Coworker swore by synthetic oil for older diesels, I told him he was crazy

I've been running conventional 15w40 in my 7.3 Powerstroke for 12 years now. A young kid at the shop last week said I'm losing power and fuel economy by not switching to full synthetic. He showed me his oil analysis reports from two different intervals on his 6.0, said his wear metals dropped by half. I always thought synthetic was just snake oil for high mileage engines. But now I'm looking at a 3 mpg difference between our trucks doing the same hauling route. Is he right or am I just old school stubborn? Has anyone else switched after years of conventional and seen real numbers?

3 comments

3 Comments

river32025d ago

Nah the kid's got a point. Synthetic oil handles heat way better and cleans out sludge that conventional leaves behind. You won't notice it at first but after a few thousand miles it's a different engine. The 3 mpg difference isn't just oil, could be his truck's tuned better or he drives lighter. Wear metals dropping by half is a real thing though, C&P told me the same thing when I switched my 6.0 five years back.

susan13025d ago

You're leaning hard on that "wear metals dropping by half" stat but those tests are usually done by companies selling synthetic oil. Run the same test ten years later on an older engine that's never seen synthetic and you might get gasket leaks from all that "cleaning" it does. Swapping my 5.3 to synthetic at 120k miles just made it start burning a quart every thousand miles, never had that issue on conventional.

carter.laura22d ago

@river320 coming in hot with the "just wait a few thousand miles" advice like that old truck's gonna magically turn into a race car. @susan130's story about the oil burning is exactly why I'd be scared to touch a 7.3 that's been on the same diet for over a decade. Synthetic's great and all, but switching now is like convincing your grandpa to start drinking kale smoothies - maybe it works, maybe his gut just explodes. The 3 mpg difference is probably the 6.0 being a newer platform too, not just the magic juice in the oil pan.