slant 6 oil weight

nm9stheham said
Amen to the lighter oil in the 7.3L and 6.0L in winter!

Can't explain the 'don't use synthetic due to leaks' in this day and age. When Mobil 1 first came out in the 70's, only lighter weights were produced and older engines did have some leaks. But the newer variety of synthetic weights has fixed that; it is just 40+ years old old experience hanging on...
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And yet it still works, and for a lot cheaper. Why do you think newer engines use Viton seal material if neoprene would seal synthetics? I've tried synthetic oil and see no benefit in my old or new cars. Spend all the money you want and tell yourself it is better.