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Old 03-25-2013, 11:55 PM   #235
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City: SF Bay Area
Country: USA
Vessel Model: Tollycraft 34' Tri Cabin
Join Date: Feb 2011
Posts: 9,214
Originally Posted by Northern Spy View Post
Honestly, my recommendations aren't worth a heck of a lot, I just pulled out some ebooks at lunch today and copied and pasted a handful of items to add to the discussion.

That said it would seem that adding zinc dialkyldithiophosphate (ZDDP) MAY make sense if you have regions of boundary lubrication such as a tappet valve train, AND it is a gas engine. But it already has it in there, why do you need to add more? Just change the oil regularly.
From much I have read and what good mechanics I know tell me: Zinc content in gas motor oils has been greatly reduced due to ever tightening EPA requirements and newer engines’ roller bearing lifter bottoms reducing need for a zinc-barrier in oil. Classic engines (pre mid 90s) having flat bottom lifters (tappets) really need zinc in the lube barrier to fully separate cam lobes from tappet (lifter) bottoms. Otherwise the lobes are prematurely flattening and tappet bottoms are cupping toward eventual wear out. These mechanics are often rebuilding old classics due to that failure point of metal contact, wherein lube oil with too little zinc in it was used for too many miles. ZDDP is best zinc additive I've found. And, I use HD Valvoline Diesel dino oil in all my classic V8s because it too has better zinc %age than than gasoline engine motor oils.
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