In a message dated 8/21/02 1:13:19 AM, jbrush@AROS.NET writes:

>You lost me there. Doesn't that mean that multi weight is better and that
>straight weight is more of a strain on the engine when its 'cooler' than
>the rated temp for that weight?

There are different oils for different purposes, and multi-viscosity serves
SOME of the needs of automobiles. However, note that there are different oils
for GAS versus DIESEL engines, and transmissions versus motors.  If oil was a
one fit for all, you could put 10w30 in your wasserboxer.

The purpose of oil is cool your engine. Lubrication is one way this happens.
A lighter weight oil doesn't carry away as much heat as a heavier weight oil.
The lighter weight oil will also tend to "boil" off over time, more easily
than the heavier weight oil. Multi-viscosity oils are blended/constructed to
mitigate this (and synthetics are better than dino in this regard), but they
don't really get rid of it entirely.

So your engine is in a conundrum. It needs a relatively light weight oil so
that it can turn over without too much resistant due to the oil, but it needs
a heavy enough oil so that it is lubricated and doesn't overheat. 30 weight
(in most climates) is good enough for this in the VW horizontally opposed
engines. It's what they had when the engine was designed. It's what the
tolerances allow.

Later engines have closer tolerances and need something a bit thinner for
lubrication, but still need that heat carrying capacity. That's how the
multi-viscosity oils got developed.

The wasserboxer, being a bit of hybrid, can use the 30 weight (especially in
hotter climates), but 20w50 is preferred. 10w30 is too thin for most
temperate climates and will cause your oil pressure switch to activate as the
viscosity (thickness) at tempatures becomes too thin to adequately lubricate
(and hence cool) your engine.

Does that clear it up for you?