fans running on their own

[porsche newbie]

I have a 85.5 and every so often the fans will turn on as soon as I turn on the ignition before I even start the car. This happened a couple of weeks ago for the first time but only the one time and has been fine since. It happened again today and temp gauge was up about to about the 3/4 mark but never got any higher. Normally the temp gauge has been at about the 1/2 mark at the most. When I stopped the car and started up again about 15 min. later, no problem and the temp was coming back down. When I got home, the fans ran for a couple of minutes and shut off as normal. I went to start the car again and the fans were fine as always. Any suggestions because it is kind of hard to figure this out when it doesn't do it all of the time. I don't know if I am accomplishing anything or not. Temps have been in the 90's all week so maybe the car is just like everything else in this heat but any ideas?

[MKS_Performance]

What''s the mileage?

[Rasta Monsta]

Suspect fan relay.

[MKS_Performance]

^^^^^^

[porsche newbie]

mileage is about 104000.

[1982_928]

Fan switch, maybe?

[Chucked]

Clark's Garage has a detailed trouble shooting guide for the cooling fans and the fan relay. Check it out to avoid buying the wrong parts. The fan motor an fan relay are expensive.

[cauzomb]

agree'd with chucks suggestion.

A quick test, when you noticed the fans are stuck on, go out and try to unplug one of the thermoswitch wires at the radiator to see if the fans shut off, if they do not shut off then suspect the cooling fan relay/s

The thermoswitch is less expensive and in most casses available via your local autoparts store.. The major problem with the thermoswitch failing "closed circuit" is getting a dead battery..

When they don't turn on is what you don't want to happen.

If you disconnect the thermoswitch wire and both the fans are still running, suspect the fan relay, if one fan is on all the time, with the key on, and the thermofanswitch in the radiator unpluged, suspect the less than obvious AC relay.

[ernie9944]

Originally Posted by Chucked

Clark's Garage has a detailed trouble shooting guide for the cooling fans and the fan relay. Check it out to avoid buying the wrong parts. The fan motor an fan relay are expensive.

Link___ Clark's Garage Home Page enter Garage Shop Manual once on site & click on letter "T" .GL

[porsche newbie]

Previous owner gave me a box of assorted parts when I bought he car which happened to include a new fan relay. I swapped it and the problem has not happened again. It did not happen very often before so I am kind of wondering if this was the problem but time will tell. If it happens again then I will have to get more into checking the switch etc. Too hot to be messing with it today but thank you everyone for the helpful suggestions.

[1982_928]

On mine, the fans would come on sometimes when i put the battery cable on, and 100% of the time would be running and stay running after i ran it for any amount of time.. 5 minutes ago, i finished changing the fan switch in the radiator, hooked the fans up, started it, ran it for a minute or so, shut it off and they didnt come on. In my case it was the fan switch. Now to change the stuck thermostat......Ill have fun with that