Non-Stop Fan

A while back I got my oil changed and the place forgot to put my radiator cap back on. The radiator overflowed shortly thereafter, and ever since then when I drive for an extended period of time, or if it is really hot out, my car’s fan will stay on after I shut the car off. It stays on even when the engine is ice cold. It drains my battery and I constantly have to jump it. What’s the deal with the fan? Could it be a result of the radiator overflow or is there some other underlying problem?

There are a couple of possibilities. It could be that the fan relay is stuck closed. It also could be a failed fan temperature switch that is not openning or shorted wiring.

Depending on the make, year, model, engine size, etc. of the vehicle involved, it could be many other things like fan speed solid state module, the Body Control Module, etc. Best to have a automotive electrical technician have a look at it.

Follow the path of the spill. It may have gotten into harnesses or connections and the residue is causing continual contact. Disconnect the battery first, then un-plug and clean all the connectors you might assume got leaked upon even the relay, as suggested above, could be shorted by the spill.

You really should tell us the make and model of the vehicle. If it is a 30-year-old beater and you live in a warm climate, I would just install a switch.

Sorry, its a 1997 Toyota Corolla

Interesting; that was the problem on a Chevy Corsica 1993 prior to the fan failing and being replaced. Now I can’t get the fan to run at all. I’ve checked the power wiring and replaced the temperature sensor and the control relay, but still no luck. There has got to be something wrong with the relay control wires as I don’t see how it can be the computer itself and the car still run.

There is no spilled fluid near the relay, and besides, I replaced it. Perhaps the wire broke where it goes through the fire wall? Could it have shorted to ground there first? But I think there is a connector there.

I believe on your Corolla there is a thermal switch in the bottom radiator tank so make sure that switch is not stuck closed. If you disconnect the plug to that switch and the fan no longer runs, that is the problem. If the fan continues to run with the thermal switch disconnected, there is a relay that is activated by that switch so find it and see if its contacts are stuck closed. You might be able to jar the contacts open again but the best bet is to replace the relay.

Hope that helps.

Correction, I looked over my available information and I am probably wrong with what I related. I referenced a Camary wiring diagram of the same year. It shows that the temperature switch is closed until the tank temperature reaches the trip point which is around 199 degree F. Also the A/C high pressure switch opens the circuit also. When the fan relay is not energized current flows from the ‘hot on run’ supply to the fan. When the two previously mentioned switches are closed the relay is closed and the contact to the fan is opened. So if the current path to the coil of this relay is open, current is sent to the fan. There is a separate fuse for the control feed to this relay. But in my wiring diagram the ‘hot on run’ supply voltage to the contacts is interupted when the ignition key is turned to ‘off’. So the overflow of coolant may have created a current path so that the ‘hot on run’ is hot all the time.

If you have a Chilton or Haynes manual, see if you can find the circuitry for the fans. It may be different for the Corolla. If you want to stop the fan for the time being, pull the appropriate relay and install it when you are ready to drive. At least that will allow you to drive it until you get this fixed.

Reply when you find the culprit – I am interested in what it was.