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Why does nobody talk about using the wrong oil weight for older engines?
I’ve been wrenching on my ‘92 F-150 for years and always used 10w-30 because that’s what the manual says. Then I talked to a guy at a parts store in Tulsa who said I should be running 5w-40 in summer due to heat and wear. He showed me how the thinner oil was causing lifter tick after 3,000 miles. Now I’m split between sticking with the factory spec or trusting real-world experience. Anyone else have a moment where a veteran mechanic called them out on oil choice?
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johnson.eva4d ago
Man that part about lifter tick hitting at 3k miles really got me. I had almost the exact same thing with my 94 F-150, ran 10w-30 for years then switched to 15w-40 in the summer and it quieted down a lot. Those old 302s and 300 sixes just seem to like the thicker stuff when the temperature hits 90+ especially if you've got some miles on the engine. I think the factory spec was written back when these trucks were new and engines were tighter, now with some wear the thicker oil helps fill those gaps better.
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coleman.hannah4d ago
Really hit me" is right, @johnson.eva. I heard a guy on a podcast a while back talking about how factory oil specs are basically written for a brand new engine with zero miles on it. Once you've got some wear, especially on those old pushrod motors, the clearances open up and thin oil just slips right past the rings and bearings. That lifter tick thing makes total sense to me now. I read a forum post where a retired fleet mechanic said he always went one weight heavier on anything over 100k miles and it cleared up a lot of issues. Feels like the factory spec is a starting point, not the final answer, especially for a well-used truck.
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davidshah3d ago
And that fleet mechanic thing checks out too, I've heard the same from old timers who swear by 15w-40 in anything with a few hundred thousand miles. It just makes sense the thicker oil fills in the gaps better when the engine's got some wear on it, especially in heat.
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