Was dead set against using synthetic oil in my old 5.9 Cummins until a fleet manager showed me the tear-down after 300k miles

I always thought synthetics were a waste of money for older diesels, but that engine had almost zero wear on the cylinder walls and bearings, so I switched both my trucks over last winter and haven't looked back, has anyone else seen proof like that change their mind?

2 comments

2 Comments

charles9191mo ago

Been running Rotella conventional in my old 7.3 Powerstroke for 15 years now and it's still chugging along at 280k without a rebuild. Not saying synthetics are bad, but I wonder how many of those clean tear-downs are just from people who actually change their oil on time instead of stretching it out. Seen plenty of high mileage conventional engines that looked fine inside too. Plus that old Cummins probably had way better maintenance than the average truck, so maybe the oil wasn't the only factor. Still, I get it, seeing is believing, just not convinced it matters as much for guys who already take care of their stuff.

parkerh381mo ago

280k on a 7.3 with conventional is solid proof that regular oil changes matter more than the label on the bottle. But here's what I've been chewing on - how many of those guys running synthetics stretched their intervals to 10k or even 15k because they thought the oil could handle it, then ended up with sludge anyway? I've seen that happen more than once where a guy brags about his 10k syn schedule but his valve covers tell a different story. So really, isn't the whole debate more about drain intervals than whether you're running dinosaur juice or lab stuff?