"Bass, Jerry" wrote:

Thanks, if I modify the duct as you suggest, will the air move forward,
towards the front of the cooler?  Some who have looked at it say the air
only goes toward the rear.  I have enlarged the air inlet from 2 sq. in. to
8 sq. in.  and blocked the bypass to not bypass with no improvement

Jerry Bass

That's why you need to skinny the back of the duct down a bit.
A straight wedge shape works fairly well but not as well as duct
that is thinned down near the back. Get one of those digital wind
meters and pump some air into the duct with a furnace blower. 
Use the wind meter to survey the air velocity coming out of the 
back side of the oil cooler. Here is my test set up for radiators.

Paul Lamar
 
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