I was discussing the first few flights with some friends at the airplane a few weeks ago, and mentioned the oil temp had reached 200F after climbing 3500 feet from take off. That was on a sub 40F day.

My oil cooler lays fore and aft along the right cowl cheek, and all the air from the right cowl inlet serves this cooler. I built a nice divergent duct back to it, where the air must turn down and make a 90 degree turn to pass thru the cooler element. then it meets a louvered cover where the air turns aft 90 degrees to re-enter the free stream outside.

When looking into the mouth of the duct, you can see the aft third of the cooler.

 Bob K a retired Boeing flight test engineer suggested I put a vortex generator in the oil cooler duct to pull the air down along the divergent floor.

So I did! I made a "Hall" type vortex generator, right out of a picture in the Aircraft Spruce catalog, and stuck it into the center of the duct floor, at the start of the divergent part. I bent it up out of a scrap of .025" aluminum and stuck it in place with double sided carpet tape.

On my next flight, I noticed cooler oil temps generally, and specifically, no temps near 200F during the initial climb to 4000 feet where I have been doing most of my early testing. Cruise temps run about 185F. We'll see what happens as the weather gets warmer.