RE: alfa-digest V9 #310

["Brian Shorey" <bshorey@domain.elided>]

<snip>
> their seals compromised by any modern multi-weight oil, whether it be 
> synthetic, semi-synthetic or pure mineral oil. Modern oils have 
> aggressive additive packages, with strong detergents and dispersants. 
> These are designed to keep all impurities in suspension so that they 
> will end up in the oil filter, not in the engine. Older cars, with 
> their single-grade oils depended on deposits around the gaskets and 
> seals to make them oil-tight because the tolerances weren't that tight

> in days before CNC machining.  An aggressive additive package will 
> dissolve these deposits and the seals will leak.  Also modern oil 
> viscosity such as that found in synthetics is simply too thin to work 
<snip>

I can't argue, but I do have a question.

I don't see what the viscosity of an oil, or the weight, has to do with
detergents and additives (with the exception of VE additives).  My
understanding is that something like Valvoline straight 40 weight oil is
basically the same as Valvoline 10w-40, with the exception of the
viscosity enhancers (VE).

So I don't see how a modern straight weight motor oil would be any less
'damaging' to vintage seals than a modern multi viscosity oil from the
same manufacturer.

I know plenty of people who are using modern synthetic oils in Alfas
built in the 50's and 60's with no problem, although, to be honest, I'd
imagine the engines in these cars have been rebuilt at some point in the
last 20 years or so.

I'd leave Redline out of this discussion, my understanding is that they
are a completely different story when it comes to engine oil, and that
Redline straight weight racing oil, for example, is not recommended to
be left sitting in any engine for any amount of time.

bs
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