having the same problem.

Satokomi, did you try pushing in the climate control button like Evin suggested in the above post? He said that you have to leave the climate control on AUTO for it to run at the correct temp. Give that a try. Post back with results.

My car is an old car it doesnt have that feature. However. I think the head gasket is actually going.. The engine makes a knocking sound at the bottom. No milky residue in the oil and my fans dont spin when my air conditioning is off. My check engine light came on yesterday.

However the mechanic that checked it.. I believe he may be lying to get himself 2k from me.

If it's making an internal knock sound at the bottom, you may have bigger issues than a head gasket. The mechanic should have done a compression test and or a leak down test to see if you truly do have a bad head gasket. If he did not do those tests to confirm, then he may just be fishing.

The problem is fixed such that its sensor was not properly fit. The mechanic readjusted it and its not heating now.

Its funny you say that but the other guys i took it too told me they cant find anything wrong with it. So idk.

Ill go get those tests done

Turns out its leaking coolant and oil so imma have to get those repaired or find out where

Quick question, I have a 2006 Ford Fusion and as I drive it the temp gauge get to the middle range then slowly creeps up, then falls back a little and it repeats until it gets to the hot and stays. About 9 months ago the thermostat was replaced and I'm hoping I don't have a spend another 500 on this. Any ideas what it might be?

Tyler, I hope it wasn't just a thermostat that they replaced for $500! There are numerous things that can make your temp sensor creep towards the red zone. Low coolant, bad radiator cap, bad ECT sensor, fans not kicking on, head gasket going bad, plugged radiator, just to name a few. First check your fluid levels. Then make sure that your cooling fans are kicking on when the car gets to operating temp. Feel the top radiator hose when car is warmed up. It should feel very hard and pressurized. If not, you may have a bad cap. If fluid looks dirty or rust colored, then you may have a plugged radiator. You can try to replace the ECT sensor yourself. It should be located by the thermostat housing. Pretty easy job. Post back with results.....

Yea my fans werent kicking on. Replaced my radiator but my oil pump and water pumps were leaking and causing my to lose coolant and oil so my guage started going really hot . spark plugs were corroded car on mileage so i had to do the timing belt with cam seals and stuff anyway so i knocked it out one time. Luckily no head gasket damage

Well hope you got it fixed after all that! Is it back up and running?

My car is also having an issue. I just changed my radiator and my coolant thermostat sensor and my temp gauge still goes up. I had to replace my radiator because the first time I let me temp gauge go up and stay there it blew out the top of the radiator and caused a crack in the plastic trim of it. Now when I drive it the temp gets to the middle and slowly creeps its way to red zone and sometimes goes back to the middle or cold area. Then keeps getting hotter until it's in the red zone and idk what to do about it

Yea its running reeling. Turns out alot of maintenance needed to be done due to it having high mileage but the main reason was my thermostat Appearantly wasnt working properly in the model car so i got a new one the part mighta been bad i had to get stuf don hough epecially spark plugs cause they wwre corroding

I have a similar problem with a false overheating but with odd details. My 2010 Camry starts fine and when idling the temp gauge is in the middle. When I have been driving it will occasionally spike into the red for 30 seconds and then rapidly drop back to normal over 3-4 seconds. This happens about every 5-10 minutes. One odd thing is that if I have been driving for a while and come to a stoplight, it will stay in the normal zone but quickly rise as I accelerate away from the light. I have drained the radiator (not flushed), replaced the thermostat (old one appeared to be fine), and replaced the radiator cap (old one appeared to be fine). None of these have helped. I am not losing antifreeze and all other aspects of the car are in good repair. I was thinking of replacing the engine coolant temperature sensor next, but this is just shooting in the dark. Any ideas?

Mike and 97Integra, Have you noticed if your cooling fans are coming on when the car gets to operating temperature or when you turn on the A/C?

Found out my problem. It was my Ecu malfunctioning that caused my radiator to burst in the first place. Once I replaced my radiator and engine cooling sensor the problem was still there. Them I reset my ecu and all my problems went away

The fans do turn on when it is idling in the garage. I have not checked this on the road. I will also try resetting ECU. I saw two methods on internet, pulling EFI fuse and disconnecting battery for a few min. Is one preferable?

I have a 2000 ford explorer xls and my temperature gage is reading its running hot but the motor itself is cool to the touch the antifreeze don't bubble from heat and no steam ....what is wrong ???? Would it be the thermastat??

Has antifreeze has oil although I just had to get the oil seal changed cause the old one was wore out

You may just have just have a bad temperature sending unit or a bad ECT (Engine Coolant Temp sensor). Post back with results.

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?

Z_Marshall, Have you tried resetting your ECU like in above posts? Seems like the only thing you haven't done.

