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MG MGB Technical - electric fan

can anyone tell me if i can hook up a larger electric fan from the small one fitted to the front of the rad on my 78 b gt and remove the one on the crank or will i have to get a electric fan with a tempratur senser thank you .. chris
c mudie

You should not have a fan on the water pump pulley, the sensor for the electric fan is in the rad header tank, held in with a rubber grommet. Perhaps a PO has fitted a mechanical fan because of a problem with the electric one, mine used to blow the sensor out of the grommett untill I secured it in.
c cummins

oh right??? must have been put on by a po then. so they hade an electric fan as standard then not on the water pump? will have to have a look more closly tomo thank you chris
c mudie

will take a pic tomo and post it on see what anyone thinks
chris
c mudie

Chris
If it's the original electric fan on your car it's quite capable of coping with the job by itself in any temperatures I've seen in the Uk in last 15years [assuming the cooling system is in good working order]
Ron
R. Algie

Chris it's worth checking the engine number to see if it matches the year of the car. Use this site

http://www.zeke.ne.jp/~glitter/main/html/mgb/mgbdata/MGBdata2.html

If a PO swapped the engine to an earlier one he may have left the fan on.
I would be surprised if the electric fan ever cut in with a mechanical fitted.
You will have to check the electric fan is working. This cold weather may make it difficult by just running the engine at tickover. You may have to take the sensor out and and test it in a kettle, should cut in at 90C.
c cummins

chected the engine numbers out and the log book and the website and they all match, took the fan off the water pump but had to refit it as the bolts was too long without the fan they stoped the pump from turning,the electric fan works fine and the system is nice and clean (changed the water and anti freez) this is a strange one as its also got a vinal roof and sunroof lol will keep digging to see what i can find
chris
c mudie

A friend has a 79 with working electric fan which has also had a mechanical fan fitted. When he got the car it didn't have overheating i.e. running too hot problems, but it did suffer from coolant loss at switch off, which was due to the 15lb radiator cap only holding about 5lb of pressure! Not only that, but the mechanical fan was of the wrong design and was blowing air towards the radiator, i.e. opposing the electric fan! They don't call them 'dumb previous owners' (DPO) for nothing.

Nothing strange about vinyl roof and sunroof, they were both popular period accessories/mods, both were big business in the aftermarket.
PaulH Solihull

Not only DPOs. Over 40 years ago, I drove my first MGB to Switzerland and back, It constantly overheated and I had to resort to running the heater fan to keep it going. I suspected the timing and took it for a "Crypton tune up" when I got back, the mechanic told me the fan was on the wrong way round. I was the second owner and it had either come from Abingdon like that, or been removed and put back wrong at a garage.
Apart from that, is it possible for the electric fan to be running the wrong way.
c cummins

Hayden 14 inch pusher with thermo sensor " on" ( variable or preset) relay retrofit is easily done in about 2 hour complete

vem myers

PaulH is closest to the mark on fans "pushing" instead of "pulling".
You cannot correct the direction of airflow merely by turning the fan unit radially through 180° - this does not affect the pitch direction of the blades, just the efficiency. If your mechanical fan is "pushing" air forwards into the rad. then it is the WRONG fan.
Do I remember correctly; did transverse engined Minis, 1100s etc. have fans that "pushed" air through the rad? (I could be wrong) If they did, then perhaps Mr Cummins B from 40 years ago might have had one of these fitted by mistake.
As for when it was fitted - bear in mind that those were "Red Robbo" days for the British Motor Industry and goodness knows what bloody British Leyland were playing at then!!!!!!!!!!!
J Barnacott

I've nothing to add about fans, but vem, what's with the random photos?
Rob Edwards

"Do I remember correctly; did transverse engined Minis, 1100s etc. have fans that "pushed" air through the rad? "

They did indeed, because it was a side-mounted rad so that is the natural way for ram air to blow it, which is the thing that determines fan blowing direction. Even the illustrious (or not) Edd China didn't seem to know that when 'restoring' a Mini Moke.

Which way the engine it was originally attached to also determines fan blowing direction, many Japanese engine rotate the opposite way to BL at least, for example.

Having a fan on the wrong way round does have an effect on efficiency, but it is marginal. I ran my roadster like that for nearly 20 years before I discovered it and never had an overheating problem. Mine was like that because it had a short-nose water pump without the fan spacer. I obtained and fitted a spacer to correct the fan, but can't say I have noticed any difference. I *did* notice the difference by fitting the foam strip to block the gap between the top of the rad and it's mounting panel, after a similar number of years without.

And yes it is very easy for an electric fan to be running the wrong way, simply by reversing the wires on a motor with a permanent magnet stator, which most are. That has a huge effect on the performance of the heater fan (with different coloured wires), by the way.
PaulH Solihull

So to get back to Chris, with his OP should check that the electric fan is pushing air. With a mechanical fan fitted it probably never cuts in.
As to being told 40 years ago that the fan was on the wrong way, and knowing then even less about MGBs then, than I do now, I took his word as gospel. I know I turned the fan round, perhaps becoming a DPO (dumb present owner), no, not perhaps, I know I've done plenty of dumb things.
That's what makes this forum so helpful, not only the expertise, but also the owners who have messed it up and are willing to share those disasters.
c cummins

Because the radiator is so far forwards of the engine on a car with factory electric fan compared to mechanical, an additional mechanical fan will have almost no effect, even blowing the wrong way a my pals does! He decided to leave it how it was as it is doing no harm, and we may have to fiddle about getting alternative pulley bolts if we removed it - even though that should only mean shortening them.
PaulH Solihull

This thread was discussed between 01/12/2011 and 12/12/2011

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