Im having the same issue with a 1990 honda accord lx . i jumped the thermostat sensor with key on and the fan did not come on , but i jumped the cooling fan relay in the cluster box and the fan turned on . im reading in alot of post it might be a Fan Timer module ... any thoughts ?

 

On my 1995 Accord I was losing coolant which never left any signs of leakage and turned out it was the heater hose on the back of the engine below the leaking valve cover which ballooned the hose. It passed a pressure check up until the day the hose completely failed.

 

blocked line, thermostat, or water pump..

 

The heater hose sounds like a likely culprit. I'll check that when I replace my pressure sender.

 

Also, install the a/c condenser fan, because you need both to properly cool the radiator.

 

If you have a film that appears on the inside of your windshield with the windows up it could be a bad heater core leaking coolant.

 

Yep, definitely fogs up all the time, but it doesn't smell like coolant. Doesn't smell great though.