1998 Honda Civic



August, 7, 2009 AT 10:42 PM

Engine Cooling problem
1998 Honda Civic 4 cyl Two Wheel Drive Automatic 97000 miles

The radiator, radiator temperature cooling switch, and thermostat have been replaced. The coolant is new, and the engine oil doesn't have any water/coolant mixed in it. The radiator fan comes on, and cycles on and off when the engine is up to temperature. I'm assuming the water pump is okay also? There are no leaks I can see and and the coolant level is full in both the radiator and the reserve coolant tank. The coolant is 50% Prestone antifreeze and 50% water.

The problem is that the temperature still rises up close to the red line after about 15 minutes of driving in hot Tucson, Az summer weather. When the temperature starts to rise, we turn the air conditioner off and turn the heater on, then the temperature goes back to normal.

I haven't replaced/tested the coolant temperature sensor which provides an input to the PCU (powertrain control unit), as well as the dashboard temperature gauge. How can I know if the sensor is working properly thruout the temperature range?

Also, the service manual wiring diagrams show an output from the PCU that is wired in parallel with the radiator temperature cooling switch. Is this PCU output supposed to turn the radiator fan on after the car is turned and and the coolant temperature is still above a certain temperature? If so, how long is the radiator fan supposed to run after the car is turned off?


2 Answers



August, 9, 2009 AT 12:34 PM

The cooling fan turns on after a certain temperature. Once the temperature is below that specified temperature, it shuts off.

Have you had your engine leaktested? This will test your headgasket.



August, 18, 2009 AT 8:59 PM

Thanks for your help.

We found another post on another website, describing a similar problem for a 1991 Honda Civic. They replaced a lot of cooling system parts before they discovered the radiator fan was running backwards, and blowing air from the engine onto the radiator. They reversed the wiring for the fan, changing the fan direction, and their over heating problem was solved.

We reversed the wiring to the radiator fan also and our problem is now solved also (a 30 second fix). The car was bought used and the connector to the radiator motor was broken, which allowed the fan wiring to be connected backwards. We also noted that the air conditioner condenser fan is blowing air into the engine compartment, as it should, and now the radiator fan does the same thing. The service manual never mentioned air flow direction for the radiator fan; I'm guessing they assumed the polarized connector would prevent the wiring from being connected backwards!

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