<VV> Synthetic oil

[cmot at ix.netcom.com]

	Regarding how long to leave synthetic oil in an engine I will relate
what I heard years ago when I was flying and doing some personal maintenance
on light aircraft. Mobil came out with a Mobil 1 15W-50 aviation oil for
aircraft engines. Sales points were dramatically improved corrosion
resistance in salt spray tests on engine components. This was beneficial
because so many small aircraft spent most of their lives parked in airports
which were usually in low flatlands. My experience was those areas were many
times prone to fog and or being near bodies of water or rivers. The heating
and cooling daily while parked outside caused the engines to build up
condensation inside and some engines which had the camshafts placed high in
the block would have the oil film eventually run off and the cam would start
to rust. Continental engines were famous for developing bad cams from this
which would wear the lobes down and reduce lift and power. At the time a 6
cyl continental O-300 from say a early Cessna cost $12K for a economy O/H.
	Sales of the Mobil Av-1 oil took off and fantastic performance
increases were reported as well as wear reduction documented with oil
analysis tests. One of the more impressive reports was of loss of all oil
from a ruptured cooler while over mountainous areas with no airport for 50
miles and managing to fly the oil-less engine to an airport without it
seizing.
	My own first experience with a synthetic oil (All Proof 15W-50) back
in the late 70's early 80's in a Sirocco I owned was increased top speed and
15 degree centigrade lower oil temp under the same operating conditions as
regular oil. The lower temp was from reduced friction. Oil consumption in
every case dropped to half of regular premium oil. I later understood the
reduced oil consumption was partly due to the higher flash point of the
synthetic. The oil film on the cylinder wall did not burn off from the
combustion process, maintained lubrication and ring sealing and reduced or
eliminated ring sticking.
Chet
	Back to the aviation oil. Mobil suddenly pulled the product from the
market due to liability concerns. What started to happen was some thought
you could extend your oil changes because the oil was so much better. The
average aircraft engine recommended oil changes at 25 hours. Many were
doubling it or more and not doing oil analysis. The result was a few loss of
power incidents caused by stuck valves. One has to realize that 100 low lead
aviation gas had something like 4 times the lead of the old leaded gas. Many
aircraft engines don't have oil filters, instead having a screen that is
cleaned. The extended oil change caused a increase in the build up of
contaminants in the oil, mainly lead, that eventually caused the valves to
stick. You could actually smell the lead in the oil which would develop a
grey film in the engine from the excess lead. Cure was to stick with the
original 25 change interval but Mobil didn't want to take the chance and
dropped the product in the limited market. So the lawyers and ignorance
killed a great product.
	After my positive experiences with synthetic oils I have continued
to use them in my own vehicles, especially turbo applications which benefit
the most. Cold weather starts are easier. Engine condition later in life is
much better from reduced wear. I have had used vehicles that had sticking
lifter problems that were eliminated as well as overheating. The base stock
of some synthetic brands tended to shrink seals so if you change over a old
tired poorly maintained engine to synthetic expect some oil leaks from the
hard dry seals as the varnish deposits are slowly removed. On newer engines
with better quality seals it did not seem to be an issue.
	I also have some notes I made from years ago of a discussion with an
instructor at a GM Training Center on oil viscosities that I will try to
find that some might find interesting. How my past experience relates to the
latest developments in lubricants I cannot say. I was aware of the zinc
additive issue many years ago and used to dope regular oil with Rislone
which had a zinc package that seemed to cure any deficiencies.