Re: Oils

[George Graves <gmgraves@domain.elided>]

On Tuesday, March 4, 2003, at 03:10 AM, Brian Shorey wrote:

> <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).
Nothing per se, they're two different subjects. HOWEVER, they are 
somewhat tied together because multi-viscosity oil, being designed for 
more modern engines, has the more aggressive additive package. As far 
as viscosity is concerned, modern engines have much tighter tolerances 
and smaller bearing gaps in the bearing journals, apparently, than do 
older engines. This means that less oil pressure is required to support 
the crank and rods in their journals. That's why modern engines can use 
oils with viscosities 10W-X, 5W-X, and even 0W-X (where X is the warm 
engine viscosity such as 30, 40, 50 or 60W).


> 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).
That is not clearly the case. Maybe if I explain how multi-viscosity 
oil works, it will paint a clearer picture. Multi-vis oils contain, as 
you say, a viscosity modifier. This modifier consists of what amounts 
to billions of little, sub-microscopic, polymer "coil springs"  added 
to the oil. When the oil is cold, these little "springs" coil up tight 
reducing their overall volume and making the oil thinner. As the oil 
warms, the "springs" uncoil, making the oil more viscous. An analogy 
would be flour added to water. Water is very thin, pours and runs 
easily. Add flour to the water, and as the individual flour granules 
absorb the water, the mixture thickens, it does this because the flour 
granules expand as they absorb the water. Now, if we could come up with 
a flour that was temperature sensitive, I.E. it gave the water up when 
it got cold, and re-absorbed it when it was warm, we would have a 
perfect analogy to multi-weight oil. Therefore, I'd say that the basic 
oil, before the viscosity modifiers are added, would have be very thin. 
Probably even thinner than the final cold weight of the oil because 
even coiled-up, these polymer "springs" add volume to the oil.

> 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.
It depends on the manufacturer. Some oil manufacturers put a similar 
additive package to all their oils, while others use less aggressive 
additive packages to their single-weight oils because they realize that 
these oils will be used in older cars, motorcycles, lawn mowers, and 
other low-tolerance engines. Some companies, like Castrol, for 
instance, make single-weight oils specifically designed for classic 
automobiles employing oil filters. These oils have a different type of 
additive package, one which contains anti-rust compounds, anti-wear 
ingredients and viscosity index modifiers to stop the oil from thinning 
too much as it gets hot. All of these are combined with detergents and 
dispersants which are much less aggressive than those of a modern 
counterpart. For even older cars, those made pre-war for example, and 
made without oil filters (as many were), there are other special oil 
formulations which have the anti-rust compounds, anti-wear ingredients 
and viscosity index modifiers, but omit the detergents and dispersants 
altogether, or use very little of either.


> 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.
They probably leak too, or suffer from premature main seal failures and 
possibly premature bearing problems, and the owners just chalk it up to 
the mythology about Italian cars- that they leak like sieves and are 
high maintenance. They might not even realize that if they used the 
correct oil, the leaking might stop, or at least abate somewhat and 
that their main seals would last several times longer and they could go 
100,000 miles between bottom-end rebuilds instead of 50,000. The oil 
companies say that engines not designed for multi-weight oil will 
suffer from low oil- pressure and poor bearing support when they are 
cold leading to premature main and rod bearing failure.

Please understand, I'm not a mechanic, or an expert in this field by 
any stretch of the imagination.  I'm just going by what I've read in my 
research on motor lubrication for the article I'm writing and passing 
it along to Digest readers for what it's worth. These are the 
recommendations of the companies which manufacture these lubricants. 
Perhaps they err too much on the side of caution for liability's sake, 
and in practice, the consequences of using these modern lubricants in 
older cars are not nearly so grim as they predict. I would have no way 
of knowing. And asking mechanics is also an empty procedure. Ask a 
dozen Alfa mechanics and you'll get at least two dozen answers. People 
tend to recommend what works well for them.  The long-term effects of 
using the wrong oil are just that, long term effects. Usually, when 
something does happen, its so far removed from the event, that 
pathological correlations are rarely made. How, for instance, is one to 
know for sure that a different oil would have made their engine last 
twice as long as it did? One has to rely on someone's data here, and 
the oil companies are the only ones that *I* know of who have done the 
research and that's probably at least a little tainted by commercial 
needs.


> 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.
Well, I mentioned Redline as a source for information, not as a 
recommended oil . They probably have more literature available on the 
various aspects of automobile lubrication than does any other company.



> bs
George Graves
'86 GTV-6
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