Radiator cooling fan non operation.

[Betared]

This is a strange one and "doing my head in " to coin a phrase. While setting up the slow running after a carb rebuild on my '83 Coupe the pressure cap on the expansion bottle started to lift advising me the temp was too high and at the same time that the fan hadn't kicked in. Looking for a cause I found that the feed to the fan is via a single blue wire that goes thru the rad. thermoswitch and the fan to earth. Now the wiring diagram shows the blue wire feeding the fan and a white/black wire connected to the thermo switch. When the switch closes it completes the solenoid switch operating circuit and allows fan feed circuit to complete and the fan to run.As I've said I only have the blue feed so am at a loss to understand how the fan can run!! Can anyone throw light on this one?
David.

[Neil-yaj396]

I have had lots of problems with dead thermoswitches. My immediate recollection, without looking, is that the two wires from the switch go back into the loom, but I'd have to check.

Problems in this area lead to lots of bodging. I bought a Coupe that had the fan wired on permanently.

[Betared]

That's interesting Neil. It would be interesting to know if you have the 2 separate supplies to fan and switch, and anyone else reading this for that matter. I'm starting to doubt my own sanity now and try and remember the last time I actually heard the cooling fan cutting in!
David.

[HFStuart]

Looking for a cause I found that the feed to the fan is via a single blue wire that goes thru the rad. thermoswitch and the fan to earth.

I think that bit is the key. It sounds like someone has bypassed the fan relay and run the fan power supply straight through the thermoswitch and the motor and then to earth. I hope there's a fuse in there somewhere!

[WestonE]

The OE Blue wire comes from a relay in the box over the exhaust and the blue wire should show 12V with the ignition on. The other side of the connection (Earth) goes to one side of the thermo switch with the other side of the thermos switch going to earth. When the switch connects to earth the fan runs.
So have you got 12V at the blue wire if so with it connected to the fan, earth the other fan connection it should run. Now you know power and fan work so you chase down if it is a switch or earth connection fault. Obviously if you have no power trace it back to the relay and fuse in the box.

Vehicle wiring products sell the terminals and a top quality crimper. I recommend replacing the earth wires whatever the fault found.

Enjoy

Eric   

[Betared]

Finally, a successful result. I had no voltage on the blue wire and wouldn't until the relay was activated. The relay coil needed a feed via the white wire and the thermoswitch to earth.This white wire didn't exist! So I ran a temporary earth from the junction block and by shorting out the thermoswitch had an operating fan!! Now all I need to do is make a tidy run of a new white/black cable and check that the switch operate at a satisfactory temperature.
Thinking back I don't think I was ever in the position where I let the engine idle long enough for it to get so hot that the fan cut in.As I've said at the start of this post it was only because I was setting up the timing and slow running that the engine overheated.
Anyway, alls well that ends well.
David.