MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Fan sending unit failure?

The twin cooling fans in front of the radiator aren't coming on when the engine gets real warm. I have power at the fuse box to the black/green wire to the fans. It looks like the sending unit that plugs into the back of the radiator is bad. It may be the original unit, 28 years young. In any case, is it common for this sending unit to go bad? Could there be a grounding problem?
Thanks,
Randy
1977 mgb roadster
randy olson

Hi Randy.

It could be the thermostat, they do fail.
If you carefully bypass it the fans should come on whatever the engine temperature, if they do so you have found the fault.
Using a relay to drive the fans is definitely a good idea in my opinion.

Don
Don

Randy, Looking at the wiring diagram on page 201 of the Haynes MGB manual there is an inline fuse for the fans. It has a white/brown wire on one end and a green wire from the fuse to the cooling fan thermostat. I would check the fuse first. I don'thave a rubber bumper car so I cannot tell you where the fuse is located, it should be in the engine bay. If the fuse is good check for 12 volts at the green wire on the thermostat, ignition on. If ok use a clip lead to jumper the thermostat switch terminals, if the fans run the the thermostat is probably bad assuming the coolant is hot enough to close the thermostat switch contacts. Yes, they do sometimes fail but it doesn't seem to be a common problem.

Clifton
Clifton Gordon

Randy,

I have a 77 mgb. The fuse Clifton is talking about is located underneath the fuse box. You will see three sets of fuses hanging there, one is the white/brown-fuse/green. Check that fuse.

If that does not work I would recheck your relay. The white/brown wire also comes from there to the fuse box.

Ray
Ray 1977 MGB

The fan problem is solved. It was a malfunctioning fuse holder. The in-line fuse was ok, but the spring in the holder wasn't doing its job so there was no connection to the thermostatic switch and fans.
Thanks for all the help.
Randy
randy olson

This thread was discussed between 13/07/2005 and 15/07/2005

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.