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MG MGB Technical - Mechanical Fan AND Electric fan

I've recently aquired a 1977 MGB GT which slowly but surely is getting sorted out. When I bought the car the electric fan was not working and there was a mechanical fan instead. I have fitted a replacement electric fan but am I okay to now disconnect the mechanical fan or did they come with both originally?

Thanks in advance
E Applewhite

You shouldn't have a mechanical fan
Geoff Ev

I think, but could be wrong as it doesn't stick in my memory, that your car originally had an electric fan(?)

not that it matters really

some will say having the back up of a mechanical fan is a good thing but you have to think that it's also cooling when you don't need cooling, when the engine is cold or you've got enough air movement already going through the rad - and the mechanical fan is at its worse when you need it the most, going slowly when at idle

the mechanical fan can take a little engine power and possibly make a little noise, neither usually enough to be of much matter

I'd remove the mechanical fan, in fact my car can originally with a mechanical fan which I've removed and replaced with a thermostatically controlled electric fan

(with no override switch, shock for some, but it's the same as in all cars for the last 30 years)

electric fan will give better warm up for those that actually use their cars during cold weather too
Nigel Atkins

sorry I didn't see Geoff's post when I done mine - I will try to remember '75 on but I bet it doesn't stick
Nigel Atkins

77 and later with the forward-mounted radiator i.e. the large space between the front of the engine and the rad only had the electric fan, as obviously a mechanical fan would be too far away from the rad to effectively pull air through it when the car was stationary.

However a pal has a 78 with a mechanical fan as well, even though the electric fan works, but the interesting thing is that the blades are the wrong angle for the direction of rotation so it is blowing air at the back of the rad while the electric fan is blowing air at the front! Work out which way yours is moving air, and if it is towards the rad then remove it. If away from the rad then it isn't doing any harm, apart from the risk of you getting fingers chopped.

People do get paranoid about rubber bumper cars running too warm, partly due to the narrower angle of the temp gauge perhaps. However until the needle reaches the edge of the red there is nothing to worry about, the whole of the black area is the normal range unlike with modern cars where they seem to stick resolutely at the same position once warm unless something has actually gone wrong. Unless it's steaming or losing cooling it isn't overheating.
Paul Hunt

As Paul noted, an engine-mounted fan on an MGB with the forward-mounted radiator won't do anything for cooling the radiator matrix. However, you could fabricate a shroud that extends back to the fan so that you could get some usefulness out of it! If you choose not to, then remove it as it only absorbs power and thus decreases fuel economy.
Stephen Strange

The background to the change to electric was some work done in the 60s (probably to promote Kenlowe) which showed that the engine fan took a small but appreciable amount of power. Many of us fitted kenlowe electric fans and removed the mechanical fan as a result.
The downside is on the question of redundancy; if the electric fan should fail - you have got to keep moving.The issue was resolved for the V8 with a second fan.
Roger W

But the V8 needs both fans! Lose one and you are in much the same situation as losing the only one on a UK 4-cylinder - BT, DT. Export versions of the 4-cylinder had two as well.

The mechanical fan is a compromise between giving enough cooling at idle, and taking too much power at higher rpms - all wasted if you are moving at any reasonable speed. Even in the UK on a warm day if you are stuck in stop-start traffic the temp gauge will rise inexorably. Mine has got up to the edge of the H zone in the past, but not lost any coolant. There is also a noise issue, later mechanical fans had more blades but they had to revert to the 4-blade for Switzerland and Germany for noise reasons.
Paul Hunt

Just a small point but it isn't actually the radiator that generates the heat - it is the engine, so a mechanical fan on the engine is probably doing a better job of cooling the engine overall even if it is a distance from the rad - better than an electric fan blowing hot air from the rad over the engine, the engine mounted fan will pull cooler air from below as well as the hot air through the rad.

Once the car is moving the electric fan is redundant anyway and can even block cooling air if it is just windmilling.

Chris at Octarine Services

Doesn't matter whether an electric fan is blowing hot air from the rad, or a mechanical fan is pulling it from the rad, the hot air is always going over the engine.

Where the mechanical fan does pull 'cooler' air i.e. not from through the rad it's still going to be air in the engine compartment the vast majority of which will have come through the rad anyway, all of it when under way. Any air moved by the fan that hasn't come through the rad i.e. when stationary is reducing the dissipation of the rad. That's why some cars have shrouds round the mechanical blades, but I don't know whether that was factory or not. Ironically the after-market shrouds that extend across the outer part of the rad as well as round the blades end up blocking the rad more than anything. All they need is a cylinder, with struts for mounting, so that all the air the fan shifts has to have come through the rad, but forced draught when under way can blow through the whole rad.

