Salutations:

Actually the difference is this. Except for last summer - most of England
and Europe is on average 5-10 degrees cooler than most populated parts of
North America and there in is one of the problems with mileage or time
based oil change schedules. I maintain that the correct answer is to
acquire an accurate set of oil and transmission gauges and pay occasional
attention to them as you go.

Granted - for the most part oil thins and/or carries particulate more in
step with engine condition and tune than driving style. However in terms
defining a wise 3/6 month or thousand mile interval - attributable oil
degradation is importantly related to environmental conditions in which
your respective car operates seasonally.

For example - you run a high mileage engine in Europe where it is often
damp and not so warm. Your oil thins at a greater rate than certain north
American SAAB brothers or sisters because of hydroscopic action in the
block and fuel blow by through the seals and rings on cold starts. Thin
your juice enough and eventually the baby burps a bearing one cold morning.

For our American cousins in Texas, where the average ground temperature is
much higher and air much dryer, oils tend to revert to a more granular
state over time - which more readily presents the possibly of catastrophic
failure under load and heat. There is more ongoing evaporation of unspent
fuels and water vapor in the block - but they face the problem of
concentrating carbon levels as the oil itself evaporates with the vapor
and unspent fuel.

Fine carbon in an increasingly fuel and humidity rich environment acts as
a bit of a lubricant - but viscosity is thinning at lower temperatures and
pressures. Almost the opposite is the case in a dry, high temp environment
where viscosity is increasing at lower temperatures as more concentrated
carbon crystal is in movement across your bearing faces. Both oils behave
much the same way at temperature, but both wearing the engine differently
as the clock ticks over.

Brother Grunff's '86 T16 looks the way it does under the cam cover because
it is changed as indicated by the actual condition of the oil, no doubt
careful attention to warm up at start and a generally good 'Carma'(tm) for
helping out so many folks on this NG. For him, the semi-syth makes sense
because he is more likely to pass it through the main seal as he will be
thinning his oil more quickly than brother Fred.

However - brother Fred isn't thinning out as quickly as brother Grunff and
his seals are more likely swelling than cracking - his greater concern is
the potential for surface failure in the block. Synthetic is *very* good
at holding it's set viscosity into extremely high temperatures - but no
better at keeping larger carbon crystals from forming in the fluid or
handling evaporation demands as dictated by the condition of his engine.

Anyway, as I mentioned earlier - I'm getting my '89 block prepared and I
am searching carefully for a really accurate set of gauges for oil
pressure as well as transmission and oil temperatures. I'm also fitting an
engine hour clock under the hood when it finds a home.

Much is often made of the social 'effects' of marketing and my take is
that much of the wisdom related to automobiles is misplaced. Horsepower
isn't really as important to most folks as Torque - mileage can be
important when you are discussing chassis issues, but engines and
electrics are related to how many hours, in what conditions and how
closely the maintenance is adhered too.

Lubricants and cooling fluids, natural or otherwise, are entirely subject
to application. Thusly - I still think the best hope anyone has of getting
it right is to have realtime monitoring in place. If there is any
improvement that I would like to see focused on myself - it would not be
in new oils - but in more effective filter, breather and monitoring
technology.

Sorry for the great length - pet subject of mine..

Hence my smiley too! :)