Guys,
I suppose that there are always exceptions to the rule. That is why I said that "such damage might be possible". Most likely improbable in my estimation.
While I agree that POA/POEs pose little threat, the other additives like detergents, ZDDP, and MoS
2 are unlikely to cause damage to any finish that I can think of save maybe a cold blue that is "chemically delicate" and susceptible to attack from a host of many other corrosive agents as well.
Outside of the EP/AW additives, motor oils contain viscosity improvers and anti-oxidative components that I suspect pose little threat to most firearms finishes and their component materials.
I find the statement...
"a rep. from Pennzoil actually called me! ... the Pennzoil rep. said that while motor oil will work on most weapons, it will not provide a good level of protection from the elements, because motor oils are designed for use in a closed assembly. They will attract dirt and dust like a magnet for the same reasons. He did state that his biggest worry would be that the additives in motor oil may not be compatible with certain finishes. He stated an example of synthetic motor oil causing damage to chrome-plated parts in an experimental engine being tested."
...rather vague since the "rep" fails to qualify exactly what in the synthetics' formulation caused the chromium plating to fail in the experimental engine and his statement regarding the affinity exhibitted by "motor oils" for dust and dirt is true not only for motor oils but also, for the firearms-specific lubricants as well.
His expressed concern for the oils action upon "certain finishes" provides us precious little information and such commentary suggests that "they" (being Pennzoil) may be concerned with the potential liability of giving folks "the green light" to use their product in an otherwise unintended fashion and let's be truthful here, using motor oil as an alternative small arms lubricant is an "unintended and unauthorised" use.
As for the "too thin" qualifier, there are several grades of multi-viscosity oil that range significantly in their viscosity (please refer to post #1 for those numbers) from very thin like the 0w20 to very thick like the 20w50. I have never seen any issues relating to oil oxidation as it relates to the use of M1 on any of my weapons and while it is definitely a remote possibility, the frequency with which weapons are cleaned and lubricated can alleviate such concerns. In the nearly thirteen years that I have been using M1 it has seen several varying environmental conditons on at least three different continents and never have I ever had a weapon experience any "down time" or corrosion that could be attributed to "oxidized" M1. My weapons which range from nearly corrosion proof Glocks and HK USPs to blued Winchester Model 70s to Arsenal AKMs with their factory original bulgarian craptastic spray paint finishes have never seen rust,finish damage or corrosion as a result of M1 being used on them.
ETA:
From Grant Cunninghams' site-
Motor oils: Generally good boundary lubrication (particularly the Havoline formulations), but very poor corrosion resistance and poor resistance to open-air oxidation. In addition, their pour-point additives often contain benzene compounds, which aren't a good thing to have next to your skin on a regular basis! ATF is better on every count, even if it is a tad more expensive.
Mr. Cunningham fails to point out that ATF, synthetic or minerally derived, also has pour point additives and viscosity modifiers within its formulation as well. Furthermore, synthetic motor oils utilizing Group III, IV and V PAO basestocks typically require less of these additives and modifiers to achieve their required ratings since the Group III, IV and V PAO basestocks possess a large majority of these qualities to begin with.
Within the same article Mr. Cunningham also advocates the addition of STP Oil Treatment to ATF in order to thicken it should the reader find it "too thin" for their liking.
If you really want a thicker oil with all the good characteristics we've covered, mix ATF and STP Oil Treatment in a 40/60 ratio.
What Mr. Cunningham fails to realize is that STP Oil Treatment is nothing more than a polymeric viscosity modifier (it also contains ZDDP), compounds that he finds to be in undesirable quantities in synthetic motor oils. I am uncertain as to why he would suggest the addition of these compounds to an alternative that possesses less of them while cautionng against the use of synthetic motor oils for the very same issue.
ATF (synthetic or dino) is also designed to be used within an "enclosed environment" and as such is also not immune to the same oxidative stresses that could cause oxidation in synthetic motor oils.
His article is an interesting read, but I would be hard pressed to call it an authoritative treatise on the subject.
How about we take the simple act of putting something slippery on our boom sticks and make it really complicated? 