My 2000 Civic Ex Coupe with 94xxx miles, keeps overheating. It has overheated on me 3 times recently, the first time I was on the freeway when a bottle neck caused a slow down, after about 10 mins in traffic and staying in 1st or 2nd gear I suddenly noticed that the temp gauge was at 3/4, I blasted the heater and the temp came down. I checked the coolant when I got home and it was fine. The 2nd time, I was driving in a parking garage and noticed the gauge climbing, cranked the heater and parked the car soon after. The 3rd time, the car was just idling on a hot day when the gauge got to 3/4 again before I realized it, this time I checked under the hood before turning it off. I noticed the A/C fan turns on, but the coolant fan never turned on.

Also, driving the car above 30 mph the gauge stays at its normal place and doesn't overheat, not even on the freeway when the RPMs are running high.

Today, I manually powered the coolant fan and it works, I checked the fuses and they are fine, the coolant relay also works.

I don't know what else it could be. Any advice?

 

Did you check the coolant temp sending probe?

 

Hello,
I agree with maachan513 the fan is not getting the signal to turn on. Check that engine temp sensor and the wires on that are on it. The overheating problem is the worst thing for an engine and it can cause major problems.To find the problem can be a easy one or a pain in the you know what. The cooling system problem checklist, Fans are working, the themostat is working, the waterpump is working, the system has no leaks, the rad. is working, not clogged. The worst is a bad head gasket or cracked head. One way to checked for a bad head gasket is to pull the plugs and see if any of them look real clean, due to the water getting in and steam cleaning them. Hope you solve the problem. Keep us posted we all like to know how the problem was solved, to help other members on this site. Thanks, 2010civiclx

 

The fan thermal switch is on the thermostat housing where the lower radiator hose meets the engine. Unplug it and jump the pins in the plug. The fan should now come on as soon as you turn the key on. You can test drive like that and confirm there's no overheating, if that resolves it, replace the switch.

 

Just got home will check over the weekend and keep you guys posted. Thanks for the tips.

 

So I think I have fixed it. I had to change out the coolant fan switch that is mounted in the thermostat housing. It's was $20 @ AutoZone and now the radiator fan turns on when the engine temp reads precisely 205 degrees.