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BigKev:

Replacing a mechanical engine-driven fan with an electric one will NOT improve engine colling at idle and low speeds. It will make it worse. Let me explain.

Modern manufacturers use electric fans for several reasons:

1. Their rpm, and therefore their air flow rate, is independent of engine rpm, and can be either fixed or electrically variable

2. They use less power than an engine driven fan, especially at higher engine rpm

3. They can be disconnected altogether rather easily when maximum acceleration is desired (just like an air conditioning compressor)

However, they are INFERIOR in actual air flow capability comapred to an engine driven fan. To understand why, you need to examione the physics.

One mechanical horsepower is equal to 750 electrical watts. In other words, it takes 750 watts to make just ONE mechanical horsepower. And that's only in a perfect world in which there are NO losses - i.e. the electric motor stays COOL and the wiring does too! In reality of course, there are losses that necessitate MORE than 750 watts of electricty to make one horsepower.

Since watts = volts x amps, at 6 volts, you would need 750/6 = 125 amps of electricity to the fan to make just ONE horsepower! Even at 12 volts, you would still need 750/12 = 63 amps!

The very LARGEST and MOST POWERFUL electric fans I know of consume just 30 amps (after the surge startup current which is always larger). SDo, even at 12 volts, they make at MOST (in only a perfect loss-free world of cold motor and cold wiring) only 12 x 30 = 360 watts of mechanical power. That's less than HALF a horsepower.

A mechanical engine driven fan on the other hand is driven directly by an engine that makes MULTIPLE horsepower, even at idle. You can make such a fan as powerful as you like, understanding of course that as the engine speed goes up, you will be consuming ever larger amounts of MULTIPLE horsepower to drive that big fan, and that will affect both acceleration and fuel mileage. Hotrodders often change to electric fans precisely to cut these power and mileage losses, BUT they sacrifice air movement in doing so. This is why so many hotrods ?run hot?!

The fans on our Packards are HUGE ? they are 20 inches in diameter ! That is way larger than even the largest electric fans, which are only 16 inches in diameter ? precisely because it would take too much electric current to run them if they were any larger! Since the air movement of a fan is proportional to both rpm and the SQUARE of the diameter, a 20 inch fan will, all other things being equal, flow 56% more air than a 16 inch one! Packard made the mechanical fan huge because (a) we NEED strong cooling at idle and low speeds, and (b) they COULD since the engine makes plenty of power ? much more than an electrical circuit could supply.

While the slightly increased fuel mileage and power of an electric fan would certainly be nice, I am unwilling to compromise the cooling at idle and low speeds to get it, since the cooling at idle is already marginal.

A much better idea is to add a shroud. A shroud would improve the air flow VERY dramatically. If someone offered a shroud kit for our Packards, it would sell like hotcakes, since our inline 8 engines are proven to need even more cooling at idle and low speeds than they currently get from the large mechanical fan. As it is, since no shroud kit exists, Randy and I will need to fabricate or adapt one. I intend to.

Jim G

Jim. That's EXCELLENT critical analysis.
On my 56 V8 Exec. I tried and electric fan WITH a 6 blade aftermarket fan on the water pump. I found that the electric fan in front of the condensor served little or no effect. In real hot weather of 100+ degrees i believe it only restricted air flow. At idle it showed no improvement. I think it only created a restriction.

THE PROBLEM is that he condensor sets about 1.5 inches FORWARD of the radiator due to the horse collar diagonal brace. Look at most cars with AC and the condensor is nearly up against the radiator.

I shrouded the condensor to the radiator and noticed some improvement worth the effort.

I have not yet come up wit h a good engine fan shroud arrangement despite repeated tries with various plastic modern shrouds but didn't really delve into the fitting like i should. Problem with the V8 is that the engine fan sets excessively to the right of the radiator.

I'm glad u brought up the engine fan shroud idea. I'll try to get busy on a fit for the V8's.

Back in the late 50's and 60's before the plastic revolution i saw at least 3 cars built with fan shrouds made from zinc wash tubs. I don't remeber how they atached mounting bracket tho. I'd rather use plastic shrouds that are commonly available because it is lite.

Go to the junkyards and look at old Fords, Chevys, Dodges, etc. I remember several of those vehicles having a simple two piece steel shroud that would be easy to adapt to almost anything. You'll be looking for '50s and early 60's cars.

I have one like this: 1963 Impala fan shroud


But it's in two pieces. As long as the diameter's right, you can make the mounts any way you like.

On the subject of electric fans, I have to say this: On my '49 Hudson pickup I built, I used a 429 Ford with C6 combo to power it. I also used an aluminum radiator and fan assembly from a '97 Dodge Caravan mini van that originally had a 3.0L V6 or the like. It NEVER overheated, not even once. The secret? It was a modern, dual fan arrangement with a built in shroud. I set it up so that the slow speed fan came on when it hit 160 degrees, then the second fan came on when it reached 190 degrees. Simple thing to do, as you can look at the temp ratings of temperature senders and switches in most parts books, especially Standard, Wells, and a few others. Run them through a relay, and you're done. This little radiator wasn't more than 1" thick, and approx. 34" wide and 18" tall, if I remember correctly. It never overheated even on 100+ degree days and with the notorious Kansas 100% humidity.

And it would burn rubber like no tomorrow!!:

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