At 11:37 AM 1/10/99 EST, you wrote: >A few weeks ago I posed this question to Ford Lehman guru Bob Smith. His >answer follows: > >"I do not recommend the use of the multi-visc Rotella, or any other brand >for that matter. In order to meet the 15-40 parameters, the oil has >approximately 40% of it's content made of additives to make this happen. >Pay a little more and buy the straight 30W Rotella. > >The engine holds so little oil that paying a bit more vs wear on the >engine is a cheap price to pay. > >Best regards, > >Bob Smith > >Reply to: (bobsmithadc@juno.com)" > >Small wonder some of us are confused. I'm reminded of the saying that "advice >is worth what you pay for it." > First let me say that if you want to use a single grade oil, go in peace. If the estimable Mr. Smith prefers 30wt to 15w40, be happy. It is, however, troubling that he bases his recommendation on such specious arguments. The respective additive packages of single grade and multi grade versions of the same label oil (whether it's Delo, Delvac, Guardol, Rotella, or Ursa) have far more similarities than differences. The rule of thumb in the oil industry is that additives make up 25% of the volume and 50% of the price of the finished product. Why? Because petroleum oils by themselves just aren't very good lubricants. The difference between single and multis comes down to one choice of base stock components, that being Bright Stock vs Polymer. Bright Stock is a component of single grade oil that is used to bring the oil's viscosity up to the desired level. As I have mentioned in prior posts this extremely thick material was (past tense) thought to afford some residual protection to an engine at start up. Polymer is a component of multi grade oils that, as the name implies, is made up of very long-chain molecules that go into and out of solution with the other components thereby causing large improvements in the product's viscosity index. I explained in an earlier post why this is a good thing. Also, it has been my experience in the past that 15w40 is more expensive than 30wt, again primarily because of the price difference between Bright Stock which is almost a left-over from the refining process and Polymer which chemically has a fair amount in common with synthetic oil. It's been a while since I've been involved with pricing so I may be wrong about this. I'll check when I get to work today and if Bob Smith's version of pricing is correct I will apologise. Speaking of apologies: If I have quoted excessively or rambled incoherently I plead not guilty by reason of sleep deprivation. Good night. - ___________________________________________________________________________ | This is only temporary... | Alex Hirsekorn | | Unless it works. (R. Green) | alexh@gte.net | ---------------------------------------------------------------------------