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MG MGB Technical - Electric fan problem

i have a 79 MGB that has been in storage for a while. i have it running ok bu the fan is not coming on. how can i test the fan and/or switch?
John

This happened to me a few times with various MGs. There is/should be a sensor on top of the rad wired to the fan. When things get hot ( about half-way on the gauge ) the fan will come on. However these things were always packing-in on me. I have had 3 MGs and always use them as daily drivers , and on all of them they have had electric fans and the sensor always failed at some point. I do most of my driving in traffic ( london now , and previously Dublin , 2 of the most conjested places I have been!) and found that for simple peace of mind an override switch is the best thing to do. I have got a switch installed under the dash which turns the fan on or off when I hit a jam ( i.e outside my front door!) , so basically when the gauge goes up to around half I just knock it on. The sensor is still connected and put the fan on aswell. Having the switch just gives me more confidence when in traffic. Dead easy to put in ourself or a garage will charge about 25quid to do it.
daryl

John,
Test the fans by removing the plug-in connector at the radiator next to the top hose and use a jumper wire to connect the two female pins in the connector together. If fans run switch is bad or radiator doesn't have enough coolant in it. If they don't run, check to see if you have voltage at the connector with a meter.

Mike
'79B
Mike Janacek

i think i have found part of the problem.....the fan is pooched. i jumped the wires at the swithch and still no fan. i then put a meter on the fan wires and there were 24V????? i took the fan out (that aint easy) and took the fan apart - the brushes are so worn they are not touching the armature. now can i find the brushes? now i'll need to test the switch- help? what about that stupid plug?
John

Gosh do those OE fans stink. They also apparently consume enough power to light up Bayonne, NJ on startup -- I keep blowing fuses when they go on and I've gotta wire up separate circuits for each I guess. Not only that, the piece de resistance is that they are just grossly, grossly ineffective. When they're on, the air just seems to bounce off the rad and back out of the grille! What kind of brainless amoeba designed 'em, and/or spec'd them for our cars?
Sam

I just added an aftermarket 10 " fan directly to my radiator , pusher style - it works great although it's a bit noisy , just drive faster and you'll not hear it ! .

To make more efficient and much quieter , take your duck bill pliers and remove most of the strips added to keep stupid people from jambing fingers in it - you'll be amazed at how quiet and efficient it suddently gets but don't let OSHA see it :-)

-Nate
NSH

If the standard fans blow fuses when they start up you either have the wrong fuse or something is drawing more current than it should.
Paul Hunt

I'm not sure if I have the same problem , that is worn brushes, but my fans need a little tweaking, too. One fan seems to work fine. The other doesn't move unless I push it to start, then it seems to run, but at a slightly lower RPM. Any ideas?
PS: The car has been sitting for 5 months and it's just coming out for the summer. It hasn't been overheating and seems to run fine.
Randy
1977 MGB
randy olson

i have this unbelieveable 72 year old neighbour, he took my fan motor and rebuilt it! they are a real heavy unit! he had to make brushes and a new rear bushing. how cool is that? they are pretty simple so if you take it apart you will be able to see if the brushes are OK or not.
John

I think I'll pull out the fan and take it apart to see if the brushes are ok. The fan doesn't turn at all now, even if I give it a shove. Plus, it was make a little noise last night.
Cheers,
Randy
1977 MGB
randy olson

Randy - yours sounds like brushes.
Paul Hunt

Well, I looked at the brushes and they seem ok. But there is a blackish glaze on the comutator (?) that I think is suspect. I'll clean it off and then hook the motor to the battery charger and run some 12v power through it to see if it runs. If it does - problem solved, maybe.
Thoughts?
Randy
randy olson

if its not your brushes it may be the rear bushing is binding. or perhaps the bearing????? are the magnets on the inside marked?
John

The magnets aren't marked and the bearing seems fine since the spindle spins freely. I have the motor on the bench and am trying to test it now with the battery charger but nothing's happening...hmmm.
Randy
randy olson

Will your charger supply enough current? Charger outputs often aren't a steady 12v but simply rectified AC, sometimes only half-wave. Without a battery across the output the voltage is probably not what you expect. Then again, maybe its the motor. Put a test-lamp in series with the charger and motor. If it doesn't light the motor is open circuit. If it does current is flowing through the motor but not enough to spin it for some reason. Putting it on a battery is a better check of the motor.
Paul Hunt

Paul,
The test light lit up quite bright, so there's not an open circuit in the motor. Since I don't think I can hook up directly to the car's battery, and I don't know what other battery to use, I guess I'll eat lunch then put the fan motor back in the car and try it out.
Thanks and I'll let you know what happens. If there is another battery I could try while the motor is on the bench please let me know.
Cheers,
Randy
randy olson

Well, I put the motor back in and mouted the blade, took a short trip, then let the engine idle until the fans came on. They both came on! But the bad one seems a little slower, then it made a little noise...bearing!? I spun the blades around after the engine was shut off, and the bad good fan seemed a little easier to spin. The bad one slowed quickly. Is there a way to lube the bearing? Can it be replaced? Next move is to remove the motor again and take a look.
Randy
randy olson

I believe the problem is solved. There was a missing thrust washer inside the motor. I was looking at the exploded diagram in Haynes and noticed the washer was shown, but there wasn't one in the motor. So I found one that fit and put it in...bingo. The fan came on and runs smoothly; no wobble, speed is the same as the other one, quiet. And it's nice and clean.
Thanks for all the help.
Randy Olson
1977 MGB Tahiti Blue (with bright yellow fans that turn!)
randy olson

This thread was discussed between 22/05/2002 and 25/05/2002

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