Oil Cooler Orientation

The Horizontal or Vertical choice is whatever esthetics work for you.
Not optional is that the Outflow port is ALWAYS Uppermost.
In the Horizontal orientation, either port can be the Outflow as they are both on the top. NEVER on the Bottom.
In the Vertical orientation, the Upper port need to be the Outflow or you will trap air in the cooler causing reduced efficiency.

Roger Lee wrote:

"You have not given any rational for your suggestion - why horizontal?"

Because I have to remove fittings and or hoses quite often and vertical would make that difficult, messing and likely an oil purge. Depending on which fitting is up that may trap air in the top of the cooler even with a purge. It has nothing to do with the cooling. I'm not saying it can't work just the horizontal is better.

Lost my fuller answer!!!

In brief - as long as the efficiency of the cooler is maintained (the critical point), I believe the vertical orientation (hose fittings on right side) would in fact make hose fittings more accessible, facilitating removal/replacement, air purging easier & more assured,  making maintenance/servicing easier, .

Bill Hertzel wrote:

The Horizontal or Vertical choice is whatever esthetics work for you.
Not optional is that the Outflow port is ALWAYS Uppermost.
In the Horizontal orientation, either port can be the Outflow as they are both on the top. NEVER on the Bottom.
In the Vertical orientation, the Upper port need to be the Outflow or you will trap air in the cooler causing reduced efficiency.

Agreed -

There was never a possibility that the plumbing lay out would have the incoming (from reservoir  going anywhere but the lower "port".

Upper port, outgoing cooler oil,  to engine oil pump.

I have never experienced it myself but I can see how having  the two oil "ports" at the same level may cause a purging failure/problem.

Our oil cooler is horizontal, with two 90 degree elbows at the top entrance/exit fittings. One of them has serious rubbing wear on the top side, in contact with the cowl. We're going to have to replace them. Make sure you have adequate clearance!