Radiator fan motor

[CJH]

Ah, just in time there Ralph, thank you. I was just about to post that my early fuse box doesn't have a rad fan relay in the relay plate.

Back out with my torch.

E D I T: A job for another night after all. The glove box has to come out to get the fusebox out of the way. Not in the mood tonight.

[tandemsandy]

Mmmmmm interesting, and well timed!
I'm replacing the radiator so have got the rad fan & shroud in the garage. Shroud cleaned & repainted, but having read this, and especially the comments about motors rarely failing, I've just made a discovery!

9 months ago I'd found the low speed not working. The paperclip method showed the fan ran when closing the high speed side of the thermoswitch, but nothing on the low speed. I concluded the low speed windings/resistor in the motor were knackered, so to be safe I swapped the wiring such that the low speed contact on the thermoswitch ran the motor on high. It worked perfectly well, but did sound like a hovercraft!
Anyhow, having read this I decided to check the fan again. Wired the battery direct to the high speed contacts on the fan - fan runs. Wired direct to low speed side - blimey, that works too!!!

So my previous diagnosis was wrong, the motor is ok on both speeds, something else was stopping current in the low speed circuit between the switch and the motor. Will investigate further when its not dark & chucking it down, but am I right in thinking the low speed is wired direct from thermoswitch to fan motor? There's only a relay on the high speed circuit? So it must be the disconnect plug on the motor that was breaking the circuit?

Club 80-90 strikes gold again

Rob & Sandy

[CJH]

Well what do you know - I DO have a two-speed fan after all

The relay (in the bracket above the earth crown as described by Covkid) was faulty - no action at all when power was supplied across 85/86. I popped in a spare relay and the higher speed worked. For a moment. The 8A fuse blew immediately. I replaced it with 16A and it seems ok. Any idea what the correct fuse rating is? The various sources of info on the early fuse box don't seem to match up to what I've got. My meter only goes up to 10A, so if it blew the 8A fuse it may well exceed what my meter can cope with.

[CJH]

Oh dear - I've just checked the handbook (why didn't I think of that before?), and it says the radiator fan should indeed be 8A. So is my fan on the way out if it's blowing 8A fuses?

[CovKid]

Therein lies the problem and it can be just as bad if not worse with blower motors which is why I don't recommend (as some do) drilling holes in the front to spray in WD40 and the like. Its pointless. Whilst well-meaning, the person who originally posted that (on the Samba?) rather overlooked the problem . The surge from old fan and blower motors on start-up can be excessive, Yes it might free a stuck bearing, but most of these motors are around 30 years old and long overdue for replacement already. Often the fuse rating has to be increased proportionally and you'll eventually get hot wires and all sorts. All these motors (in my view) should be on relays too, if not already.

[CJH]

Ah yes, the start-up surge. I guess testing the high-speed fan in isolation was a bit unfair, since it's designed to normally come on when the fan is already spinning, thanks to the low-speed switch, so the start-up surge would be less. The fuse has never blown with the low speed fan.

Nevertheless, given that the 2.5mm2 wiring can cope with more than 16A, particularly if it's only a momentary surge, I think I'll leave the 16A fuse in place. I want to be sure that the circuit will work when required. Perhaps I'll get my meter out after all to try and see what's going on.

[CJH]

I've tried to measure the surge and steady state currents. My meter doesn't have a 'peak' function, so I found an unwilling helper to watch my meter and tell me the biggest number he saw while I made the connections at the thermoswitch plug. I think observing the peak this way will be wildly inaccurate since it will depend on the response/update time of my meter, but nevertheless the results are fairly consistent over several measurements, which I've averaged below.

- Turning on just the low speed fan, I got an initial peak current of 9.0A, settling quickly to 5.7A

- Turning on the high speed fan while the low speed fan is running, I got an initial peak of 13.5A, settling to 10.6A

- Turning on just the high speed fan from a stand still, I got an initial peak of 22.5A, settling to 10.6A again.

So yes, as expected that initial surge when the fan spins up to high speed from a standing start is greater than when it's already running at the low speed. This shouldn't be a problem in normal running, since the low speed fan should always be running before the high speed cuts in.

But the steady current at the high speed setting seems too much for an 8A fuse to sustain. So I'm going to leave the 16A fuse in there.

Maybe when I have the whole lot out to replace the radiator I'll see what can be done to lubricate the motor and fan.

[AdrianC]

- Turning on just the high speed fan from a stand still, I got an initial peak of 22.5A, settling to 10.6A again.

So yes, as expected that initial surge when the fan spins up to high speed from a standing start is greater than when it's already running at the low speed. This shouldn't be a problem in normal running, since the low speed fan should always be running before the high speed cuts in.

It's unlikely, but it's not impossible.

If you've had the van good and hot, then stopped for fuel or a pee or scenery, then the fan will continue to run - but it'll only cool the coolant in the rad, because it's not being circulated by the waterpump (JXs have an auxiliary electric pump, I think, so this might only apply to WBXs). The rad cools down, the fan switches off. Meanwhile, heatsoak in the block continues to raise the temperature of the coolant. You switch back on, and VERY hot coolant goes from block to rad, and hits the thermoswitch.

Either way, 22A is a big old wodge of current.

[CJH]

Either way, 22A is a big old wodge of current.

It is - but it's only for a moment. Not long enough to do any damage to 2.5mm2 cable. And I've just realised - it's quite an impressive reading for an ammeter that's fused at 10A. Obviously not a quick blow fuse.

[CJH]

I picked up a fog light switch from Bustypes at the weekend, with a view to using it as a chicken switch - it seems ideal, since it's a two position switch so it'll have to go through the low speed setting to get to the high speed setting and should therefore minimise the start up surge.

The execution of the artwork is at the 'proof of concept' stage - what do you think?!

[CovKid]

Maybe a poo icon? After all, its there for when you're in it.