Have a '00 Civic with JDM B18C, its been running fine with no issue for a year. That is until yesterday I drove a 90 mile round trip and upon coming home stopped at a gas station to refuel and noticed the temp temp gauge was normal than higher. So first thing popped the hood and see if the fan was coming on, it wasn't. So drove home and it would fluctuate up and down in the middle. Never overheated will say that. Today I checked the fuse, relay and nothing wrong. Replaced both coolant temp sensor and radiator fan switch and still same issue. OK I then checked the wires from the coolant temp sensor and fan switch for continuity to fuse box, ground and ecu. Everything checks out good, so does anyone have any insight regarding this. Only thing else I could think to be wrong would be the ecu.

 

Water pump ok?
Radiator clogged?

The fan spinning?
Fan relay ok?

 

Have you actually tested the fan itself yet ?

 

Yes already tested the fan directly to battery no issues, relay clicks when tested. Coolant seems to be flowing fine and both upper and lower hoses get hot so thermostat is opening.

 

So this morning I drove it to work no issues while on the highway which is normal, get off and my work is a minute off the highway. Stop in the parking lot and wait to see what happens, it starts to get hot so I shut it off. Put the key to the on position with engine off and the fan kicks on, I waited like 10 seconds. Then I turn the key off then back to the on position and nothing. OK, turn the car on and temp is hot but fan doesn't work so I immediately turn the car off. How does this possibly happen, I've been reviewing the wiring diagram for the circuit and it has me stumped.

 

OK so after I wrecked my brains out all morning long and thinking about how the fan cycled on after it was way past normal temp this morning. I though why not jump the fan switch connector and see if that works, well it does so that means my new fan switch from Autozone is calibrated to the incorrect temp reading. Which explains why the fan came on this morning but after is was way past normal. So as usual Autozone let's me down again, picking up an OEM one from my friend tonight. Lesson learned not all things are made equal aftermarket vs. OEM