I'm still skeptical about modern oils without the zinc additive. The fellow holds up a camshaft and says that the synthetic oils can be used for flat-tappet cams but he doesn't say with what additive package. When I pulled apart my 235 that had a Crower Hi-lift cam, it did show some visible wear after ~100,000 miles. I had been using RPM DELO 15-40 and Valvoline 20-50 before that. I got DELO in 5-gallon pails and used it until they cut the additive package to accommodate trap oxydizers. Since then I have used Valvoline VR1 20-50 then Rotella T 15-40 with an added dose of ZDDP additive. We'll see how that works out. I have also used Costco's Diesel API CK 15-40 but the oil consumption is higher with that by about 40%. The VR1 also showed higher oil consumption.
Oil temperature stability is important to me as I regularly see 250 degrees F for maybe 1/2 hour to an hour at a time on hills and a steady-state 210F (think Ogden, UT to Laramie, WY on I-80 eastbound).
I need to have a 5,000 mi drain interval as that's typically how long my round trips are. I haven''t changed oil on the road, though I do grease the chassis when I get the chance.
