Swapped to synthetic oil after 10 years of conventional, big difference

I always ran conventional 15w-40 in my old Cummins 5.9, figured it was fine for a 90s truck. After reading some forum posts I tried Rotella T6 synthetic about 6 months ago. The cold starts this winter were way easier, maybe 5 seconds less cranking at 20 degrees. I also noticed the oil pressure stays more steady when towing heavy loads up grades. Just my personal experience, but has anyone else seen better fuel economy after switching to full synthetic in an older diesel?

2 comments

2 Comments

coleman.jade1mo ago

Yeah that first cold start after switching is the moment it really hits you. I run T6 in my 05 F-250 with the 6.0 and its amazing how much less drama there is when its below freezing. The oil pressure staying steady under load is something I noticed too, especially pulling a gooseneck up some steep grades in the summer. Your buddy's story about the 7.3 is exactly what I hear from most guys who finally give synthetic a try.

the_fiona1mo ago

Man I had a buddy who swore he'd never switch from conventional in his 7.3 Powerstroke. He finally did after his glow plugs started acting up one winter. First cold snap after switching to Rotella T6 his truck fired up like it was summer, no grunting or white smoke. He said it paid for itself in one season just saving him from cussing at the dash every morning.