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MG MGB GT V8 Factory Originals Technical - Cooling Fan

Hello again,

I have checked the archives but still need more info on installing one big fan instead of two smaller ones.

The one I have in mind is a Davies Craig 16 inch. It flows 2100CFM which is a huge chunk of air (and considerably better than two 8 inch fans).

If anyone has any ideas on how I can creatively stuff this thing in front or behind a lengthened original V8 radiator I would be grateful to here them.

The fan is 424mm x 400mm and 106mm thick. You can place it in front or behind the radiator and reverse the fan and polarity if required. TIA

David Staines

In my research on electric fans I started to get the impression that uni-directional fans are always going to be most efficient and that fans which are capable of working either direction by altering polarity are a compromise. Does your fan really have the same performance in either direction and how does it compare with pullers or pushers of the same size? It might be worth checking.

Marc I can't honestly say that I know about the performance in either direction, just that it's the only decent size fan that I've been able to find so far. I have not yet modified the chrome bumper radiator supports to Rubber bumper so am hoping that I may be able to fit the fan when in the process of fitting the radiator supports/position etc.

David Staines

I fitted a 14 inch fan in front of my rad. Car is a very early (5th one made) rubber bumper GT. Rad was kept in the stock position and the oil cooler panel was trimmed and rolled back, this allowed the fan to sit in front of the rad. A small amount of metal had to be trimmed off the slam panel, and the bonnet release cable's arm had to be shortened. Temp is OK in the occasionally warm UK. Sounds as though a 16 inch fan would be able to suck the car along the road on its own!
David Daw

Thanks David, and yeah it's probably the next best thing to a propeller.
It draws 19 amps (or it says so on the pack) so I guess it works ok.

David Staines

Marc is correct about fan blade design. The aftermarket fan I’m using works as a pusher or puller by not only by reversing the electrical current, but also flipping the blades held to the shaft by a C clip. Other than that, pulling air is more efficient than pushing it. The only reason to push air through a radiator is if there is insufficient room for a puller fan, and there are two obstacles to mounting the fan behind the radiator of an MGB, the water pump pulley is in the way of the fan motor and the anti roll bar is in the way of the fan blades. Keep in mind though; the MGRV8 did use a puller and many conversions have done it.

Here are some numbers to ponder based on quick calculations and crude estimates of fan motor diameter.

First here are the areas of radiator cores.

4” core 72 square inches or 183 square cm
10” core 180 square inches or 457 square cm
14” core 252 square inches or 640 square cm
16” core 288 square inches or 732 square cm

The area of two stock 10” fans is 448 square inches or 1138 cm.
The area of one 14” fan is 444 square inches or 1128 cm.
The area of one 16” fan is 592 square inches or 1504 cm.

Contrary to the numbers, the two stock fans do not out perform one 14-inch fan because the unshrouded blades fling more are outwards than they push through the radiator and even if this wasn’t the case, they are mounted so that they extend beyond the sides of the radiator so some of their potential air flow blows beside the radiator rather than through it.

The ideal electric radiator fan would have a small hub to minimize the dead area in the middle with a remotely located motor.
George Champion

I purchased a fan 16" 3000CFM form Rainbow auto Products in the states for 99.00us. If you want the web address drop me a line


David,you can mount the fan from behind the radiator.Since you haven't made up the new rad support panels,just make some new ones up for positioning thr rad 1-1 1/2 in forward of the standard rubber-bumper location.This puts the radiator close,but not touching the hood release cable bracket.I did this on my car to run a 16in fan from behind and it's been done on a few of my friends' cars.Just pay close attention to radiator cap to hood clearance and you'll be fine.

Thanks guys,

Just to throw a cat amongst the pigeons....I spoke to a local radiator guru here today and he said that an engine driven fan will always be better than an electric one. I wasn't so sure about that, so I was wondering if anyone here would agree/disagree. I have a genuine MGBV8 waterpump but there are threaded holes in the front of the pulley that I could bolt the fan on to.

David Staines

A belt driven fan has to be efficient (never seen any data) to cool the engine at low revs. However, it slows the warm up of the engine from cold and as a fan should not be needed over say 30mph is consuming power when not needed. In Aussie land you may need a fan all the time?


Electric fans move the same volume of air no mater what speed the engine is turning so theoretically would not consume power needlessly at high speeds and still provide a good stream of airflow at idle. I have not seen any electric fan move as much air as an engine driven fan, even at idle. This is just a personal observation based on air felt blowing around with the hood open. Although I have seen a couple of MG V8 conversions with engine driven fans they are uncommon. The slope of the hood places the radiator very low in relation to the water pump so that nearly half the fan is above the radiator core. YMMV
George Champion

"I have not seen any electric fan move as much air as an engine driven fan, even at idle."

The electric fans cut in and out at idle, so must be providing more cooling than is required under those conditions. On one of the midgets the factory had to reduce the 'official' idle speed as that was the only way the engine-driven fan could keep it cool i.e. it was marginal at idle.
Paul Hunt

I have been asking around a couple of MGB V8 conversion places around here and most are saying that there is not enough room for an engine driven fan anyway.

I'm going to persist I think with a modified original V8 radiator and a 16 inch fan. The overall cost is about half that of an aluminium one here and maybe the 16 inch fan will throw enough air through the radiator to keep it cool.

