While attempting to diagnose the mysterious electrical gremlins that are causing my cars engine issues, I am also trying to figure out the odd behavior of my cooling fan. The fan usually (maybe 80-90% of the time) comes on immediately when the car is completely cold and the key is turned to the acc position. This indicates to me that maybe something is grounding the fan relay and keeping it on? however, the fan turns off after a few min and the car is warm. It stays off even to the point where the car sometimes starts to overheat if I dont pull over. Furthermore the fan stays off even if the car is turned off and restarted until the car cools off (a few hours later), at which point the fan kicks right back on again as soon as the key is turned.

would a bad sensor or something cause this backward (on when cold/off when hot) behavior?

The car is equipped with a single fan (although the airbag warning on the shroud indicates that something was pulled from another car as my 87 doesn't have airbags)

When all things are working the fan is adequate to keep my car cool so the overheating is not really my problem, I am trying to figure out what the deal with the fan is. As a side note, the fan appears to display this behavior irrespective of the position of the A/C switch.

 

My guess is that whoever retofitted the fan messed up the wiring. Check the relay and report which wire is going where, that should answer the question.

 

You may want to start with Reids post here: https://www.thirdgen.org/forums/cool...-diagrams.html

 

Just to update, it appears I may have resolved what the issue was. I noticed recently that my fan started behaving differently where it still came on when the car was first started but there was perhaps a week where the fan did not turn off when the car got hot. Then a few days ago it seems like it was hit or miss where sometimes turning the key started the fan and sometimes it didn't. This varying behavior led me to reexamine how the fan was hooked up. I started at the fan relay and traced the wires; the red and black went straight to the fan as it should; but the green wire that normally would eventually get to the coolant temp switch was grounded straight to the body!

It appears the PO did this to keep the fans on all the time so he completely removed the coolant temp wire from the system (I have no idea where the coolant temp wire goes now). I figured the erratic fan behavior was perhaps a bad relay (just a coincidence that it shut off when the car got hot?) so yesterday I replaced it, and since then, the fan comes on when the key is on (as the PO wired it to do). I will watch the fan's behavior going forward, and eventually when I go through this engine bay attempt to correct the wiring, but in the mean time can anyone think of any reason that I shouldn't keep the fans wired as such? I can't imagine anything would get messed up by doing this and the car is still getting up to operating temp.

 

Running the fan constantly is a waste of electricty, and therefore gas. Under real driving conditions, the fan will only run if the A/C is on or you are stuck in traffic. You are also burning out the fan motor.

 

You have two sensors. One on the drivers side, for your temp gauge in the car. there is one on the passenger side, right above your dip stick, that's the fan temperature switch. This tells the fan when to come on in a single fan set up. In a dual fan, this controlls when the second fan comes on. the primary fan being controlled by the ECM. The green wire should run through one of the relays on teh firewall (on the drives side) to the fan switch on the passenger side of the block (Should). If anyone else wants to chime in please do. I"ve got a single fan set up so the dual fan might be slightly different.