I have no idea how many miles I have on mine (well over 200,000) as my speedometer cable quit a long time ago, but I use 20-50 all year round in both my 81 and 03 (277,000).
My reasoning is that with so many miles the tolerances have increased to the point where a thicker oil will not cause issues. I also owned a 1968 bus that I ran the same weight oil in and that was while living in CO where it was even cooler than the east coast.




