Called BS on synthetic oil for 10 years until a teardown proved me wrong

I used to swear by conventional 15w40 in my old Cummins 5.9. Ran it over 300k miles with cheap Rotella T. Then I bought a truck from a guy who only used synthetic Rotella T6. Pulled the valve cover at 200k and the difference was night and day. No sludge, no varnish, just clean metal. I still think synthetics are overpriced but that visual convinced me it matters for long term. Anyone else change their mind after seeing something firsthand?

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1 Comment

jake_dixon12h ago

Man that's the exact kind of thing that made me switch. Seeing is believing, right? I had a buddy who ran a 7.3 Powerstroke on conventional for 400k miles and it looked like a greasy mess inside when he pulled the heads. Then another guy with the same truck on synthetic and it was like looking at a brand new engine. The heat cycling thing makes sense to me now too, synthetic handles the hot cold swings way better. Still hurts to pay the extra cash but I figure it's cheap insurance compared to a rebuild.