Melted fuse

[Alistair C]

Just been trying to pull some blink codes and noticed one of my fuses looked 'funny'.

On closer inspection it's not looking very funny anymore.......

The fuse hasn't burnt out, but the plastic casing has well and truly melted. This is on the radiator fan No1 circuit.

Went through all the others checking the fuse ratings were correct and inspecting for any signs of others going the same way. Found 2 other 30amp fuses with signs of 'warmth'.


Currently I'm thinking:

1) poor quality fuses (they shouldn't melt should they - should be a thermoset plastic - ie burns rather than melts)
2) Poor contacts in the fusebox (leading to high resistance & heat without the excessive current flow)
3) Other electrical issues...............

Any suggestions people?

[Alistair C]

Well, on inspection, the rest of the circuit seems fine with no evidence of heat.

I'm hoping that the heat has been generated by localised high resistance in the fuseboard / fuse connections. I've now changed the fuseboard (courtesy of a nice late model 4cyl 80 and £11), and I'm constantly checking the situation.

Not certain I've found a fix so will search out a decent auto-electrician to see if they can find any fault in the circuit............

fingers crossed.....


EDIT:
Well, for those of you following this exciting story - just been on the phone to a couple of the local auto electricians (one of whom being the local Lucas dealership) and they all suggested I've already done what they'd do as a first port of call.
Their guess would also be poor connections / corroded fuseboard.
Their only other suggestions were if the circuit still overheats the fuse, take the power and control out of the main loom and add in an external circuit to control the fan.......

I did tweek the spade connectors for this circuit so hopefully it should be giving a better connection. Perhaps I should have replaced the connector to be on the safe side.....?

Will take a look at the rest of the circuit in the engine bay too for any evidence of chaffing / shorting / rubbing.

[pastures16]

[QUOTE=Alistair C]Just been trying to pull some blink codes and noticed one of my fuses looked 'funny'.

On closer inspection it's not looking very funny anymore.......

The fuse hasn't burnt out, but the plastic casing has well and truly melted. This is on the radiator fan No1 circuit.

i would look a bit closer towards the fan or the cut in switch for a short

[Beetie]

Jeez i never noticed that when we had the fuse box lid off the other day!
Hope the fusebox sorts it mate, bargain at £11 as well!

[Robatron]

Sorry to drag this old thread up but I was having a nose in the fusebox today when I noticed that the 30amp fuse controlling the high speed fan had well and truely melted.

I also noticed that the fuse for the low speed fan was missing but on closer inspection I realised that it had completely melted!!

The fact these two have both gone would surely point in the direction of dodgy wiring for the fan control unless it is a coincidence that those two fuses would both melt as a result of a dodgy board....

Either way I shall be replacing the fusebox as it looks pretty knackered for both of those slots, but can anybody shed some light on this?

[Nuvo]

Are you saying that fuse numbers 5 and 20 have gone but 15 is intact?
The attached wiring diagram should be enough to troubleshoot the fault.
Hmm. S15 isn't shown in any of my drawings unless I've over looked it.

I hope that the high speed relay (J101) and the after run conrol unit (J138) have survived this catastrophe.


Cheers,
Rob.

[Robatron]

It would appear that fuse 15 is intact, perhaps this suggests a dodgy fuseboard and they were the two casualties by coincidence?

[Robatron]

Interestingly though, I have never heard the high speed fan since I bought the car, nor have I heard the after-run fan on....

[Nuvo]

It would appear that fuse 15 is intact, perhaps this suggests a dodgy fuseboard and they were the two casualties by coincidence?

Fuse 15 is for the fan switch, it isn't fused for the diagram I posted, but then if it is still intact then the brown/green wire to the high speed relay (pos #2) should be okay (A87K). I would check for continuity all the same.

[dan_b]

@Rob - I know the high speed fan used to work; it takes quite a lot of effort to get it to come on, I only remember triggering it on a couple of occasions, all when it was extremely warm, after I'd driven it in a rather spirited fashion and of course the aircon was on at full blat. I think probably even then the full-speed fan came on mainly to assist the aircon rather than the engine temp.

Does sound a bit suspicious with the fuse box and the after-run pump though.

[Alistair C]

My wiring had been butchered by a previous owner. Ill fitting spade terminals had been crimped onto wires which had been cut too short. And a complete PITA to replace due to location. Eventually found the correct connector and associated repair wiring strips and had them soldered in.

Still not sure why the fusebox took the hit though. Wiring looked intact and connectors appeared secure.

90% of the wiring on the back of the fuseboard are in multi-terminal blocks. And these all looked fine on mine. Though one of the melted fuses was on its own individual spade connector - and this one had heated so much that it had melted the fuseboard all round and through to the wiring side.

No real answers for you (apart from to look out for butchery) but the new board and replacement connectors seem to have called a halt to further problems.

Mine also had A/C.

[pastures16]

My wiring had been butchered by a previous owner.

no you are wrong there sir it wasnt bodged by the previous owner lets get that right

[Alistair C]

no you are wrong there sir it wasnt bodged by the previous owner lets get that right

I did say by a previous owner, not the previous owner ......

[s2driveruk]

when my fan shorted out it melted the fusebox....the current draw for the fan is mahoosive, something like 50amps. Disconnect the battery and have a good look about if i were you

[Alistair C]

Its also a mammoth startup draw especially if the bearings are getting tired.

I know later cars had a separate fuse on the earth return - there is a article on one of the forums suggesting earlier cars were retro fitted with the later parts as the original design was not protected well against overload.....