John,
Oil is splashed or pumped round the engine for lubrication. Two of the
obvious places for oil are the cylinder head and the bores. When the engine
is new and all of the components fit properly there is very little oil lost.
When there is a bit of wear the oil loss starts. When the piston rings and
the cylinder bore have worn a bit then some oil can get past the rings up to
the combustion chamber and it will burn off, so will any oil trickling down
valve guides that are worn. This burnt oil manifests itself as blue exhaust
smoke and is not a concern unless there is lots of it. As a point of
interest, years ago some engines were designed to use oil, the old 3.5L
rovers would use a pint in 150 miles.
You cannot 'correct' or reduce oil consumption without major engine
work, re-boring the cylinders and fitting new rings or getting the valves,
guides and seats re-done. This is expensive and usually not worth it for
just oil consumption.
Mineral ver. synthetic should react in the same way, unless synthetic
is less prone to burning off, I am not sure about this.
Changing the viscosity will have little effect as the oils are all
fairly thin at the temperature that they operate at. While on the subject of
viscosity let me expel a myth. The theory is that putting a thicker oil in
gives you a better oil pressure, this is true, the myth is that this is
better for the engine. A thicker oil needs more pumping as it is harder to
push round, resulting in higher pressure. A thinner oil is easy to move
round so it gets to your engine but will give less pressure. The best bet is
to stick with maufacturers spec.
There is no average oil use, I do not know if mine uses any, if it does
it is a very small amount as I never notice it.
Oil burns off in the combustion chamber. The oil does not go anywhere
to cool the engine, cooling is purely incidental to the oil being pumped
round for the lubrication cycle. Oil coolers on both engine oil and
transmission fluid are there to keep the oil cool for lubrication, not to
cool components. Coolant is pumped round purely to cool the engine. Smaller
auto. tranmissions do not need coolers as they do not reach the higher
temps. that the cruiser seems to suffer from.
Regards,
Clive Marks
Home: +44 1293 514600
Mobile: +44 7821 491897
Crawley, West Sussex, UK.