For some weird reason my temp gauge is dropping and is reacting when I put the lights on. It's pretty random to be honest.

Idle the car and let it warm up, temp goes slowly up and then is set in the middle, going for a drive, temp gauge is still spot on.

Then out of nowhere my temp gauge is dropping and it set around the middle of the temp symbol and the C symbol, sits for a bit and then goes back to normal.

On the highway everything is normal, exit the highway and temp gauge drops a bit :S

What could it be?

Fan kicks in, no overheating, both rad hoses are warm ( 1 a bit more then the other) so thermostat is working? Switched the engine coolant sending unit for a different one no luck. engine coolant temperature sensor is working because the fan kicks on. Also bleed the system so no air in the system.

Got a D15Z6 with a ESI rad in it and the rest is stock

 

Post specific car information.

Did you mean D16Z6?







Have you properly and thoroughly bled the cooling system?

https://honda-tech.com/forums/honda-.../#post38664177

 

Nope.. I have a D15Z6 VTEC-E.

Yes, rad cap off, heater full heat, no fan on and just let it idle until the fan came on.

 

Fan must turn on twice. Does the D15Z6 have a bleeder valve?

 

Hmm... some say need to turn on twice and the other says 1 and it's good :S

No.. doesn't have a bleeder valve... need to bleed with the rad cap off

 

Rebleed using the service manual instructions I posted. If you don't have a bleeder valve, then just skip that step.

It may also help to raise the front end on jacks during the procedure.

 

Check your ground cables on the thermostat and on the valve cover for any signs of contamination or corrosion and clean the contacts

 

Did a test on the gauge and sending sensor today... couldn't do a check up on the ground points of the car because it was raining like crazy!

Gauge meter is working fine when I tested it, Sending sensor gives 240 ohm resistance with a cold engine.. Checked the service manual and it says it needs to be at 142 ohm but it's a bit vague because you can read 56 celsius but they say to check it with a cold engine :S


The ground point was de engine.. didn't got to test it when the engine is @ operating temperature

Could it be that I have a bad ground point somewhere?

 

The big wire from the battery (-) to the body and then to the engine is the most critical ground here. There is also a ground behind the instrument cluster that can make gauges go haywire. Of of course the cluster itself.