kipdo

Hello All. I went for a ride today, it is very hot here (106). Parked the car in the garage. My wife went out about an hour later and said your car is running. Sure enough the electric fan was running. I disconnected the fan, so the battery does not run down. Any suggestions what would cause this?. Thanks, Kip.

j.kenzie@sbcglobal.net

Model year?

kipdo

Sorry 86.5 5 speed

John Struthers

My 82. does the same. Only when hot.
I thought this was normal. As heat will build locally after shut down due to no circulation.
Guru's?
Don't make me look in the WSM's.

bigs

It's normal - designed for the reason John mentioned. Go back and hook up your fan again.

bgrabner

What bigs said - its unusual for the fans to run that long, but at 106 degrees, I'm not surprised. The fans will run with the car off until the engine temp is down to acceptable levels - if you disconnect them or open the hood (which causes them to shut off), you aren't allowing the cooling system to do its job. Hook them back up

Intrinsicate

Current temperature, here, is 113 degrees.

kipdo

Thanks for the info. What seemed odd was that the fan did not run when I shut the car off. Perhaps the temp rose after I shut the car off and caused the fan to come on. Thanks again. Kip

H2

I have an issue which I call "Ghost Fan" where my '85S 32v fan will turn on by itself a while after I park the car and run until the battery is flat. I replaced a zillion sensors it seems and was never ever able to fix this gremlin. The problem started after I had a mechanic do some work on the car. Finally, I just wired in a manual switch to bypass the problem. When it's really hot I flip the switch and the aux fan comes on. At some point, when I figure out where the problem is, I'll fix it.

This is no help to you but I'm interested in the responses too.

Harvey

Rich9928p

It is not normal for the fan to run for about an hour, regardless of the ambient temperature.

The 1987 928 S4 and newer models have two electric fans for radiator and A/C condensor cooling. There is an operating mode that will "briefly" run the fans after engine shut down to help cool things down. With our hot PHX summer temps I observe this nearly every day. But the fans don't run more than a few minutes - about an hour is much too long.

The 1986 and older 928s don't have full electric fan cooling, they use a crank driven pully powered viscous disk managed fan with a smaller aux. electric fan that fits in front of the condensor. For the 1985 model 928, the aux. fan control consists of (using the names on the wiring schematic)

- relay XVIII Aux. Sensor
- Thermo Switch (Intake pipe)
- Oil Temp Switch Torque Converter
- Thermo Switch cooling water
- Temperature regulator Freon

I would first test the Relay XVII to see if that is bad. If the realy is OK, you'd need to test the other switches.

The pre-1987 aux. fan control is completely different from the S4 and newer 928 radiator fan control.

pmotts

Thanks for the info, Rich. The longest any of my 928's fans ran after shutdown, even at the track, was a few minutes.

j.kenzie@sbcglobal.net

What Rich said sound right.
I think the XVII relay is a pretty standard type. The 85 terminal is grounded by any of the 4 sensor switches which close to ground under their design condition (too hot). I think you can swap relays and if that doesn't solve your problem, it sounds like you have an intermittant short to ground in the sensor wiring. Getting at the various wires is another thing.

bigs

OK. Upon further pondering, I'm gonna pose a question to the shark wrenches around here.

I can't imagine the purpose of the fan running intermittently after shutdown of the car is to cool the engine. Surely a few moments of the electric fan running wouldn't have any significant advantage in cooling the engine block - or structures deep inside the block.

Likewise, what would be the point in cooling whatever water is in the radiator? Without the water pump circulating it, what advantage would there be in simply having standing water within the radiator a few degrees cooler?

I'm wondering if the purpose isn't mainly to simply keep the temperature within the engine compartment a few degrees cooler to reduce long term wear, drying, and cracking of hoses, belts, plastic items, etc. under the hood.

Comments?

j.kenzie@sbcglobal.net

Hi bigs,
I think it's what you said in your last paragraph. The car becomes air-cooled until the radiator water temp sensor says it's cooled down enough. Might extend the life of rubber, wiring and mixed metal connections.

H2

Bigs,

I've wondered about that too. I know the 928s run hot and maybe after shut off the fan just keeps the engine bay from getting all the hotter from residual block heat by keeping a slight breeze going?

Harvey