1985 Corvette Electric Fan Problem

[netnarc2]

I have a question regarding the electric cooling fan on my '85 Corvette. I thought I'd ask in this forum first. My fan has always come on at 204 degrees and shut off at 196 degrees since I've owned it (2001). Now, for some reason it will come on at 204 degrees and it might just keep running or it might shut off at 180 degrees. Just today, when I started it at "LO" temperature after it sat all day, the fan came on. I turned the ignition on and off twice and it went off. I suspect that it's the sensor located on the right side of the engine block just behind the OIL dipstick, but I don't know for sure. If I let the fan continue to run all the time, will the fan motor me able to handle the load or will it burn out from over use? I don't know what quality these fan motors are.

 

[ecss]

I have a question regarding the electric cooling fan on my '85 Corvette. I thought I'd ask in this forum first. My fan has always come on at 204 degrees and shut off at 196 degrees since I've owned it (2001). Now, for some reason it will come on at 204 degrees and it might just keep running or it might shut off at 180 degrees. Just today, when I started it at "LO" temperature after it sat all day, the fan came on. I turned the ignition on and off twice and it went off. I suspect that it's the sensor located on the right side of the engine block just behind the OIL dipstick, but I don't know for sure. If I let the fan continue to run all the time, will the fan motor me able to handle the load or will it burn out from over use? I don't know what quality these fan motors are.

Sounds like you have two fans. The main fan is the one in back of the radiator near the engine. The auxiliary fan is the one in front of the AC condenser.

The main fan is controlled by the computer which monitors the engine coolant temperature sensor which is screwed into front edge of the intake manifold. The main fan on off temp. is stored in the Eprom which contains the engine calibration. The fan is also turned on by the ECM when the AC high pressure reaches around 240 psi and off around 180 psi.

The auxiliary fan is controlled by a fan switch located between spark plugs 6 and 8. If you turn the ignition On,
remove the Dark Green wire at the fan switch and ground it the auxiliary fan should run.

If you want to see the main fan run, take a piece of wire and short pin A to pin B on the diag. connector located above the drivers right knee. Turn the ignition On and the main fan should run.

 

[netnarc2]

This car only has one "main" fan so if it's controlled by the computer which reads the engine coolant temperature sensor and the temperature gauge says that the temperature is in normal operating range, why would the fan go on before it should? I'm not getting any messages on my dashboard screen and the temperature never goes above 204 degrees. When the temperature reaches 204 degrees the fan goes on. It used to shut off at 196 degrees but now it's anybody's guess when it will shut off.
Will the fan constantly running cause the fan motor to go bad?

 

[ecss]

Take a good look at the wiring for the fan relay. It's located on the back side of the driver side plastic wheel well housing below the front of the brake master cylinder. You should see four wires at the relay socket. Verify the wire insulation hasn't shrunk back allowing the wires to short together. Remove the relay and verify the relay socket pins are in good condition.

Red wire is 12 volts and hot at all times. This is the voltage that powers the fan motor.
Red/Black wire goes to the fan motor.
Dark Blue wire has 12 volts when the ignition switch is On. This voltage is used for the primary of the relay coil.
Dark Green/White wire is the control wire. The ECM grounds this wire which closes the relay and 12 volts from the Red wire is transferred thru the relay contacts to the Red/Black wire to power the fan motor.

The ECM will turn the fan on if certain error codes are set.
If you jump pin A to pin B on the diagnostic connector and turn the ignition On, the Service Engine Soon indicator will flash any ECM trouble codes.

You need a scan tool or scanner software to see what the reading from the ECT sensor is.

If you don't have them, all you can do is verify the sensor is not leaking coolant, and the two pin connector is in good condition. The ECT sensor is a thermistor and could be out of tolerance causing the temperature reported to the ECM to be off.

The connector has a Yellow wire and a Black wire. If you unplug the connector turn the ignition On, you should read 5 volts DC across the two wires at the connector. That's the reference voltage from the ECM.

To eliminate the AC fan switch which is mounted on the steel line going from the Condenser to the Evaporator l disconnect the two pin plug with two Black Wires. Take a piece of wire and short the two Black wires together. Start the engine and see if the Fan behaves normally.
***************Do not turn the AC on if you do this ********************

As for the fan running all the time anytime there is going to be wear on the bearings. It was not designed to operate all the time. No one can tell you how long it will last. If you manually spin the blades and the rotation is smooth there is nothing else you can check except the current draw from the motor.

I'd replace the fan relay (contacts could be sticking), the ECT sensor, the ECM in that order if you can't find the problem.

 

[netnarc2]

I'll give it a try. Thank you, everyone, for your advice.

 

[WhalePirot]

Early '85 fans were not controlled by the ECM, ala the '84s. The relay is identical to the O/D and FP relays for swapping/testing. I have seen sticky contacts not allowing a relay to open (had hook-shapes on the contacts, which a light filing removed).

 

[netnarc2]

Thank you. My problem is that when the fan comes on at 204 degrees it doesn't shut off like it used to at 196 degrees. I suppose a "sticky" relay could cause the contacts to stay closed, like the points on old style distributors. Another thing to check. I'm glad this is my "fun" car. One I can take my time working on that I don't have to rely on to drive to work.

 

[Hot Rod Roy]

Sounds to me like a sticky relay or sticky temp sensor to me, too. Any luck yet?

When the fan continues to run and the engine temp is below 180*, try disconnecting the temp sensor. If the fan keeps running, you have a relay problem. If the fan stops running, you have a sensor problem.

I presume you know that the fan is designed to run whenever you turn on the a/c.

 

[netnarc2]

Thanks Hot Rod Roy. It's been so hot here in CA that I haven't started to disassemble anything, although, when I tapped on the sensor which is located on the right side of the engine head, the fan motor shut off but came back on within a minute, with the engine temperature still low. Once the weather cools down a bit, I'll actually remove the device and see if it's the cause. If all else fails, it will go to the Corvette Shop here in town to let them solve it.