Greetings,
At the time, I performed the Great Rust Off corrosion test, I assumed that non detergent 30 WT oils were the same or very similar.
I selected the Chevron 30WT oil because it was conveniently available and because my father and others recommended testing 30 WT oil against the other high tech products.
However, Rob Hoffman, a member of the Smithy Machines group, has convinced me that the Chevron 30 WT oil is not like a typical 30WT oil due to its formulated additives.
What follows is an email from Rob in June of 2009 with his test results and photographs that should be definitely considered as the finish of your machine may be at stake:
Ned...
Please excuse me for sending this to you outside of your group as I did not want to start another thread on this topic. You may do with these results as your program dictates and with my permission to use however you see fit.
Test object...mild steel mower blade sanded bright and degreased with TSP. Completely dry and clean before test subjects were applied.
Test coatings: Nothing. Control area in center of blade.
BoShield T-9 Spray
Accell Brand 30 wt, ND motor oil (Walmart)
http://www.home-machine-shop.com/Rob_H_Test-1.JPG
The surface was exposed to rain, saltwater, sunlight and outdoor conditions for one week after a single (liberal) application of the test coatings. Test conditions included laying out on a dock, riding on the bow of my boat and being carried on the bumper of my truck for about 1000 miles. Care was taken not to touch or disturb the coatings other than the environmental exposure factors.
I think the results speak for themselves. The Motor oil was better than nothing, but not much better. The BoShield was not perfect, but easily out-performed the straight-graded mineral base Motor Oil.
http://www.home-machine-shop.com/ROB_H_Test-2.JPG
I'm thinking that the Chevron Oil you used in your test had their usual additive package in it, but they have not responded to my request for information regarding that...I did send them an email, but as yet they have not sent me anything.
The Accell Motor oil is a pure mineral oil according to it's published spec sheet which is available on line. It has no additive package at all. The additive packages in motor oil vary a lot, but most contain anti-corrosion chemicals that I suspect were more responsible for the results you obtained in your test that any inherent properties in the mineral oil base stock.
So, I would have to take issue with any flat statement (or test) that found that "any good `ole cheap 30 wt ND Motor Oil" (with no additive package) was the runner-up in any rust prevention contest while competing with specialized products designed to do that job. From my test, I'd say the Accell Motor Oil would be close to the bottom of your list, which leads me to suspect that the Chevron Oil you used also had some very effective chemical corrosion inhibitor additives in it that actually did the job...not the oil itself.
Best Regards...!!
Rob Hoffman In Tennessee