Whilst electric fans do block some air when they are not powered, they would be blocking even more if stationary and not windmilling.
Paul Hunt

As a question of interest, I would ask which mechanical fan is being used on the RB cars? I have a '77 B which had defective electric fans when I bought it so I replaced them with a single electric fan from a 3 series BMW. It's mounted on the exterior of the rad and is wired as a "puller" fan. I have found however, that on some of our very hot summer days the temp gets quite high.
I was going to add an older "B" mechanical fan, but found that the blades were too long and would actually touch the upper rad hose if installed. I tried both the 4 blade metal fan and the five blade plastic fan. The same negative results.
I fabricated "shroud" to assist with the "distance from fan to rad, but haven't found the right fan yet. I like the idea of "redundancy" also.
JR Ross

is it the fan or is it the cooling system that needs coolant replacing and/or engine block, radiator and heater matrix need crud clearing out and flush/back-flush/flush-again, radiator fins cleaned out, pressure cap checked for correct one and operation of spring and seal or just replace

weak water pump maybe

could also be timing set up or running weak on fuel or brakes binding

or its just normal and not overheating at all

or temp gauge reads high

even if it is running normally regular changes of coolant will help (the coolant elements wear before the anti-freeze elements) and a clean and flush of the cooling system gives added margin especially scraping out the engine block on the drain and flushes as chances are the block has been rarely drained and there's loads of crud their which could lead to 'hotspots'
Nigel Atkins

"which mechanical fan is being used on the RB cars"

As it's a non-standard bodge on 77 and later cars the answer to that is 'anything that fits, and moves air the right way'! You would need a massive shroud to make a mechanical fan of any use in pulling air through the forward-mounted rad, and if you have a non-standard puller fan on the back of the radiator anyway it will be even less effective.

Are you sure your electric puller fan is moving air the right way?

RB cars are said to run warmer on the gauge than CB cars, but I suspect that is as much down to the psychology of the narrow-angle temp gauge on the 77 and later cars as anything. In the UK anyway, I note that all Mk2 and later North American spec cars had a narrow-angle, single-gauge temp gauge.

Everywhere between the upper edge of the C zone and the lower edge of the H zone is 'normal' depending on conditions at the time. Unlike modern cars MGB temp gauges do go up and down according to ambient temperature and how hard they are being driven, or simply stuck in traffic on a hot day. If it's not steaming or losing coolant, it isn't overheating. But if it reaches the edge of the H zone then you need to take the appropriate action. I've seen both mine on the edges of the H zone in the past without any drama.

Other than that as Nigel says there can be many reasons why the engine could be generating more heat than it should, or the cooling system is not getting rid of as much as it should, and a series of temperature measurements through the system may be required.
Paul Hunt

Sorry Paul,
When I said it was a "puller" fan, what I meant was it pulls the air into the front of the rad. I guess most would call it a "pusher" fan.
Us colonials aren't really good with the English language. :-)
JR Ross

Er, that still doesn't tell me whether the fan is on the back of the rad and pulling air through it, or on the front of the rad and pushing air through it :o)

With the forward-mounted rad I would think it much easier to mount it on the back as a puller, even though the original fan would have been on the front and pushing.

The important thing is to confirm air is flowing through the rad from front to back no matter where the fan is, and not the other way.
Paul Hunt

as a totally non-technical person I think the terms and descriptions for fans of blowing, suction, pushing and pulling can be confusing, at first they seem straight forward then a bit more though muddles things, a fan that blows has to first suck the air in - well to my mind

I do follow which is which (now) but still see how it can be confusing

I'm guessing (and as often happens I could be wrong) that JR has a fan fitted in front of the rad, i.e. between the front grille and rad

easiest way to test the fan is going in the right direction is to do a smoke test, very easy if you're a smoker and have a garage otherwise some thick card that you dampen to create more water vapour smoke

(obviously take all safety precautions necessary)

I used a birthday card that kept reigniting itself with the wind after I'd put it out but because my car was outside the wind kept blowing every time I got the card near the car and blowing the smoke away from the rad grille
Nigel Atkins

For the clarification of all the non-colonials: The electrical fan I employ is mounted between the grille and the rad, on the outside of the upper rad saddle. It pulls air into the fan, then pushes it out the backside and into the rad.
It seems to do the job, but I like the redundancy aspect of a mechanical fan.
JR Ross

>>but I like the redundancy aspect of a mechanical fan.<<
sorry but I don't know what you mean by this

if you have a correct electric fan or fans fitted (as two stage or simply running together) then you don't need the engine driven fan which cools when not required and runs slow when it needs to be running fast
Nigel Atkins

"It pulls air into the fan, then pushes it out the backside and into the rad."

That's a 'pusher' then, the word relates to the relationship between fan and radiator. Otherwise as pointed out every fan, taken by itself, is both a puller and a pusher so no point naming it. (Shades of early powered flight and the argument about props mounted in front of or behind the engine ...)
Paul Hunt

This thread was discussed between 19/12/2013 and 20/01/2014

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