I just got done installing an auxiliary oil cooler on my 82 Westy 1.9NA. I
got a deal on a large 8X13 cooler so for now the only place I could find was
on the floor area below the sliding door (not the best place for protection
IMO but OK  for a highway trip). Former oil temps with the stock cooler ran
up to 270F. Removing the stock cooler and running just the aux. showed a
disappointing  250F max. Running the stock cooler AND the aux. cooler dropped
temps to 230-240F on a long pull which I can live with on this trip. Oil
pressure is better too.

BTW another listee with a 1.6TD Westy reported the same high oil temps. He
used about a 10X10 cooler behind the right tailight, ducted and with an
electric fan. He reported temps constant at 210F. Don't know if he kept the
stock cooler.

Hope this helps someone.