Allegro Club International

[Colin T]

Following on from my previous thread about the radiator fan temperature switch, I bridged the wiring that goes onto the switch to make the fan run constantly.

After a return trip totalling 1 hour 40ish or so, I noticed the temperature was a bit higher than normal when in town, with stopping at lights and stopping to drop people off, this with the fan supposedly running constantly too.

I did a static test, just switched the ignition on and no fan. I undid my bridging and shorted the wiring with a screwdriver to see if my taped -up short had failed, and the fan ran very slowly, it spun a few times, then twitched, then just made noises, and then nothing (this was without a constant short, this was several attempts at shorting, with less fan action each time).

I saw that the connector that plugs onto the thermostatic switch has melted a bit inside, not sure if this means anything. I guess it gets hot as the pins that go in to it are part of a unit that sits in very hot water.

The connector and all fan related wiring appears to work perfectly well in various tests I have done.

I tried running the fan directly off the battery but it does absolutely nothing. I dismantled it and it smelt of burning.


Some of the windings of wire look like they had a coating that had melted slightly.


Can anyone tell me if anything is obviously amiss with my fan? Are the brushes OK? I honestly don't know what these look like when knackered. I am having a spare fan sent to me but any help with finding the fault with my original fan is greatly appreciated!

Thankfully my car hasn't overheated despite switch and fan failure, due to checking everything thoroughly very often!
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Hell has frozen over...... the car formally known as 'Heap' is back on the road!

[Richard Howe]

You didn't wire this off an unfused supply did you? Sounds like it's been drawing too much current if it's melted the wiring...
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...that's why Allegro will look as good 5 years from now as it does today.

[Colin T]

No - I just bridged/shorted the connector that goes onto the rad fan switch with a piece of metal. That was all that was need to make the fan run constantly, the power came as normal down the proper wiring through the ignition switch.
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Hell has frozen over...... the car formally known as 'Heap' is back on the road!

[Colin T]

Can anyone see anything wrong in the pictures?

Also, quick question - should the fan 'push' air through the radiator and grille to outside the car, or should it 'suck' air from outside the car into the engine bay?

Many thanks, Colin.
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Hell has frozen over...... the car formally known as 'Heap' is back on the road!

[Richard Howe]

Logically it should suck, but I don't have Gonzo to hand so I can't confirm whether BL followed logic.

An important consideration here is that the fan should only be needed in slow moving traffic; once a car reaches 30mph or so the fan should be rendered useless by normal airflow, and that's a standard design goal.
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...that's why Allegro will look as good 5 years from now as it does today.

[Colin T]

I have a replacement (second hand) fan fitted now, sent courtesy of my personal Spares Controller (AKA my Dad). It runs fine with the ignition switched on, as the connector to the fan switch is bridged.

The fans have an arrow on the moulding, showing that they spin clockwise when viewed from behind the car. I think this means it will 'suck' air through the radiator, rather than blowing air through it (my fan has only come on in past after having been driving slowing in traffic or whilst stationary).

The replacement fan was very clean internally, pretty much spotless, and so had none of the black/dark brown thin sticky layer that was covering the old fan in the pictures above. Also, the wires in the fourth picture were all orange. I assume the black/dark brown sticky reside had melted from those wires in the fourth picture.

Question remains: what went wrong? why did my apparently healthy fan die after less than two hours of use (with about 45-50 minutes constant use at the most)? It looks like it overheated and burnt itself out, but I don't know what is actually wrong and why it won't work now. I did notice that the connector to the fan from the wiring harness was loose, could this have caused the problem?

Any help suggesting what happened is greatly appreciated, so hopefully I can avoid this happening again! Especially as I need to drive to Norfolk and back next weekend.
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Hell has frozen over...... the car formally known as 'Heap' is back on the road!

[Laurence]

Hi Colin,

Not having stripped a fan motor down, I don't know whether it has ball bearings or bushes, but, judging from the condition of the armature shaft it probably has bushes which are worn excessively.

If that's the case, the motor would have overheated & 'burnt-out' (because it was being overloaded).

The brushes appear to be worn excessively ie they're too short & the brush tip which bears upon the commutator appears to be worn at an angle rather than square.

The brushes wear pattern on the commutator looks uneven ie the wear band is wider than the thickness of the brushes, which makes me think there is too much 'endfloat' of the armature.


Check the internal condition of the armature bushes in the end-caps for scoring/uneven wear.


If you re-assemble the motor, test for excess lift on the armature shaft by wiggling it side-to-side, & then test for endfloat by pushing the armature toward the motor & then pulling it away from the motor. there should be minimal 'play' during both these tests.

Spin the armature in the motor by flicking it around with your fingers, check for any signs of rough running/vibration.

Could this duff fan motor be the cause of your overheating/head-gasket failure you wrote about recently?

[Colin T]

Many many thanks for your reply Laurence - it is very helpful and has pointed out the problem.

The armature has a fair bit of movement, 2mm or so of end-float, and there is wear when I wiggle it side-to-side. The replacement (2nd hand) fan has about 1mm of end-float, and less movement side-to-side, but it is noticeable. the brushes on the old fan are worn at a noticeable angle.There doesn't appear to be any roughness when I spin the blades though.

I can't examine the armature bushes as I cannot remove the fan blades (grub screw is stuck) but if I wiggle the end plate of the fan (with the fan dismantled), the is a massively huge amount of movement, which is very obviously a problem! I now need to look at this movement on the replacement fan and see how bad it is.

Just wondering - when the fan overheated and 'burnt out', what actually stops it working? I guess some of the electrical parts get frazzled in some way and conk out?

I haven't had any over heating or head gasket problems recently - January last year the car over heated and warped the cylinder head, but this was because the connector to the rad fan switch was unplugged by me when I inserted some blanking infront of the radiator and I only remembered to plug it in when the needle was going towards Red when sat in a long traffic jam! Won't be doing that again.

Thanks again, Colin
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Hell has frozen over...... the car formally known as 'Heap' is back on the road!

[Colin T]