Old timers swear by break-in oil but I keep seeing folks skip it on rebuilds

I pulled apart a 6.7 Cummins last month that had 20k miles on a fresh rebuild and the cam lobes were already showing wear. The guy who built it told me he ran conventional 15w40 from the start, no break-in oil. Am I wrong for thinking you gotta run that high zinc stuff for the first 500 miles or is this just old school paranoia?

2 comments

2 Comments

the_robert27d ago

Gotta run that high zinc stuff for the first few hundred miles at least...

the_mia27d ago

My 454 build went 180k miles on cheapo Rotella 15w40 with zero issues, and that was a flat tappet cam too. Thats a lot of miles for something that supposedly needs special oil from the first fire up. I think @the_robert is right about older stuff needing it, but modern oils are way better than folks give them credit for. A lot of the zinc panic came from people parroting what they read online instead of just running their engine and seeing what happens. My only rule is change it often and keep it clean, and that has never let me down.