An original fan is best for this job
I am restoring a 1955 Chevrolet 210 with the 265-cubic-inch small-block V-8 and standard transmission and have added after-market air conditioning from Old Air Products for those hot summer days here in Arizona. Now I am having a problem with overheating just when I need the air conditioning most. I have added a triple-core radiator, the engine has been flushed, and I have installed an after-market five-bladed fan to see if that would help, but it hasn’t worked. Would an electric fan on the front of the radiator do the job?
I too have a 1955 Chevy with a small-block V-8, and I added an Old Air system several years ago. And I too had the problem you just described, and discovered that the best way to solve it is to find one of the original fivebladed mechanical fans that Chevrolet used on their air-conditioned models.
In my experience, the modern mechanical flex fans don’t do the job. As it turns out, the shape and design of a mechanical fan is more complex and specialized than you might think—at least according to my son who has engineered huge air conditioning systems for hospitals and hotels.
The original mechanical fans used on cars are remarkably efficient. A fan shroud around them makes them ever more effective because it decreases tip turbulence and increases the velocity of the air flow. I have not added a shroud, but since I installed the original correct fan, I have had no more problems. I did the same thing to my 1958 Chevrolet Pickup when adding air and it has worked well in that application too.
An electric fan attached to the radiator is 25 percent less efficient than a mechanical fan in service except in slow traffic situations where you are stuck in traffic idling along, with very little air coming through the grille, and the mechanical fan is spinning at low rpm. And keep in mind that a puller electric fan on the back of the radiator is more effective than a pusher fan on the front of the radiator.
If you do decide to go with the correct, original five-bladed fan you may have to scour the swap meets and Internet for a while to find one and you may have to pay a premium for it, but it is probably the best solution to your problem. I paid $200 for one a few years ago and I don’t regret it. Make sure it is not bent though. Bent fans are dangerous because the bent blade will continue to flex in service, and can actually tear off. Many years ago I was the proud owner of a 1949 Chevrolet that had a big rip in its hood from an errant fan blade.
When you do attach the fan and its pulley on the front of the water pump, make sure all of the surfaces are clean; use only new lock washers under the mounting bolts; and take them down evenly in a cross pattern until tight. This is important because if you don’t take the bolts down evenly, the fan or pulley can become cocked or deformed slightly, and in service they can then come loose and destroy your radiator as described above.
Also, tension the drive belt according to the specs in your shop manual, because if it is too tight it may ruin the bearings in the water pump or generator, or the belt will snap. And if the belt is too loose, it will slip and squeal, and if it is loose enough, it won’t turn the fan properly and you will have heating problems.