Today I replaced my big block a/c car's 7 blade GM deep pitch fan with Dorman 602-148. The Dorman unit has 12 blades, turns the right direction, but is 1" smaller diameter and has less blade pitch.

In early testing, the Dorman unit pulls much less air across the radiator than the GM 7 blade, but it's a lot quieter. Noise is why I wanted to replace the GM unit.

With the Dorman fan in place this afternoon, @78F, my car at idle got over 200F in about 15 minutes. By contrast with the GM 7 blade, I drove it with A/c on at 85F a couple of months ago for 6 hours and it never got above 195.

For heat rejection the Dorman is substantially worse than the noisy GM 7 blade, but a lot quieter. I was hoping it would be quieter & still keep the car 180F plus or minus.

Anyway I'm probably headed back to the GM 7 blade fan, but wanted to let you all know about the Dorman being both quieter & allowing the motor to run hotter.

This car has a 1966 fan shroud in place, augmented to cover the full width of the radiator by adding in a bit of Toronado shroud cut to fit. Plus the rubber mastic flaps and other blocks to force air through the radiator...

Short Version: Dorman 602-148 - hotter, but quieter. GM 7 blade deep pitch - cooler, but noisy.

 

I think you are comparing two different situations: idle and at-speed driving. The fan will be more critical at idle where it is the only thing moving air over the radiator; when at-speed the vehicle's forward velocity moves air across the radiator.

 

Great point, should have mentioned that in that trip in traffic it didn't get over 195. Which is more similar to the idle test this afternoon.

 

Maybe you just need to replace your fan clutch. It may be too stiff.

- Eric

 

+1 Fan Clutch. Once it gets warm, but not hot enough to engage the clutch, the fan should be very quiet.