T.P. Stephens" <doktortim@ROCKISLAND.COM> wrote:

> I was aquainted with a petroleum engineer in the early 70's who explained
> to me the nature of the then new multi weight oils. The recollections of
> those discussions are as follows:
>
> 10W oil has less carbon content than 20W
> 20W  "   "   "     "      "      "   30W
>
> You get the picture. To make a multi weight oil say, 10-40, you use a
> straight low carbon 10w and add polymers and other alchemicals to provide
> the characteristics of the high weight rating. The lesson is, the lower
> weight the base oil, the less carbon, and the less carbon deposit buildup
> on pistons and combustion chambers.

The more/less carbon idea, while strictly true, is a bit misleading.  Oils
contain long chains of carbon atoms strung together.  The entire petroleum
industry makes its bread and butter cleaving the long-chained heavy oils into
shorter-chained lighter products.  "Cat cracking" means catalytic cracking of
those long chains (and has nothing to do with feline abuse ;-).

Longer-chained petroleum products will have a higher viscosity; shorter-chained
molecules will have a lower viscosity.  That's the primary difference between
oil grades (along with some other properties like vapor pressure,
combustibility, usefulness as a solvent etc.).  So to say that you will get
more carbon buildup by using heavier oils, IMHO, is not true.

The carbon deposit buildup that one seems are more likely gummy tars from
longer molecules created in the combustion process.  That's why stuff like
Marvel Mystery oil is popular...it's a solvent that removes that crap (or at
least claims to).

-Karl

Karl and Kristina Bloss, Trexlertown, PA
'87 Westfalia Weekender  "Beverley" - 189K miles
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