My temp cycling appears fixed. I changed the engine coolant temperature sensor this weekend. While doing it I disconnected the battery to reset the ECU and cleaned the terminals. Not sure which was the actual problem. 2 days so far. My earlier attempts at radiator drain/refill, thermostat change and replacement of radiator cap didn't help. Thanks for the suggestions.

Dear Reelin68, Well i didn't actually reset the ECU , i am not sure if the battery was disconnected when they did all the replacements but i will go down my basement now and disconnect the battery for 5 min and see if it comes back . My mechanics is thinking after all we have done to find out the pb that maybe some pins in the ECU connectors might give a wrong value ( for reference i had a similar pb with my esp light that was coming on each time i was taking a bumpy road and it was some pins in the connector socket of the master ECU). But this shit is really tricky i hope that resetting the ECU by disconnecting the battery will solve the problem . Thank god i have always a 13 in my glove box :P . If you are interested i will list here later all the parts i have changed on my car which is almost everything . The previous owner was a monster and cheated me when he sold me the car and as an s6 lover i basically changed everything to new. So i hope that the pb will be sorted soon , i dont want to damage my baby. Love that car so much the v10 is the most amazing engine for me and its sound is just a sweet song to my ears ! Thank you for the answer it means a lot to me .

Reelin68 Problem sorted for now by resetting the ECU after having disconnected the battery . I ve driven around 50 km since yesterday and no fluctuation of the crazy temp gauge , it stays at 90 and my fans are doing their job properly .

Good to hear! Glad you finally got her back up and running the roads! And this time it didn't cost you a penny at the shop! ;)

Reelin68 Bro , it happened again , just after washing the car i feel like my ECU connector might let the sand or water going in i will check all that Thursday and i will keep you posted.

I have heard of that being a common issue with other Euro cars. That was a problem with the older VW cabriolets. The seals would get cracked and leak water onto the computer or fuse boxes shorting everything out. Keep us posted.......

I have a 2001 Chevy Malibu almost same situation so today I drove my car on my way to my destination the temp was going up as I drove fast it would go back down but at stop light it would go back up on my way back it just stood going up so I had to stop various times no leaking water or anything though I have a new radiator and today my mechanic just put a new thermostat and a temperature sensor idk what can it be ?????

Jessica, if you have a new radiator, thermostat and temp sensor, the other possibilities could be that your fans aren't kicking on or you have a bad radiator cap. The next time you drive it and the temp gets to the mid range, pop your hood and watch to see if the fans kick on. If not, you may have a bad relay or fuse. The fans should also come on as soon as you turn on your A/C.

Jessica , i agree with Reelin68 but i will just add on remark , be very careful with the over hitting because it can cause severe damages to your engine and it maybe necessary after that to change your engine gasket joint. That over hitting on my car is very specific and we haven't still find out what was causing it , said so we have completely dismantled the engine this time and discovered that something was wrong with the engine timing so , after all the test came back negative for cracks, block included we have to put it back together and hope for the best. Good luck with your problem , it can be also caused by some sediment deposits in your pipes who could block your waterpump , or simply some air stuck in your cooling system when they replaced the thermostat if they didn't bleed properly the system. Keep us posted . Kind regards to all of you

Hi guys. I also have a problem with the temperature going high. I have Buick Century 2002. First thing that I did was changing a pipe where the antifreeze was leaking, then they took the air out of the cooling system, changed the water pump, fixed the hose, flush the system, fixed the fan. I don't really believe the mechanic where I used to go so I don't know how well he did all this... When the temperature starts going high the heat is not working and also when it reaches to red the car is not going more than 20 and the engine changes the sound( this scares me..) what should I do? Thanks

Adrijana if your temperature went into the red while you were driving you have probably damaged your engine severely , to make sure of that i will ask you some questions : Did you noticed if your cooling liquid was boiling ? Or any lick under the car ? Are you sure that it was a real overheating of your engine? FOR EXAMPLE : if your car stays with the temperature sensor in the red and going down very slowly for hours well then its a real overheating of your engine and you are going to face some couple of weeks without your car if you choose to repair it. The mechanics is going to have to open your engine and replace whatever part damaged by the overheat and run several tests on your cylinder heads and maybe your full engine block. As well, when the temperature goes in the red did you switch your engine off? if yes how long did you have to wait until the temperature goes down to normal? i am asking you this because if you have to wait just a few min for the temperature to go back to normal (90 Celsius degrees) then it might be something else that is overheating and goes back to normal when the car is stopped. Said so with the information you gave us , and if your engine "changed the sound" as you said well to that sound like your overheated your engine and it lost compression in the combustion chambers , so i don't want to scare you but to me this sounds really bad. The overheat probably ruined your gasket joint which is not letting the air from the combustion chambers mixing with your cooling liquid and probably getting into the system which would cause your engine not to cool properly, regarding the sound changing and loss of power this looks bad because it tells me that your piston rings might not do their work properly and this might result but a big loss of power when the engine is hot and a different sound . i hope this will help you .

