oil cooler

[Porter]

Yes, it appears you need the adapter plate.

In regards to the numerous threads on coolers just a few first hand observations.
I delayed putting one on my Ultra due to these threads about not working sitting still, not needed when moving etc. i bought the HD one simply because I got a good deal on it. My Ultra would gradually creep up to the 300 degree mark after a couple of hours of hard riding so i felt I had to do something. After installing the cooler I see no temps. over 240 and to solve the sittting still thing I installed the manually operated Big Sky fan unit and would like to mention that the complete system works like a champ and I am totally happy with it. IMHO this is a needed item on any heavy big twin.

Do you have the lowers on your UC all the time?
I noticed a big difference on mine (as far as cooing goes) with the lowers off.
I don't have an oil cooler on installed on mine, but the temp readings on my McEwan temperature gauge mimic what you are describing, when I took my lowers off. I road from MD to NC with lowers on in one direction and off in the other. Air temps were consistent on both days at 87 degrees.