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Is it possible for a fan shroud to be too big?

pityocamptes's Avatar
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Join Date: Aug 2001
Posts: 40

07-23-04, 08:58 AM   #1  
Is it possible for a fan shroud to be too big?

I have a '74 International Scout II w/AMC 258. It never had a fan shroud and someone suggested that I add one since the rig seemed to run a little hot while creeping (I live in Southern AZ and its hot). Anyway, my brother and I fabbed a shroud out of sheetmetal (aftermarket parts are either too expensive or are not available for Scouts) and mouted it to the 4 core radiator. The shroud extends about 6" past the radiator and completely covers the direct drive fan blades. Now, while driving it seems to run cooler but it feels like I have a lot of wind resistance (or maybe losing horsepower). Someone suggested to me that the shroud might be too big and thus the fan blades are having to move a lot of air and robbing the engine of power. This person was saying that the shroud should only extend past the fan blades no more than 1/2". Does this sound right? Thanks.

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davo's Avatar

Join Date: Apr 2002
Posts: 2,417

07-23-04, 06:43 PM   #2  
A 1/2 inch past the blades would be about right but remember you now are pulling air through the radiator and from nowhere else so noise level and engine tone will seem different to you.I suggest you leave it alone if you have acheived the cooling effect you desired.

Desi501's Avatar

Join Date: Oct 2003
Posts: 2,207

07-24-04, 03:47 AM   #3  
You cannot pull too much air. That's determined by the fan's size and pitch. The goal here is to creat a type of wind tunnel to pull air through the radiator and only the radiator. Your shroud should seal off the radiator at the sides and not allow air in from around the outside of the radiator. The edge facing the engine should be even with the fan blades with ideally only 1/2 in clearance. This will create the wind tunnel type suction effect you want to accomplish. The fan should have a thermostatically controlled clutch that will minimize lost horsepower.

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