Four Blade Fan

[Colin Morgan]

There will be a small contribution to forward moment from the air driven backwards by the fan. However, most of the energy is wasted in yet more heat...

Colin

[AustinWood]

I rather suspect that the Austin Seven fan does more stirring than sucking.
It needs to be close to the radiator and would benefit from a cowl to allow it to generate a low pressure region behind the rad.
Neither really feasible on the Austin.
For much of the year I run with no fan belt. Only a slight problem if in stationary traffic. If there's hot sunny weather I refit it if I remember.
My fabric saloon has solid radiator sides which must impede the flow. Usually the hot air comes up around the gearbox into the car. I cover that up in summer as it overheats the occupants. Nice in winter though so long as not exceeding 45mph, when the cold air takes over.

[Steve Jones]

I recall a friend's Trials Seven that continually overheated. He tried various things without success until one cold morning, trying to warm my hands on his radiator, I realised that air was being blown through the radiator, not sucked through it. Coil engine, magneto fan blade!! For that day we simply removed the fan belt and the overheating stopped. Fan blade replaced with the correct one and permanent end of problem. The fan does do something. Hold a handkerchief in front of the radiator with the engine ticking over and you'll get an idea of how much.

Steve

[Colin Morgan]

As you probably know, there is a big difference in heat transfer between natural and forced convection - perhaps a factor of 5 - so having a fan running when the car is stationary should help cooling significantly. However, once the car is moving, the air will be forced through the radiator anyway so the benefit is reduced - hence not much difference at 40mph - perhaps surprising there is any?

Not sure it is practicable, but a single twist in the belt and the fan would run the other way - mag to coil!

Colin

[Reckless Rat]

I have had a 4 blade fan on the RP for a number of years and it has made an appreciable difference, particularly when climbing. The car has never boiled even after tackling hills like Mont Ventoux and the Col de la Bonnette. I tend to leave the drive belt on the slack side to reduce the forces acting on the spindle shaft, but with enough tension to keep everything turning. I don't know whether the position of the fan on the later cars is different to the RP but there's no way you can remove even a 2 blade fan on the RP without removing the radiator. In the case of the original post, is the correct fan pulley fitted? The fan should be as close to the radiator as possible.

It's worth noting that in winter, warm up times are greater with the 4 blade fan.

[John Mason]

I agree with Recker's about fan belt tightness and tension after all you are only driving the fan no Dynamo or alternator to worry about belt slip.

John Mason

[Colin Morgan]

I think the fan pulley is as standard on this car. There is a gap of 1/2" between the top of the two small bolts holding the fan and radiator fins. This was enough to loosen the bolts. The fan could then be pulled off and rotated about its long axis to remove it. (As the four blade fan could not be rotated because of its shape, it wouldn't go on the same way, and the radiator had to be moved away to fit it.)

The belt seems almost slack - doesn't seem to need to be tight like a V-belt - has driven the 4-blade fan okay, so far.

Colin

PS When I arrived back today I left the engine running, then held my hand (with care) in the air stream coming from the fan. The water in the top tank was at about 90 degrees, but the air the fan had just drawn through the radiator felt relatively cool and the temperature under the bonnet seemed lower than usual.