One of the most important factors in successful engine operation is to keep the water at far below the boiling temperature. This is best done by matching the radiator with the fan blade.
On 1939-53 Chevrolet trucks there was a change in cooling fans depending on the demands the truck might have. The following three fan blade assemblies were as follows:
15“ Diameter 4 Blades
Standard equipment on ½, ¾, and one ton. Matched with 3 core radiators.
18” Diameter 4 Blades
Placed on most 1 ½ and 2 tons. Matched with 4 core radiators.
18” Diameter Heavy Duty 6 Blade – Optional
The Chevrolet Master Parts Catalog defines this fan “for use in low speed operations”. It was available on 1 ½ and 2 ton that would require slow moving or much of their RPM’s at idle speed.
Examples: A fire truck setting at idle speed while running the pumps to furnish water through their long hoses.
A flat bed farm truck during hot summer days. It slowly moves in a field while hay bales are loaded at almost idle speed.
No doubt at higher RPM’s this 6 blade fan would create extra wind noise under the hood but, after all, it was the price you paid to have a non-boiling radiator. (And it did the job successfully)
Overheating ½ or ¾ ton? As calcium builds up over the years in engine and radiator, heating problems may surface. As a “Band-Aid” to get by for a while, some owners install the larger 18” fan. With more air passing through the radiator core, major repairs can sometimes be postponed.