At Deere Rotary, we tried turbine oil for the metering oil in a short test.
The seal wear was fine, but the engine was surprisingly dirty. Could have
been overoiling the engine. We deliberately did not use the oil for the
bearings mainly because the viscosity is all wrong. I am quite sure the film
thickness will be inadequate leading to high wear and more importantly
possibly catastrophic fatigue of the bearing material. The role of antiwear
additives in conventional oils is not well understood in terms of the
rotary's needs. There may be long term wear issues with side housings.
I think it will be an interesting test, but I'm not too optimistic about the
outcome.
Jon Lauter
Rotary Power Marine Corporation
www.rotarymarine.com
I don't plan on using it for the seals and that includes the side
seals as two cycle oil is proven for that. No telling what turbine oil
does when mixed with gasoline.
I am mainly interested in its anti coking properties.
As long as it does the bearing lube job at typical oil temps of 210 F
I'll be happy.
They have made some changes since then Jon. Robin just brought home
some Exxon 2197. It pours at room temp about the same as Mobil 1
15W 40. Can't say what the viscosity of either one is at 210 F.
Turbine oil could be higher. I do know we don't need the sliding
wear additives in motor oil designed for cam shafts.
Paul Lamar
The concept of viscosity as a function of engine protection should not be confused
with the property of the oil to resist metal to metal contact, which is shear
strength. All oil serves three functions: Protects from metal to metal, Absorbs
heat (cools) until it reaches it's own breakdown temperature, and cleans metal
parts it contacts from any contaminant thereon.
Before synthetics you had better run 40 or 50 Weight viscosity in a heavy duty
application (racing - Paul?, or towing), to obtain the best shear strength that was
possible at that time at elevated temperatures.
Synthetics make it a whole new ball game as shear strength (of the worst synthetic)
is typically 8 times what the best shear strength of a petroleum product is. Thus
you are seeing "equivalent" weight ratings on synthetics so the public will buy
them (using their old way of thinking). Lately, however Mobil has released 0
(Zero) weight synthetic as their latest and greatest product, so maybe they are
starting to educate the consumer?
An "additive package" of various substances goes into both types of oil, for
specific purposes i.e. high pressure applications (camshaft), anti foaming, etc. A
lot less of this stuff is needed in a synthetic as they are more naturally so, but
each still has additives. This is as good an argument for changing oil as I have
ever heard of, as the "additive package" is bound to lose it's effectiveness over
time and revert to the properties of the "base stock" which is all that is left.
Petroleum, due to the wide varieties of molecular hydrocarbon chains therein, has
some chains that are shorter, lighter, and more volatile (sooner out the breather),
and other longer chained molecules that have an affinity to joining still other
longer chains. If this did not occur, oil would not protect your engine, but this
process if it keeps occurring long enough after having lost it's additive package,
becomes sludge.
Synthetics benefit by having shorter, specifically tailored molecular "base stock",
where every molecule is identical! (Except additive package) ... by having this
'homogenization" of atomic centers of adjoining molecules at uniform distances,
they have a very strong attraction for each other (which causes high and low temp
stability).
Seal compatibility of synthetics has always been their "achilles heel". I like
Paul's oven heating and seal soaking approach! Just the facts, Mam ... All
turbine oils are synthetic, but not all synthetics are turbine oils. Turbine oils
typically do NOT get contaminated by blowby and are as clean (appearing) when they
are drained as when they are new. Reciprocating engine synthetics (destined to
contamination) are still evolving (Mobil Aviation Synthetic?), so we might as well
resign ourselves to being the "test pilots" of rotary synthetic lubricants.
Synthetic gear lubes, greases, etc. have already proven themselves superior in most
applications (except cost competitiveness).
Aviation Consumer Magazine which is about the only flying magazine I truly respect
as they do NOT accept freebies and then write about them, had an article a few
years back that put a lot of oils "to the test" ... they used a rotating cup
containing 4 steel ball bearings lubed only by the test oil. An arbor press
squashed the balls together until the oil failed to lubricate them and they galled
... the pressure needed was noted. If I remember correctly, seems the clear winner
of the test was a product called Bel-Ray (synthetic).
If this stuff is still available, I would like to nominate it for Paul's testing.
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