Tom Barber

There have been two or three posts recently about switching to heavier oil in the summer. It is probably okay to go to a heavier weight for the winter rating, i.e., the smaller number that precedes the W. However, it is not a good idea to do this for the summer number. One posting offered the theory that it is okay to go to a wider range than the manufacturer spec'd, i.e., from 10W-40, to 5W-50. This simply isn't true. the reason is simply that it isn't a good idea to run a heavier oil in the summer than the manufacturer recommends. You just simply can't say that "It is summer, therefore use a heavier oil than the manufacturer recommends." If that were true, then why not put axle grease in it? The oil has to flow through very tiny passages in the block, through openings in the crank bearings and into the crank, etc. The viscosity of oil that the manufacturer recommends is a viscosity that has been tested by the manufacturer and it's ability to flow as required has been verified.

Follow the manufacturer's recommendation, and you are very unlikely to have a problem, but if you do, then at least you haven't invalidated your warranty through improper maintenance.

Tom Barber

winder

higher viscosity oil doesn't equal better lubrication.
that IS what you want: consistent lubrication.

with modern oils, and especially synthetic lubricants, viscosity is better maintained through the range of the oil temperatures in a motor. internal engine temps don't vary that much with outside air temps. (winter to summer)
if the cooling system is good, it shouldn't vary that much either. it just takes longer to get full engine heat because the radiator, or oil cooler for that matter, draws more heat off if outside air temp is low.
with higher reving engines, faster reciprocating parts can move through the oil. they can tend to "aireate" the oil. that is; that air bubbles get swept through volumes of oil. higher viscosity fluids tend to hold those air bubbles. that can create "dry" spots as the oil and air bubbles move through oil pumps and tiny galleys to bearings.
i build and race on VERY high rev motorcycle engines (15,000RPM+). i NEVER use an oil over 10W30 in bike motors. some guys use straight rate synthetic of 10W or 15W! and have never seen any oil or premature engine wear, due to bad lubrication.
on tear down, the motors are clean, no oil soot or "hot spots" indicated on friction surfaces.

turbo engines have a wide range of temps that oil has to move accross. from cumbustion areas on top of the head, and bottom of the pistons (~1500F+)to turbo bearings (~1700F) to crank and cam bearings bearings(~600-700F), to even return galleys and oil coolers(~500F). (these #'s are rough estimates. they can be higher or lower on any engine. i don't know what the 2.7T #'s are.)
stay with a hi-quality petroleum. or synthetic as recommended by the owners manual.
w

Tom Barber

as James Bartyles.