I'm looking at a Mobil spec sheet I have, dated June 2003, for "Mobil Drive Clean Oil," their conventional non-syn, non-blended product. All of the five multiweights covered have flashpoints listed at 392F. The 5w-20 is the same as the 20w-50, so I'm wondering if they didn't make an error here. Their other oils (blends, etc.) will presumably have different flashpoints.
As well as having significance to firefighting, flashpoints are but one indicator of a oil's base stock quality, its resistance to oxidation (burning), and the likelihood that it will leave deposits (a lesser likelihood of oxidation or vaporization will likely lead to fewer deposits). As a rule, the high-end oils have high flashpoints, and vice-versa for low-end products, so there is relevance as to how the oil will perform. I once had a friend who raced a modified, hot-running, non-water cooled turbo Ford Thunderbird several years ago with a sports car club I was in. Not to bad-mouth MDC, but that might be but one good example of an application where other oils would certainly be a better choice than MDC.
[ December 17, 2003, 06:06 PM: Message edited by: TC ]