4 blade or 2 blade fan

[Russell Fredy]

I am interested in any feedback on performance issues anyone may have had with either a 4 blade or a 2 blade fan on an AA. I think the 4 blade was the original for a truck. However I have also heard that a 4 blade fan will take away some power. On the other hand would a 2 blade fan cool the truck enough under working conditions?
Russell Fredy

[Chris Haynes]

I am interested in any feedback on performance issues anyone may have had with either a 4 blade or a 2 blade fan on an AA. I think the 4 blade was the original for a truck. However I have also heard that a 4 blade fan will take away some power. On the other hand would a 2 blade fan cool the truck enough under working conditions?
Russell Fredy

Think again. All A's and AA's had the two blade fan. The four blade fan was a later replacement part.
I am installing an thermostatically controlled electric fan on my AA.

[Rosenkranswa]

The A's and AA's originally came with the 2-bladed fan, I believe the 4-bladed were from the V-8 era (not the plastic ones of course). I have a 2-bladed on my AA, and a 4 on my A pickup. I can't see that either does a better job than the other. The 2-bladed has an airfoil shape to the blades which is supposed to move more air than the flat blades of the 4. I have noticed that the smaller '28/'29 radiator probably doesn't provide enough cooling area on an AA as mine will overheat on a moderate hill. Probably why they went to the additional row of tubes on the '30/'31.

One possible consideration is that the MARC Touring Class judging used to require a standard 2-blade fan as part of the entry criteria, although I don't see that listed in the most recent Model A News.

[Neil Wilson]

Years ago there was an article in MARC or MAFCA regarding the 2 and 4 blade fans. The study found that the 2 blade was either equal or better than the four blade.

If you have a 2 blade fan, then the water pump (with fan) can be removed by tilting the radiator foward. The radiator needs to be removed (a lot more work) with the 4 blade.

I would never use a 4 blade myself.

[Rosenkranswa]

I would agree with Neil, in fact have been considering replacing the 4-blade on my pickup with a 2-blade but having to move the radiator to effect the changeover has stalled me. I'll probably bite the bullet and change it out this summer.

[Bob C]

The original two blade is not a safe fan to use. Go to Fordbarn and do a search
and you will find many horror stories. This is a pic of one I had.

[Neil Wilson]

Reproduction two blade fans work great (except for being original). If someone is considering a four blade fan, then they are not concerned about being original. For those wanting to be as original then there is not choise.

[Rob MacDonald]

The original two blade is not a safe fan to use. Go to Fordbarn and do a search
and you will find many horror stories. This is a pic of one I had.

There was a very well-written article about this in the Restorer some years ago. the fan has an inherent design flaw that will eventually lead to stress cracks and catastrophic failure. the preventative modification seemed simple in the article but I'd have to read it again...

[E.Moore]

The original two blade fan is made of two pieces of steel that are spot welded together. At the hub the two pieces are often not completely sealed together, alllowing moisture to get in between the fan hub and the fan blades.

The blades flex with rpm and can also separate along the seam. As time goes on and with heat from the engine/radiator and high humidity, rust forms and will stretch the metal at the hub, causing the fan blades to become weak at the hub.

This can be detected by feeling a known good fan around the hub and feeling a known bad fan at the hub. The fan will break as shown in the previous photo, damaging the radiator, hood, and anything that is in the way of the flying projectiles.

Some have been seriously injured while observing or working on the engine with a bad fan while the hood was up and the engine was running. Get to know this condition on the fan and you can prevent a sudden catastrophe.

These fans worked fine for decades and have only been known to do this since the 1960's. and are just as safe as any other fan once one knows and takes precaution against this situation.

[rsierk]

I agree with Mr. Moore. These cracks are easy to see, and in my over 40 years with Model A's I've never had one fail, but I have detected some starting to crack. These I have repaired. There is usually a distinct wailing sound emitted from them when the crack is flexing when running. People may think it is a generator bearing, but does sound somewhat different and is more engine speed dependent, that is, it changes more with engine speed change than a bearing does. I weld them with low carbon steel wire and oxy-acetylene torch and then anneal the weld afterward (opposite of quenching).