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MG MGB Technical - Getting Elec Fans To Come On

This is a question on my 80B LE:

Anyone have experience managing the electric fan sensor plug in the radiator. The fans come on when I jump the two wires at the sensor. Apparently I am not cleaning the contacts enough. Also, the sensor plug wants to pop out now, fortunately it hits the hose when 1/2 out and stops. I've ordered a new rubber seal for the sensor and a retainer clip. I may bypass the sensor in radiator and install a toggle switch on dash for fan instead.

Thoughts?
R.W Anderson

why have a dog and bark yourself - the sensor is supposed to switch the fan(s) on automatically so why turn it into a manual operation, after all you've accepted this system for well over 30 years on 'modern' cars

the fan sensor sounds like it could be faulty or perhaps not fully seated - if you've installed a new fan sensor part recently then allow for poor build quality on such parts

see how you go with another seal and retainer clip and if you've cleaned your contacts well enough add some electrical contact lube to help keep moisture and muck out in future

Nigel Atkins

I have not installed any new parts, I just noticed the other day in traffic my temp was climbing. Pulled in to a shop and they saw that by twisting connection at sensor the fans would come on. Assumption was dirty contacts. I've tried to clean contacts but being recessed makes cleaning difficult. My wrestling with contacts is what may have compromised the rubber grommet that holds the sensor in place. Now it pops out quite easily, but only about half way as it then hits the hose and cannot go out any further.

So if contacts are clean, it may be the sensor itself. I still cannot understand how the rubber grommet holds the sensor in, but when the new one arrives I may understand this better.

But my observations indicate the sensor cannot make a metal to metal contact, fully seated only means the sensor is in the rubber grommet, removing any contact with sensor and metal. I assume this is what is correct.
R.W Anderson

Couple of observations from my experience with a '79. The sensor may not be in coolant if you are low. If the coolant is low the fans may not go on. You may have a leak from the rubber grommet which is losing enough coolant to render the switch inoperable. Finally you can remove the two wires from the switch and connect them together. This will make the fans work all the time. Hope this helps.

Jim
JMcHugh

RW

I don't trust that rubber grommet to hold the sensor in even if it is new. I cut a small piece of wood and taped it to the sensor with electric tape. The end of the wood butts up to the radiator hose clamp so that it can't blow out. If by "recessed contacts" you mean like the female side of a bullet connector, a 0.177 gun barrel brush (pellet gun size) will work to clean it.

Charley
C R Huff

Everyone - thanks for the assistance.

1. Nigel - My daughters had a Basenji, so in that situation they had a dog and had to bark for it. My eldest daughter (who trains rescue dogs)likes your comment.

2. Charely - I am tempted at times to take a gun to either of my MGs, but taking a gun cleaning tool to them may be fine for now.

We'll see what the new grommet and clip does.
R.W Anderson

you could replace the contacts for new but bear in mind some new ones are poorly made so might need tightening when fitting or a year or two later

Jim makes a very good point if the sensor is above the coolant it won't cut in, I was thinking perhaps it needed to be fully seated in to pick up enough heat

Basenji, I had to look that up, these things happen with all this breeding, we have the same problem with the British/European/Russian families
Nigel Atkins

The sensor was originally just a push-fit in a rubber seal, a retaining clip was added later for obvious reasons.

You don't want the electrical parts of the switch contacting the radiator body as the switch extends 12v to the fan motors. Earthing the circuit will blow the (in-line) fuse.

If you are having problems making a good electrical connection to the switch terminals then a new grommet and clip won't help that part of the problem.

Aren't the terminals in the switch male round pins? A rifle barrel brush may help with the wiring connectors, less so with those. A bit of wet and dry wrapped round a probe thin enough to get round the pins should help.
Paul Hunt

new seal and clip is for plug that keeps popping itself out
Nigel Atkins

I used the .177 cleaner but still had a contact problem, so for now I've jumped across the contacts on the wires to have fans come on with ignition. Then I found a piece of steel bar that fit snuggly between sensor and upper hose clamp. All fine for now, while I wait for parts. Just in time of 85-90 temp days ahead.
R.W Anderson

I've finally broke down and ordered the sensor. Hope all this gets me back to normal - or at the least the B, back to normal.
R.W Anderson

if you can check the sensor works before fitting or at least test it fitted to the car whilst stationary at home

I think you can also check it electrically with a meter if you're good at such things

unfortunately many classic owners never or rarely use their cars so want the very cheapest parts they can get so that's what's made and we all suffer for it, doesn't matter to them if the parts work or work well or don't last long as they rarely use their classics but it does matter to those of us that actually use their cars

so don't buy cheap for the sake of cheap, as you've found when these parts let you down it's no fun
Nigel Atkins

A continuity or ohm meter across the pins while the sensor end is submerged in water at 90C+ should show zero ohms, going open-circuit shortly after being removed from the water.
Paul Hunt

This thread was discussed between 15/06/2014 and 25/06/2014

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