2 blade or 4 blade fan

[Gold Digger]

Getting read to change out the old engine for a new Burtz engine. I use a manifold heater in the winter and was quercous which one might blow more air. I've heard that the 2 blade done the most but not sure. Does anyone have a good answer on this mater.

[Phil Brown]

2 blade more than enough airflow and quieter
(with a good radiator )

[daveymc29]

Don't use an original unless for points show, use the new aluminum two blade which you might want to balance before mounting, but I have used several just out of the box and have had no problems with vibration, or anything else to do with them. They are a good product and there were some with the wrong taper, but I have never come across one in 30 years of using them.
Dave Mc Arthur

[old31]

I agree with dave 100%.

A 2 blade will blow enough air into the heater, so there is no need to go with a 4 blade.

[mcgarrett]

While we're on the subject, did Ford ever install the 4 blade fan from the factory? I haven't seen any factory photos showing a 4 blade, but maybe I haven't seen enough photos!

[Gold Digger]

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I'm sure I'll go with the 2 blade then, I like them for the simple reason you can change the water pump with out pulling the radiator if you use the bolt set up instead of the original studs. I to had wondered if Ford used the 4 blade in some cars and not in others.

[Joe K]

The other aspect which is frequently not considered is that with EITHER 2 blade or 4 blade, you get the car above about 20mph, and the velocity air flow CFM naturally EXCEEDS that of the fan when stationary. I.e. the fan actually holds back the air - or perhaps more accurately "measures it out."

So it may make sense that a 4 blade may hold it back MORE EFFECTIVELY.

I have a couple of aftermarket fans, a 2 blade I have used, and a four blade that came with the Gordon-Smith Compressor. Somewhere I have seen that Ford installed the 4 blade on trucks and industrial engines - and the Gordon Smith setup would qualify.

I've also seen that while less likely to fail than an original fan, even the period Western-Auto, Pep Boys, JC Whitney pressed metal fans can fail, commonly at the bolting holding the fan to the pulley casting. Rather not the bolting but the "weak spot" presented by the four drilled holes. The centrifugal force "tears" apart the sheet metal between holes.

My choice today is the Cast Aluminum two blade.

Joe K

[mcgarrett]

Joe K,
Thanks for answering my question about the 4 blade fan. Didn't know the back story about the installation of them only on trucks and industrial engines, which makes perfect sense. That also accounts for why I never saw any passenger car factory photos with anything but a 2 blade fan. Is this a great forum, or what?

[31a]

It has been hard to find the 2 blade for a while may have to do some searching with several vendors

[gdmn852]

Hello, One thing with the cast blades is sometimes they will rub on water pump casting and water pump may require some grinding for clearance.Don’t remove stock from fan . The reason they are thicker is because original was a pressed steel manufacture .

[Marshall V. Daut]

I wish I had taken photos of what my '31 Roadster's radiator core and top right-side hood panel looked like in 1990 after the four-blade fan I was running separated and one blade went ballistic inside the engine compartment. Not a pretty sight. I was living in hot Phoenix, Arizona at the time and thought a four-blade fan would cool the engine better than a two-blade. Mistake! After having the radiator core repaired, I installed a repo aluminum two-blade fan blade and that kept the engine cool even in Phoenix's notorious 115 degree summers. The critical element in a Model A cooling system is not necessarily the number of blades on the fan. A good core and clean engine passageways go a LONG way in helping the engine to run cool. Of course, all the other elements that can contribute to a Model A overheating have to be within spec, such as the ignition timing, properly adjusted brakes, unimpeded airflow through the radiator core (not blocked by large license plates) and sufficient coolant. If your Model A engine's cooling system is so borderline that you think using a four-blade fan will work, you are in for a big disappointment. And maybe a big expense.
The problem with those old V-8 four-blade fans is that they rust between the two blades, including the rivets that hold the two halves together. Enough time, rust and stress will cause the blades to come apart after all these years with disastrous consequences. Since that disaster 30+ years ago, I have removed more four-blade fans from Model A's I have worked on than I can count. And I will continue to do so. Into the junk metal barrel they ALL go. I understand that some antique car tours will not even allow Model A's with four-blade fans to participate because they are deemed so dangerous and are considered time bombs waiting to go off. That should speak volumes about whether one should use them or not.
Marshall

