A few weeks ago, with everything switched off and working in the engine bay, out of the corner of my eye, I thought I say a tiny puff of smoke/steam from the front LH side of the engine bay, near the Rad. As the car had just been for a run, I assumed it was some small coolant leak. Looked around and could find nothing un-towards.

A week later in there again, I saw it once more. The Aux Fan relay - the red round one mounted on standoffs (I don't know why the standoffs are there), was arcing and spluttering, all by itself. I quickly disconnected the battery and pulled the relay. It showed signs of overheating.

It was my understanding that the relay has power at all times, so that the fan will run with the ignition off, should the thermal overheat switch activate it. So with that in mind, I replaced the relay expecting the fan to kick in, but nada - zilch - nothing. Then thought the fan had seized and was overloading the relay, so checked the fan with direct 12V and it fine - a bit noisy, but working.

So, one month later, everything is still working fine, no overheating signs from the replacement relay. I opened the "sparking" relay and everything inside looks fine. I expected to at least see some welded/shorted contacts, but nothing. I did not put it back for troubleshooting. Something about sparks in the engine bay that I'm not comfortable with.

On an aside, should the fan not run when the A/C compressor kicks in? I don't think mine does.

I got the relay from Robert Laughton up here in St. Catharines. Robert is a great guy and is a member of this forum. If you need a XJ part, Robert will surely have one for you.

 

If it were my car, I would do some research and thinking. Review the S57 Jaguar schematic.

 

there is a mod to make the aux. fan run when the a/c is turned on. In the V12 engines it constantly runs, so the mod is Jaguar.

did you check Fuse number 5 in the small fusebox next to the coolant tank? it is for the aux. fan circuit.

otherwise the red aux. fan relays always burnout.

 

Jose, A simple feed from the compressor clutch to the relay with a diode or two so the thermal switch and the "a/c on" circuits don't feed into each other should work - I think. Perhaps a more efficient pusher fan to replace the two bladed lawnmower currently there?

Fuse five is fine, sending power to the relay as it should.

That red relay seems to be wired just like a "Bosch" style relay. but I have not tried a Bosch unit. Still do not understand the purpose of the insulated standoffs other than a cooling feature. Glad to hear that my relay meltdown was not unique. Many thanks.

 

On general principles check the contacts inside the plug. They're often quite dirty, causing high resistance....which means extra heat



Was the coolant hot enough to close the thermal switch in the radiator? I think 94ºC is the magic number


Pretty hard finding a fault when no symptom exists. I'd leave the sparking relay as an unsolved mystery....... and keep an eye on things.



No.

As mentioned, many V12 were set up that way, but not the Series III XJ6.

Some early Jaguar diagrams show a tie-in between the compressor and the e-fan for the six cylinder cars but that's not how they were actually built.

A good guy, yes.

Cheers
DD

 

 

that is exactly how the aux fan mod is done, with 1 diode.

The problem is that the aux fan is noisy and running all the time it gets annoying AND in winter you want the opposite, no aux fan. Depending on your climate you might or not do this mod or do a disconnectable mod.

I have it in my '84 but disconnected it, because it seems the radiator thermal switching does its job fine. If I end up in Death Valley, All I have to do is reconnect 1 wire.