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Temperature Gauge Fluctuating

I have this recurrent problem with my 2002 Honda CRV. Last year my temperature gauge started acting up. It would remain at 1/2 mark after warming up but while driving it would sometimes go all the way to 0 and then come back up till 1/2 mark. It continued for some time and after a couple of weeks the check engine light came on with the error code P0118.

I then had the ECT sensor replaced. However after a few months the same behavior started with the temperature gauge and i again got the P0118 error code. This time i had the circuits checked at the dealership and everything seemed alright so i replaced my thermostat and also had the ECT temperature sensor replace (it was under warranty). This was a few weeks ago.

Now, since yesterday i am again seeing the temperature gauge fluctuating from 1/2 mark to 0 (cold). The check engine light hasn’t come on yet. Could someone please tell what is going on? I’m at my wits end with this recurring problem.

With engine cool, check the level of coolant in the radiator. Check the engine cooling fans. Do they begin to run when the temperature gauge is at the halfway mark, and stay on as the indication goes down?

I checked the engine coolant level and its just above the cold mark in the reservoir when engine is cold. Is there a way to check if the engine fan stays on when the temperature gauge goes down, since this only happens when i am driving and it stay down only for a few seconds.

It sounds like a simple sticky thermostat. Try replacing that for about $15+/- for starters.

Post back with the results.

I already had the thermostat replaced a few weeks back. The ECT sensor was replaced twice.

what climate do you live in? Have you had to top off the coolant recently? Did you add only coolant, instead of 50/50?

you don’t say whether this happens every time, or in different driving condition - city/hiway. so, Even tho it’s summer, try this. Start off and head toward a highway. Have the heat on HI, with the fan just enough ON so you can feel it. Then watch your gauge and air temp as the car warms up. the air should get warm in just a minute, before the gauge starts to rise. The, as the gauge rises, the heat will stabilize at HOT. then, if the gauge falls, what happens to the air temp?

Now, do the same thing from cold start in city driving, or just at idle in the driveway.

The difference might be that at highway speeds, the air blows hotter, but doesn’t at idle. This would mean air pocket in the coolant.

if the air blows the same in both schemes, but the gauge still falls, remove the thermostat, ad drill a small hole thru it, max 1/8". Yhis will allow a small amout of water to pass thru so that the radiator water will be warming up, and when the thermostat opens, the inrush of cold water will not be as severe.

Also, check the coolant bypass line. could be restricted.


Thank you very much for the diagnostic suggestions. I will definitely give it a try today as i intend to drive a fair distance. Regarding the climate, I live in san diego where the climate is fair almost all year long. As far as the frequency of the problem, it happens intermittently without any specific pattern. Also, what could explain the P0116 (engine coolant temperature circuit high voltage) error code that i received before?

The P0116 may indicate the cause of the problem. The code indicates that a wire from the engine coolant temperature sensor, is shorting to ground, or open, somewhere. Of course, “intermittent” means: sometimes. The engine computer, in response, turns on the engine cooling fans, to lower the reported hot engine coolant temperature.

Is it possible for you to check the coolant level in the radiator not just the resivoir? With all this thermostat work you have been doing I am thinking you are not filled correctly and have air trapped in the system

are the fluctuations immediate? and do you hear the cooling fans at the same time?

ECT could go bad again, but I am still leaning toward air in system.

top off coolant level just after starting car and fill overflow reservoir; replace rad cap then let it warm up in driveway and watch reservoir level.

The fluctuations are immediate in that it gradually moves from 1/2 way mark to cold and then gradually moves back up to 1/2 way mark. Right about the time when it starts going down I do hear the cooling fans kick in and the rpm gauge becomes hypersensitive (goes down toward 1000 when i lift my foot off the gas and when i step on the gas remains higher than it should). could you describe in detail the steps i need to follow to flush the air out of the system?

I can’t picture the CRV exactly. Start with cool engine. OK to be partly warmed up. Turn off engine. wait 5 minutes. remove radiator cap. restart and turn heat on HI. add coolant as needed. when full, and heat blasting, rev the engine to about 2000. if coolant level drops, add more. squeeze large radiator hose to burp them.
when coolant level holds, put cap on, top off recovery reservoir, and drive the car for about 10 mins. then let it cool for 5 mins and recheck level.

this should do it.

good luck.

Before i do this i want to report an observation i made. When i start with a cold engine and turn the AC to max, i see the cooling fans come on. However, after driving around town for about 20-25 minutes (without the AC on) i popped the hood and saw that cooling fans were not on. They came right on when i started the AC. Is this normal behavior?

Thanking you in advance.

Yes this is normal. When the A/C is ‘on’, both fans will come ‘on’. At least you know the fans will run.

Get to work bleeding the air out of this cooling system and I think that will cure the temp fluctuation problem. IIRC, Honda has bleed screws on the high spots of the engine to help you. So find out if you have one or more.

Well, it’s normal for the fans to run while A/C is on. You need to check the radiator, not the reservour.