[McMimmcs]

Originally Posted by 31a

It has been hard to find the 2 blade for a while may have to do some searching with several vendors

I recently purchased a two blade from Snyder’s. Wayne

[Bob Bidonde]

After you have the fan of your choice installed, learn about the air flows doing this. Run the engine at a fast idle. Using a paper towel, move it around the front of the radiator to see where the max & minimum air inflows are. Then move the towel along the first few louvers of the hood. You may see that the towel is sucked inward at the first few louvers, then outward thereafter. My observations are with engine pans in place.

[David in San Antonio]

@Bob Bidonde - Air flow can be complex and counter-intuitive. The rear-engine Renault Dauphine has the radiator aft of the engine. The cooling air flows forward into the tail and exits out the engine compartment louvers. When people were hopping up VW Microbuses it was common practice to mount an oil cooler over the side louvers, with an air scoop sticking out. Some people faced the scoop forwards, some insisted it must face aft. I wonder which was better?

[DavidG]

mcgarrett,


To answer your other question, the part number of the four-blade fan was 46-8600 which was released for use in production during the 1933 model year. As a service part, it also fit the Model A and Model B water pumps.

[Gene F]

Ya know it amazes me that some topics just stir up a lot of advice, information, and even opinions. Every time the fane topic comes up I think of that. Some others; motor pans, oil viscosities and formulas, babbit, and carburators.

[JoeCB]

Can't help but wonder about all those Model A's with original fans that made it across the southwestern desert to California back in the 30's and early 40's.... loaded down with entire households of baggage.... 6 kids and a dog.

Joe B

[Marshall V. Daut]

"Can't help but wonder about all those Model A's with original fans that made it across the southwestern desert to California back in the 30's and early 40's..."

One possible explanation for their "success" during those times (or failures that we never hear about) was those parts and their metal were 70-80 years newer than they are these days. Metal fatigue, stress, rust damage, age, millions and millions of engine revolutions since the Great Depression, etc., have taken their cumulative toll on them, just as life does to us after 70-80 years. I am more rusty now than I was 60-70 years ago! When I was just starting out in Model A's in the mid-1960's, one rarely heard of fan blade failures. Heck, the parts were only 35 years old then, barely broken in! Add another almost 60 years of use and abuse on top of that and it's easy to see why we should not trust original fan blades anymore - two or four-blade.
Marshall

[Bob Bidonde]

Ditto Marshall's comments, and here is something to back him up. In my opinion, it is foolish to run an original fan for fine point judging. No matter how good an original fan may look, or what expert repaired it, an original fan is a TIME BOMB!!!!!!!!!!!!

[old31]

I have a 4 blade story. A friend of mine asked that I clean up his engine compartment and install a new water pump. He had a 4 blade, liked it, and wanted to keep it. It looked pretty good to both of us so he said just paint it.

Before painting what really looked like a nice fan I sand blasted it.

To my shock were two 1" long deep cracks on both sides of the fan. There was not much left to this fan, it was ready to go. There were so many coats of paint on the fan that the cracks were not visible.

So, as mentioned above. Get rid of the waiting time bomb and get a new aluminum 2 blade. No matter how nice the old one looks.

[Marshall V. Daut]

Here is something else to consider: Occasionally in the Model A classified section of this website - and especially in the V8 section, the home of the four-blade fan - people offer four-blade fans for sale, sometimes singly and sometimes en masse. Perhaps it's Schadenfreude for me because of my horrible experience with the d*mned things and because I have removed so many from Model A's before disaster struck, but I follow the sales progress of those fans. Or more correctly stated, LACK of progress. They sit there in the classifieds day after day, week after week, repeatedly being moved to the top of the stack every once in a while by the seller. I once offered five four-blade fans for a measly $25.00, i.e., $5.00 each. No takers from either classified section, day after day, week after week. The ad got very few viewers, too, which is a sure sign of desirabilty. Even V-8 guys are gun-shy about buying used four-blade fans for the very cars that came equipped with them from the factory! What does THAT tell us about four-blade fans?
The word is out...bad news!
Marshall