First off, I have only seen this today. I was starting in on fixing my idle issue. I was just generally familiarizing myself with the engine bay and stuff (my first Honda), and I notice my coolant reservoir was empty except for just a small ounce of fluid. I have driven the car about 500 miles so far, and all the time the gauge reads slightly below middle.

So at this point, I stop with the idle issue troubleshooting and take the car over to walmart to get some coolant. And at this point, I see for the first time my temp gauge needle points directly at middle (used to point slightly lower than middle), and then it rises a bit to like 65% high. And then to like 80% high. And then drops all the sudden to a bit below 50% (normal for me). It would continually drop and rise but quick changes, not slow gradual ones.

Could unspinning the cap to look into the reservoir create an air bubble that could all the sudden make me have fluctuating temp gauge? This is the only thing I did and now have a moving temp gauge.

Could the fact that the needle moves fast be that the sensor is bad?

I notice also that when my car was warmed up (after my drive back from walmart) and with the engine on that the fan was not moving.

After I got back, I added my 50/50 mix of green walmart brand coolant and walgreens brand distilled water to the reservoir to meet the reservoir line. I turn the car on again after this, the temp gauge read 50% again (still higher than the usual 45% I had for first 500 miles of driving). I also check the level of coolant reservoir and it did not move.

 

Hey whats up? Yeah, I had the same issue on mine too. jumped on here and found out it was air pockets, just have to be careful with the coolant system. It can be a pain, there is a coolant bleed valve on the engine, just find it and try bleeding it and see if that helps out at all.