Posted by Jim Chance on December 20, 1997 at 12:11:23:
In Reply to: Re: synthetic oil posted by Jim Ferguson on December 18, 1997 at 22:52:49:
I have little experience with synthetics,
but did run an oil monitoring program for
60 diesel engines for about 10 years.
Basically what I found was that low grade
mineral oils, grade "cc" and lower, had
poor viscosity stability as it got older
and a strong tendency to oxidize. Oil
grades "CD" and higher never failed but
did become contamenated with carbon from
blowby, fuel, dirt, wear particles, coolant
and so on. Wear particles and coolant were
always due to mechanical failure. Fuel
dilution was usually due to mechanical failure
but could result from excese idling. Air
filter problems were responsible for most
dirt in the oil. A by pass filter in
addition to the standard full flow made solids
contamination a non issue, but did not help for
fuel dilution.
The thing that was most surprising, but
perfectly reasonable in retrospect, was
that engines that leaked or burnt alot
of oil never needed their oil changed,
because we changed it "a gallon at a time".
What we finally settled on was full flow
and bypass filters, CD class mineral oil,
oil analysis every 250 hrs, and oil change
every 750 hours. We never had any lube
related failures.
We looked at synthetic oils, but decided they
offered no benifits due to the excellent
perfomance of mineral oils.
With a small engine like a PW, it is cheaper
to change the oil then test it. Unless one
was willing to invest in testing and filtration,
you would probably get equal protection for less
dollars using a high grade mineral oil and
frequent changes.