Under such a slim cowling, there is not much room for a cooler. I have been searching for something slim, light and inexpensive. This is what I came up with.
Obviously this is designed for transmission fluid, but in an engine with a dry sump and external oil tank, the oil return line has no pressure above atmospheric, so I think this is safe enough. Frustratingly, the JEGS company is less than a mile from the airport, but they will only ship via UPS so I had to pay shipping too.
With the end caps removed, you can see that this is quite a sophisticated extrusion. There is a center baffle that runs the full length of the cooler with a hole at the far end for the oil to pass from one chamber to the other. I was also impressed that the there are fins on the inside to provide as much surface area as possible. In fact the total cooling area is significantly larger than the usual Harrison aviation oil cooler.
I drilled and tapped the end-cap to accept larger AN-8 fitings ( 0.5 inch ID), since this is the same size used for the oil return on the engine. I also substituted AN fittings for the brass ones supplied by JEGS. My engine may be old, but it is not a steam engine!
SCAT tubing with an ID of 3 1/4 inches slides nicely over the outside of the cooler. I will mount it onto the right side of the engine, and connect the other end of the SCAT tubing to the former carburetor air inlet on the CASA nose bowl. By a stroke of luck, it is also 3 1/4 inches in diameter.
I'll post the results of flight testing soon.