I have seen that on the shelves. Seems rather nonsensical, doesn't it? But
at least the total range is only 20. Claiming a 45-unit viscosity range is
what I found unlikely.
In multi-grade oil, viscosity is extended by adding complex long chain
molecules, which, when folded up, flow easily, to a low viscosity base
stock. When heated, these molecules unfold and simulate the flow
characteristics of a higher viscosity oil.
The problem with this approach is twofold. As the oil ages, these molecules
can break down, at which point the oil only offers the protection of its
base stock (would you run your engine on straight 5W?). Modern oils,
particularly synthetics, are advertising longer and longer change intervals,
so presumably these molecules are fairly long-lived, but still...
Secondly, and more crucially, these oils are designed for modern, tight
tolerance engines, typically with roller rockers or overhead cams. In
situations with loose bearing tolerances, these long chain molecules may not
be large enough to perform their intended function, and will not
successfully simulate a higher viscosity oil. So there you are running 5W
again...
Another consideration is that these low base weight multigrades deliberately
eschew the anti-wear additives that were common in oil formulations at the
time our LBCs were new, in favor of further reducing friction for gas
mileage purposes. A sunburst symbol on the can indicates one of these "low
friction" formulations, which would not be suitable, to my mind, for use in
a mechanical tappet engine.
Personally, I wouldn't use anything with a lower base than 20W50, unless
perhaps in winter in a very cold climate.
In my other vintage engine, a high-performance V8 with much higher valve
spring pressures, I run 30wt "heavy duty". I know some people who run racing
oil, but I don't think that is suitable for typical 2nd-car street use,
involving irregular use and sitting around for long periods, with long time
intervals between changes. It seems obvious to me that racing oil is
designed for short periods of intense use followed by an immediate
changeout. In this context, the concept of "track day oil" is puzzling, to
say the least.
on 7/11/07 10:26 AM, Andrew B. Lundgren at lundgren@byu.net wrote:
> A friend of mine has a new toyota tundra with the 5.7l in it. It takes
> 0w-20. I didn't even know they made a 0...
>
> Max Heim wrote:
>> I've never seen 5W50 before, anywhere. Kind of hard to believe they can
>> effectively stretch the viscosity range that much. I don't think I'd try to
>> use that in a vintage tappet engine.
>>
>>
>> --
>>
>> Max Heim
>> '66 MGB GHN3L76149
>> If you're near Mountain View, CA,
>> it's the primer red one with chrome wires
>>
>>
>>
>
--
Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the primer red one with chrome wires
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