I've been daily-driving a 2005 400ex for a year now and it needs some extra cooling for street driving. I have an extra oil cooler from a 250ex, which appears to be the exact same thing, just one row shorter. My plan is to run the out from the 4 row cooler to the in of the 3 row, then out the 3 row back to the oil tank. This would give a 75% increase in cooler size, but im worried about pressure loss. Anyone have some experience with this? I mocked up the cooler where i want to mount it;

 

This guy used a tranny cooler from a 350 Chevy. says he had a 30F-35F degree drop in oil temp.