0W40?

[Paul Workman]

Originally Posted by Hib Halverson

Playing the devil's advocate...

LT5s with stock valve train don't need that level of zinc and phosphorous (which was formulated with pushrod valve gear in mind) because the cams act directly on the tappets. There are no pushrods and no rocker arms. That means less mass and since there is less mass, even the stock 1G LT5 valve springs have significantly less tension than valve springs in pushrod engines, thus the pressure over the nose is less and...there is less need for the extreme pressure additive ZDDP.

I no longer have Mobil 1 data sheets going back to the 90s so I can't quote facts, but I'm not convinced that all the factory fill oil used back then has 1200-1300 PPM phos.

NOT necessarily taking exception to what you stated re lighter mechanicals, i.e., pushrods and rockers, and spring tensions, etc. But, but, but! In the interest of physics, does not the forces to overcome inertia increase @ the square of the rate of acceleration (of the parts involved), AND therefore the task of the lubricity in the oil?

Again, the issue is direct vs. indirect "testing". Direct testing on the 1G LT5 is cost prohibitive, especially considering the lack of new or substitute parts. And, it takes significant runtime/stress testing to gather evidence enough to make any scientific, definitive conclusion(s). So, in absents of direct testing, we're relegated/obliged to accept INDIRECT test data results gathered with other (engines) operating with identical or at least practically close conditions.

My point is, the data for making a direct comparison(s) and much less predictions between results of this latest (Mobil 1) oil and that of products having considerably more real runtime data on actual 1G LT5s rests solely on a manufacture's reputation and little if anything else - comparatively speaking.

EXAMPLE: Various antifreeze makers provided a revolutionary coolant (referred to commonly as DEXCOOL; a coolant improvement over the traditional (GREEN) silicon base coolant which "Dex" superseded. But, if one were to replace their GREEN stuff with DEXCOOL solely on the assumption that the "DEX" was made by a reputable company and therefore suitable for their LT5, they were in for a very expensive mistake. Companies like Mobil 1 make a variety of products for various applications. But, applications differ, and one size does not always fit all!

Your mileage may vary....