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MG MGB Technical - COOLING FANS

My 79 MGB overheated last week while in crawling traffic. Open highway is no problem. I did notice the cooling fans did NOT operate. Further probing, I discovered if I remove the hot wire from the radiator mounted sensor and touch it to the terminal on the other side the fans work.

My assumtion is the sensor is no good. If this is indeed the case, what procedure is required to replace this sensor?

Any thoughts???

Thanx in advance

Cheers

Gary :>{D
79 MGB
gary hansen

I believe that the switch on yours simply unscrews with a spanner on the hexagon flats (after unplugging the wires) and swaps for a new one. If you do this with a cold engine fairly quickly, you will only lose a trickle of water, just top back up.

If it is the type that is just pushed into a rubber seal it is more tricky, as it pulls out (yes: nothing whatsoever holds it in, just faith) then you fish out the seal, replace the seal and push in the new one. You will lose quite a bit of water, position a container to catch it. Then find some way of securing the sensor from just blowing out, mine has copper wire passing round the header tank and keeping the switch in place.

You can wire a heavy duty switch across the sensor wires as well as the sensor, then turn the fan on manually if the sensor fails (The new cheap parts often do I'm afraid)
Martin Layton

The sensor switch is a fairly easy replacement. When you order the switch order a new heavy duty rubber grommet replacement to hold the switch in place. Best to drain a little coolant from the radiator via the bottom hose but if you dont mind being quick and a little sloppy you can pull the switch and grommet quickly and insert the new with some spillage. For me, I prefer to keep the engine compartment tidy and drain a small quanity then top off. The replacement switches are fairy inexpensive order two so you have one on hand as a backup. Martin is absolutely correct in saying that a way to secure the switch in position is a good idea. Myself I made a a bracket out of a piece of stainless steel bent to the contours of the top of the radiator and cut to accomdate the switch, works like a charm, never lost a switch yet.
JCH Hibbard

Went to order the part and discovered there is a difference between the 79 & 80 radiators. As I am NOT the original owner of the car, I think a prevoius owner replaced the radiator with a 1980 unit. Mine has a retaining clip which appears to hold the sensor in place. There is a difference in part nbr as well as price. I did order the sensor,bushing and clip. Will report back when task is complete.


cheers
Gary :>{D
79 mgb
ghansen

Ok replaced the cooling fan sensor the other day and all went well. This went much easier than expected, pleased to say.

I understand the radiators for the 1977 - 1980 MGB's have been upgraded to the 1980 style configuration hence using the 1980 cooling fan sensor. This is an item all need to check before ordering a replacement sensor.

cheers

Gary :>{D
79 MGB
gnhansen


Hi Gary,

How were the fan switches different? My '80 needs a new one. Were the two switches interchangeable between the two different radiators?

Thanks,
Dave
David Plantz

David: As I looked this item up in the Moss parts catalog, I noticed a difference in the physical configuration of the sensor. Further looking down the parts list, it indicated there is a difference between the 79 and 80 radiator. That lead me to call Moss. I was informed the radiator replacements have been superceded to the 1980 configuration. It is truly a simple upgrade with no modification required. the wires hook up the same as ever, but the sensor itself is a "round plug" confiuration with the two terminals on the back.

To answer your question, as I do not have the 79 radiator, the picture in the Moss catalog is different for the 79 sensor than the 80 sensor which is what my car has. The 79 sensor appeared to have an oval shape at the terminal end side of the sensor and it appeared slightly differnt in length.

Again, I am not the original owner of the car and the radiator had to been changed at some time in its life. So the radiator is the 1980 configuration.


cheers

Gary :>{D

79 MGB
gnhansen

This thread was discussed between 25/08/2008 and 04/09/2008

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