Many thanks for your assistance,

David Staines

<<I have been asking around a couple of MGB V8 conversion places around here and most are saying that there is not enough room for an engine driven fan anyway.>>

Oh? Want to see one?

A/C style engine mounts & radiator in stock location. No hood clearance issues. And it works! No overheating problems at all this past Summer. Of course, I don't live in Australia. You may need additional cooling capacity.


I managed to fit a 12” electric fan behind the radiator of my ’71 when I mounted the radiator farther forward than the stock position on a factory V8 or rubber bumper MGB. Since the body rusted out before the project was finished, I swapped the V8 stuff to a ’77 and left the radiator in the stock position.

Paul Hunt, I wish my fan (fans originally) would cut out, but once it comes on, it stays on because it never cools adequately. Even in the winter the temperature stays high and at idle it nearly reaches the red. In the summer the temperature stays near the red and at idle it enters the red. A traffic jam in the summer guarantees a boil over.

The 14” fan I’m using is rated 2400 CFM so if you can get a 3000 CFM 16” fan and make it fit then that should help. I would suggest getting the fan first and if they let you, take it to the radiator shop to test how air flows through different radiator cores. This seams to be a problem on mine, well that and living in a desert.
George Champion

I used to work in a compagny which sells fans for industrial applications like copiers, heaters, computers, aircos and a wide varity of other machines. One of the most important things is that you take a fan fitted on a (square) mouting plate. Sorry i don't know the correct english word for this plate. You could call it a air guiding plate. This plate with its special curves improves efficiency enormus. If you take a look at the RV8 you see that the fan is also fitted on a plastic plate. The "plates" avoid turbulence as much as possible and therefore give a higher output.
Also in modern cars with their limited air intake because of the grilles, you will find a lot of fan guiding plates.

Peter van de Velde


In your extreme conditions must be a case for - Ally Rad, electric water pump, auxillary tank, vented bonnet, pusher and 2 small pullers and panel between Valance and cross member.

I'm struggling to get to N now, British weather.



Paul, Surrey - that really surprises me, what have you got under the bonnet? My factory V8 will maintain N in temps up to mid 80s.
Paul Hunt

In normal running throughout the year temp is usually well below normal except when stationery when twin fans are well able to keep temp down. Often have a problem though when starting the car when hot cos the fans are running. Would be useful if the starter cut out the fan circuit while starting. Often have to let the fans do their stuff before starting. Anyone have a similar problem?

Simon Pickford
Simon Pickford

Simon - never had a problem (factory V8) starting with the fans on. What problem do you have? If you really want the fans to cut out when cranking change the brown on the relay winding (make sure it is the one on the relay winding and not the one on the contact) for the white/green (unfused) or green/black (fused) which is the accessories position on the ignition switch, this should be disconnected during cranking. It will be powered when the key is in the accessories position i.e. ignition off, which may or may not be an additional benefit.

I'm surprised to see 'well below normal', the stat should maintain it around 'N' except when the heat output exceeds the cooling available.
Paul Hunt


Its only when temp is around freezing that the needle sits to the left of N and a very noticeable swing when the thermostat opens for first time. This normally occurs at my first traffic jam in morning so temp climbs quickly until fans kick in, the rest of year it sits on N.



Thanks for your info on rewiring. The car seems reluctant to start because of ?lack of sufficient spark etc if fans are running. Always OK when they are not.
Recently replaced distributor cap and rotor arm which seems to help a bit.

Not sure what spec the engine is but previous owner spent about £20K on it preparing it for the track but I have converted it back to the road. Its fairly fast - reckon 170 - 180bhp - winds itself off the speedo if really pushed but seem to get fuel starvation problems at that rate!!

S H Pickford

Simon - check the boost connection from the solenoid to the coil. AFAIK all factory V8s have the 6v coil and loom ballast, and the boost connection connects full battery voltage to the coil during cranking. This cancels out the effect of the voltage drop on the battery to about 10v. It is actually quite difficult to measure this as the *average* voltage on the coil +ve during running, as seen on an analogue meter (a digital meter will probably not give a useable reading), is about the same as the boosted voltage during cranking.

If you temporarily connect a ground to the coil -ve i.e. the points-side taking measurements will be easier. With the ignition on you should see about 6v on the coil +ve. During cranking you should see about 10v if the boost is working. If the boost is *not* working you will only see about 4 or 5v.

With a modified car you may have additional problems. A friend of mine took his factory car to a well-known V8 specialist for a power boost. They gave it back with a 12v coil in place of the 6v and an *additional* ballast resistor in circuit - he was only getting about 2v at the coil!
Paul Hunt

Got a hot tip some of you guys might be able to use. Some of the mid '90s Ford Crown Vics such as police cruisers used a real whopper of an electric fan, mounted in the engine fan shroud. I'm pretty sure it could be squeezed into a B with an extended radiator, though it would admittedly be tight. Minimum thickness if you trimmed off everything you could would be around 2" and the diameter is close to 18-1/2". I'm planning on picking up one fron the yard after Christmas, even though I've got a pretty large fan on it now, because after taking measurements I think I can use it.
BTW, on the last engine I did use a crank driven fan, and that is certainly feasible with an extended radiator, which centers the blade quite well.
Jim B

This thread was discussed between 10/12/2001 and 25/12/2001

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