Adrijana, first thing to do is change mechanics! Those clowns should not have sent you home with the car still over heating. A simple test drive would have shown them that the problem wasn't fixed. Tell your new mechanic to run a test for a bad head gasket like Z_Marshal suggested. That may be your actual problem. If it passes the test, the mechanic will know to test for other things. Such as a bad ECT sensor, radiator cap and so on. But like you said before, who knows what that other mechanic really did for work? It sounds like if all of the things were done that you say were done, there can really only be a couple of possibilities. Head gasket, ECT sensor, radiator cap, or bad fan relays. Keep us posted and good luck!

Hi guys. Thank you for replying back and for your help. I don't know anything about cars and most of the things you say guys I don't understand but I will try to answer the questions. The temperature goes back to normal very fast, it's going up and down. The engine changes the sound only when the needle goes to the red and is like deep sound and the car is not going more than 10-20. After that I stop the car and it needs few minutes after that all is back to normal but if I continue to drive it's happening all over again. I have noticed that when I put the heat on high the temperature stays normal. Yesterday I did so and even I had to start driving the car and right away it went back to normal. This morning too when I saw it is going high I turn on the heat and everything went back normal. I have noticed also that when I have the A/C on the temperature is going little higher. I have noticed leaks before but the mechanic fixed it. Whenever I went to the mechanic he would fill the coolant up and it would be fine for a little time. Also the security light is going on and off I don't know if it has anything to do with this.

Hi -- this appears to be a common problem - I have a 99 accord V6, it recently started running hot during traffic, cools of when driving. It is hitting the red on the temp. The fans are working because they keep running for some time after I turn the car off, so I believe it is really getting hot, not a false reading. The radiator is full. Have not changed the thermostat or any sensors, I wanted to know what is the correct or best order of things to do starting with the most likely? I don't want to randomly start changing parts and paying lots of $$ for no results. I don't trust ANY mechanics, thy are all cheats where I live in NYC. I would really appreciate any suggestions on what to do and in what order.

I would first change out the thermostat. Cheapest part and easy to change out. If car continues to over heat, I would buy a block tester at the auto store and test for a bad head gasket. Here's a short video. https://www.youtube.com/watch?v=CHp5E7XnbXo

thanks Mark. Will do the thermostat this weekend; I just put on a new radiator cap -- no luck. Hopefully the thermostat will do the trick.

TO : emazz , As Reelin68 suggested , you should go for the thermostat and get it replaced , if it doesn't work you can do as well a pressure test (picture bellow) of your cooling system in any mechanic shop or if you don't trust them you can probably buy a kit for a couple of hundred bucks and do it yourself. if the pressure goes down when you do the test : you have a leak somewhere. It can be an internal lick such as a blown gasket joint and you wont see any sign outside the engine , but maybe you coud open your engine oil cap (where you refil oil) and check if there is any sign of a white deposit looking like "mayonnaise". If there is some white deposit in that area : your gasket is blown. ( depending of how long you ride your car with the gasket blown you might see a little or a lot of deposit. if you dont see any , this doesnt mean that your gasket isnt blown specially if your problem appeared only few days ago you might not see any deposit at all . I kindly remind you that if you dont know what you are doing it would be better to go to your dealer or to ask to any of your friends for a good and trustworthy mechanic , i am sure that there is some in NY :) Good luck i hope this will help you .

@Reelin68 my temp gauge was rising to hot, ac stop blowing cold.... So I had my mechanic to replace my radiator..... Temp Gauge still floats back n forth, n it still seems as if my antifreeze leaks. Went to auto zone & tech stated to run water in the radiator to check for leaks in the hoses. Also the antifreeze reserve chamber was bubbling, could the water pump be going bad as the tech stated?

Ceasar42, if your anti freeze reserve was bubbling up, this means that your radiator is boiling over due to the fact the your thermostat is not opening. Have your replaced your thermostat yet? If your water pump was bad, it should be leaking around your water pump or from the weep hole at the base of it. What was the final diagnosis from Auto Zone? Also, what is the year and engine size of your car?

Hi I, This is Santhosh from India, I own a hyundai i10 2009, edition, my car engine heats up and the temperature comes to half way within 1 or 2kms, and sticks there, not going higher, from half way. Even if I drive for 50kms, the temp gauge will still be in half. Whether this indicates any problem to be arising, or I can trust my car and take a long trip say 500 mms. Please help me out

Dear Santhosh , what do you mean by "half way" ? on any car the temperature shall be around 90 degrees celsius when hot. Anything higher than this can damage your engine. Please be more accurate if you want us to try to help you. Regards .

