Rad fan not working even after new switch.

[airhead]

I can't figure out this issue with the rad fan on my 87 T25 turbodiesel. It has the 2 speed fan and the engine on occasion has gotten more than just a bit hot and bothered meaning I have to run the heaters on full to bring it under control which does work. This generally happens on a hard slog up a mountain hill or on a motorway hill. Last time it happened it was a bit above the red light in the middle of the gauge and there was no sign of the rad fan running. I know it works cause I have joined the terminals and it works on both low and high speed. I changed the switch before as well cause the same thing happened a while back when the engine started to cook going up a hill. I had to pull over. Temporarily I have a switch on the dashboard now to turn it on. It doesn't overheat in traffic. The whole radiator is getting hot so the water is getting to it. Anyone any ideas?

[California Dreamin]

Describing it as you have it sounds as though all it could be is another faulty switch BUT....have you looked at the earth side..
I seem to remember someone mentioning that these are earthed back to the crowns above the fuse box....good place to start as a leaking windscreen corner can cause corrosion in this area.

Martin

[airhead]

What's the best way to test the switch? Just take it out and stick it in boiling water? If it were and earth problem then surely it wouldn't work even with the switch I have on the dash then, no?

[AdrianC]

What's the best way to test the switch? Just take it out and stick it in boiling water? If it were and earth problem then surely it wouldn't work even with the switch I have on the dash then, no?

If t'were an earth problem to the fan motor, then it wouldn't work with the switch jumpered.

Normally, it's set up...
Batt +12v -> Switch -> Fan -> Earth -> Batt -12v

All you do by jumpering the switch is go...
Batt +12v -> -> -> Fan -> Earth -> Batt -12v

Yeh, take the switch out and have a multimeter across it as you boil it. Or just lob another one in. It's barely worth the hassle testing, for the price of 'em.

[California Dreamin]

As Adrian says.....given the implications of this switch not working and the fact that they are known to fail from time to time, £16.00 is a small price to pay for peace of mind.
Don't ignore the earth side though, get this looked at ASAP.
Lastly....fit a good quality switch like Wahler (as supplied by BrickWerks).

Martin

[airhead]

Is a blocked radiator a possibility, cause on the way home from work today the engine started getting hot (I was pushing it on a bit cause I wanted it to get hot) and when I put on the rad fan it didn't cool things down that fast. It did eventually but it made me wonder if the reason it's getting hot could be because of something else.

[AdrianC]

Is a blocked radiator a possibility

Easy 'nuff to check. Get it hot, remove the upper and lower grille, and just feel the surface to make sure it's even all over.

[kevtherev]

coolant flow can be restricted by sludge, in the radiator and/or in the pipework.
It builds up over many years.
It can be restricted by a faulty thermostat, not opening fully.

The fan will cool the coolant very quickly, but if it is not passing through the radiator at the right rate, then the temperature sender will not sense it as quickly as it should...as it's miles away

[airhead]

Waterpump and thermostat are new. The engine itself is well fooked. I think there's a crack in the block cause it was pressurising the coolant system with combustion gases and I've already gone through 2 head gaskets and a known good second hand head so I drained the coolant system and put some of that wondarweld stuff in cause I was damned if I was going to change the head gasket again. That did the trick and it's not pressurising any more. It's still in it though, and you can't run coolant at the same time. Now fair enough the engine may well run hotter running essentially just water with this chemical in it but none of this explains why the rad fan doesn't come on of its own accord.

I cannot afford to change the engine at this point. I'm trying to eek a few miles out of it to do some weekends away in Ireland this summer and over the winter when I'm on a proper wage the engine will be getting changed.

[kevtherev]

I wonder weld if that has bunged up your cooling system

[airhead]

It says it shouldn't, but then all the same to be on the safe side I think I'll have the rad flushed before putting in the new engine whenever I do get one.

[AdrianC]

I wonder weld if that has bunged up your cooling system

Crossed my mind, too - I hate that bodgegoop with a passion.

[kevtherev]

Have you followed any of the advice given
New switch
Clean contacts
Fan checked
Radiator cleaned
Coolant change
Thermostat opening ( new ones fail too)

[airhead]

Yes!

There is a manual switch installed. It still gets hot and the rad fan doesn't bring the temperature down as quickly as I'd like.
The contacts have been cleaned
The fan is fine. It wouldn't work with the switch if it wasn't.
The radiator has not been cleaned, no. That will probably be my next step.
When I'm cleaning the radiator it will get a coolant change.
The thermostat is new and was checked before installing. The old one that came out upon recommendation from someone else was also serviceable upon checking.

[kevtherev]