"SM" allows more zinc, for oils that are outside the "normal" 0-30 range.

Here's what I found when I dug into the spec's:
https://rennlist.com/forums/928-foru...ml#post5724722

 

SM has other antiwear additives, but the levels of zinc, phosporous and sulfur are still like SL, at least in US. It's the CF-4 certification that definitely requires lower levels of these compounds.

 

Thx everyone for the input. This has given me a little food for thought. I will do more research.

 

Mark, Sorry for the confusion...Sean posted "If you've been using it for 23 years, no reason to change it. " to which I responded "IT changed" The fact the the old synthetic and old additive package was used for years does not mean the current stuff is as good ! Mobil just hopes you think it is...... since it costs much less to make it from petroleum base.

 

Some ZDDP reading...

http://www.blackstone-labs.com/Newsl...ber-1-2010.php

 

interesting read.......test was for only 3800mile on a new engine with flat tappets and as the author readily admits all he has done is analyze the oil... lets see what the cams look like after 10k and further out and use an identical set up with oil with zddp for a control . that would be closer to a limited "scientific method" way to test his null hypothesis.

It is neat someone is actually trying to think this through....I bet someone has really done the testing and has reported it in an engineering peer review journal.

thanks for the blackstone post ...pretty neat.

andy