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Honda Civic temp gauge fluctuations

I have a terrible car. Honda Civic 2002 that runs alright but quakes and shudders after I start it. It also revs up for no reason at all whilst I drive around. Anyway two machanics have told me I have a headgasket leak that will cost a lot of money to fix. Two others have told me I don’t or that it is so minor it needs not be messed with. The last one I saw decided I had a bad Coolant Sensor for the Computer. I guess there is one for the computer and one, um, not for the computer. I bought both sensors and he changed them Friday. Today I took the car out and three times while I was out, my temp gauge shot up into the red hovered for a few minutes and sank back down. It has never done this before. Does anyone have an idea why this might be happening now? I am really sick of taking my car in and getting a thousand different stories, paying to fix things that are not wrong with it and watching it die a slow death. Thanks for reading.

If you want to keep this car you need to find a really good mechanic and pay for the diagnostics to find the real problem. I don’t think there is such a thing as a minor head gasket leak. If it’s really overheating the engine will soon be ruined.


Are you losing coolant?

Has anybody performed . . .

coolant pressure test, including the cap
block test . . . if a mechanic doesn’t know this term, he’s not the one for you

As for the mechanics that said you have a headgasket leak . . . ask them how they determined this. Did they use a 5-gas analyzer to detect hc in the coolant? Did they do the block test I mentioned? If so, did the test fluid turn yellow when your car presumably failed the test?

Has anybody bothered to replace the thermostat?

Has anybody bothered to check if ALL of your electric fans are even coming on, and at the proper temperature, and under the right conditions

Well, and I will try not to sound like a complete moron but I really have very little knowledge of these things, the first two machanics ran some sort of dye through the engine and it changed colors thus their reasoning for a head gasket leak. The third machanic did a pressure test and said my car was only losing like one pound of air an hour so I was doing pretty good. The fourth one read the codes which said something along the lines of there being a coolant pressure something something so he replaced the sensors. Now, the oil and coolant do not mix, my car blows no smoke and the car doesn’t to overheat (yet). Nor do I lose much coolant from the reservoir.

No one has replaced the thermostat but this problem with it fluctuating literally began today.

Also the previous owner rewired the fan to run as soon as the car is turned on. It is all messed up in there. But the engine stays cooler that way so everyone is hesitant to fix that.


“ran some sort of dye through the engine and it changed colors . . .”

Sounds like they performed that block test I mentioned

“Nor do I lose much coolant from the reservoir.”

But you apparently ARE losing coolant, and can’t see any external leaks. Which makes the bad headgasket a very real possibility

“Also the previous owner rewired the fan to run as soon as the car is turned on.”

Translation, IMO . . . the previous owner was experiencing severe problems

If the headgasket is bad, and you decide to have that job done, you should also have the head resurfaced as necessary

Your symptoms are consistent with a head gasket failure on a Civic. My '03 Civic had all your symptoms and got a new head gasket at 150k miles 2 years ago. Been great since.

Hondas are VERY particular about their cooling systems…they do not like any air in the system. When you lose coolant from a leak or burn it from a head gasket…and then you simply top off with added coolant…you need to either Burp the system using the bleed nipple usually located by the T-stat housing…OR fill the overflow and allow the engine to go thru several Hot cold cycles…this will pull in the new coolant and burp air…but takes time.

When Hondas have an air bubble the temp gauge will fluctuate wildly…because the sensor is in an air pocket…and then it gets hit with hot or cold coolant semi randomly…so the temp needle swings all over…

In addition the AIC (Air Idle Control Valve) has coolant running thru it so the engine knows how to idle itself… Faster when cold…slower when warm. The air pocket screws up the Idle very often on Hondas…same situation…air and not solid coolant running thru the AIC Valve…so it gets confused…one moment its measuring air temp…the next a splash of hot or cold coolant so the idle is severely affected.

You need to fill your cooling system and either burp with a bleed nipple…or use the overflow and several hot and cold cycles.

If you suspect a head gasket failure…they can fail in many different ways. Sometimes the engine burns the coolant…which produces white puffy clouds out the tailpipe usually… Sometimes it can leak piston compression into the cooling system. When you run the vehicle pay close attention to the overflow bottle as well as the rad hose pressures… If your hoses are hard to the squeeze…it can indicate over pressurization and when this happens the rad cap releases coolant into the overflow…sort of in a pulsing manner.

You need to figure out where your coolant is going…its either on the ground or being burned…each have telltale signs.