My 2000 Honda Civic EX says it's overheating but it's not showing signs of overheating. Background story: water pump blew up inside case so we replaced it and the timing belt and thermostat. Car will not heat up while idling but after you drive it for about 1/2 hr., let it sit for about 20 mins. then drive it again, the gauge will go to red line. No signs of blown head gasket, fan works (we hardwired it so it runs all the time now) and after we got the car home from the red line trip, no signs that radiator was really hot...not spewing water...took the rad cap off right then and all was just fine. Could sensors be at fault? Wiring? Checked fuses and they seem to be ok. I believe we purged the air from the rad and timing is ok, thought maybe water pump parts got lodged in head causing blockage????? Please help....any ideas anyone??? What should I do next? Can't figure it out....try new sensors? Diagnostic? What??????? I desparately need my car, it's never done anything like this before now

 

Maybe the new thermostat isn't opening. Does turning on the heater reduce the engine temps?

 

Did you bleed the cooling system after you did all the work?

 

^

Bleeding the cooling system may take 20-30 minutes.

1) Park the car on an inclined driveway with the front end higher than the rear.

2) Push/turn the dash heater lever/**** to MAX heat. Fan need not be on.

3) Follow the directions in the diagram below

 

I don't like the fact that you hardwired the fan, now you will not be able to tell if it will overheat when idling or at highway speeds.

You need to see if it overheats at idle and driving or one or the other.

How old is the radiator? You might have a clogged radiator.

 

 

it heats up only when driving...not at idling at all. It's the original rad. How do I tell if it's plugged....appears to be working fine....water moving thru it. We hard wired the fan cuz it seemed that it was coming on intermittently.

 

 

it is my understanding that the rad had been purged of air but it wasn't done like you suggested....just run with cap off....I think I'm gonna try it again per your directions.

 

 

for a minute that worked then gauge started to climb again. yesterday we drove it for about 1/2hr., let it sit for about 1/2 hr. then drove it about 5 mi. I turned on A/C and was driving about 55 mph up slight incline. Temp gauge moved up fairly quickly....went to red line....pulled over, cooled down, drove again, heat up, pulled over, cool down (not to half way mark, just down some)...limped it home, no spurting water, took off rad cap, everything looked like normal....not really overheating....???? bad sensor????