Thank U Marshall for Your quick reply, here in India the temperature gauge in most of the car will be from C to H my car's temperature comes in middle of C and H within 10 minutes of drive..I have replaced the radiator and radiator Cooling fan motor, a couple of month ago. Tnx in advance Marshall

Santosh, that's perfectly fine. Most all cars stay at the halfway mark. You shouldn't worry unless it starts creeping up into the red zone. That usually is an indication that your thermostat is failing.

Thank You Reelin, planned for a long trip tomorrow, will update the status of my car, after that.

Travelled 250 miles, but the temperature needle didn't crossed the half way mark of C to H..

That's what you want. For example: C I IIIH Your needle should be right where the mark in the middle is. The 3 lines before the H are the red zone markers. If your needle is dead center between the C and H like in the above example, that is normal.

Yah Reelin dats wat I want it from my car, the needle is exactly at the dead centre between C and H, though I faced heavy traffic it didn't creeper towards H. This thread actually educated me in understanding the car's heating problem to the next level, Thank You Reelin, Keep gng..

Any suggestions for enhancing my i10's mileage, oil/petrol additives. Tnx in advance Reelin

I have a weird problem. When my check engine lights turn on, my temp gauge reads fine, on the halfway mark. But when the check engine lights is off, the temp gauge goes up a little pass halfway mark. What is going on? Before this happened, I worked on the timing belt, replaced the water pump and thermostat. could it be the thermostat that is causing this weird readings? what about the check engine lights? Thanks.

Lee, I would bring it to an Autozone and have the error codes read. Check engine lights don't usually come on for a short time then go off. They usually stay on until the problem is fixed. Double check your ECT connections next to your thermostat. Almost sounds like something is loose.

Can AutoZone check it

My cars heat goes on n off...thermostat goes way up...overheated one time....Been drivin it....engine lite stays on ....knocking noise when I turn car off...I put oil n antifreeze.....seems like it goes through lot of antifreeze.....had New thermostat n cleaning of catalyc converter not too long ago......is it really serious?

Thank you so much...that's a start

Hello, So I have a 2005 Infinity G35 and my car has THIS..... same problem and it does not sound like anyone has been able to fix it yet from reading all of these replies. mostly when I am stopped it randomly goes up and down but not overheats, not liquid boiling and AC if fine since May. I have had everything replaced you name it done. My mechanic actually gave me a complimentary rental for 2 weeks to work on this and determined that it was the bleeder/heater hose that had a tiny leak, replaced this and it was perfect for about 2 months. Reading over this info the only thing different is that I just had a new battery replaced last week and maybe it set something off and has to be reset?! I hate having this issue and it freaks me out seeing the gauge go high. I refuse to drive my car and luckily my husband has switched with me.

So I had my mechanic re reset the computer system and clear out all of the codes because I had my battery just replaced and this undid what has been working. So far I am very happy to report that the gauge has been perfect! I believe and I hope this is the answer to reset the system and clear out any codes.

I have 2000 cheve Malibu just had a radiator put in but my temperature gauge hand goes to red zone slowly but not running hot or leaking is a new thermostat in what could it be

i have a 2003 mini R50 I drove up the road was driving for about 20 min I noticed my temp gauge was all the way up and is usually half way checked under the bonnet everything looked normal no leaks on the floor.jumped bk in started the car the temp gauge was half way so I drove down the road parked up switched the car off started it bk up the temp was half way so I let the car run for 20 mins and it was running normal fan kicking in as normal what would cause the temp gauge to rise like that

GuruWlk4h, This took me forever, many mechanic shop trips, scared I was going to get stuck and time to figure this out. I determined that the codes needed to be reset. I had my battery changed and it undid everything. I had it reset after months of this and it was fine ever since. I did get rid of my car shortly after this because it was old. I had an infinity G35. Good Luck!!

I have a chevy Silverado 2003 1500 V8 Truck...I changed the thermostat and flushed the cooling system as my thermostat needle was going low and to the 210 normal mark. My fans came on before and come on now and the engine does not get hot. Now again my thermostat last night going low to 160 and up to the 210 mark but never over. Then again this am. I am trying to warm my engine as this is an older vehicle but I take very good care of replacing and fixing every problem this truck has. Hellllllp

I had this same problem. The vehicle was also slowly leaking antifreeze and no coolant was being pulled from the reserve tank. The temperature would go up all the way up to high, after a couple of miles of driving, it would sit there for about a minute, then drop to midway for the rest of the trip. I chased down all of my heater hose clamps and found a loose clamp (although a bad leaky hose will cause the same problem). After tightening up the hose clamp all the problems went away. The theory is that after everything cools down, air is sucked into your cooling system at the loose hose clamp. When you start driving again an air pocket is causing your temperature to jump up until the thermostat allows the coolant to flow again.