About
Aircraft Turbine Engine Oils
There
seems to be a lot of confusion regarding authorized oils for
various turbine engines.
After conducting quite extensive research on the topic, I
decided to condense my notes and post it online to share with
others.
The
first rule is; always refer to the Maintenance Manual. Authorized
lubricants are clearly listed. If the primary is not available,
use an alternate.
There are two basic types of aviation gas turbine "Mil Spec" oils (specially formulated to meet strict military
standards);
MIL-PRF-7808
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MIL-PRF-23699
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Lubricating oil, synthetic
base, for aircraft turbine engines. Formerly
designated as MIL-L-7808
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Lubricating oil, synthetic
base, for aircraft turbine engines. |
Operating lubricating oil for aircraft turbine engines, helicopter transmissions and accessory equipment. |
Operating lubricating oil for aircraft turbine engines, helicopter transmissions and accessory equipment. |
Designed
for low temperature environments (such as Arctic,
Antarctic, and high altitude operations), their
viscosity allows for cold starting down to -51C.
Used by the US Air Force as well as many foreign
militaries.
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More
widely used and allow cold weather starts down
to -40C. Used by the US Navy, US Army, US Coast
Guard as well as many foreign services. |
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One advantage to using "Mil
Spec" oils in your gas turbine is the ability to
'mix brands'. I usually stay with one brand oil, but in the
case of 'Mil Spec' oils, any brand is the same as the other
(with the same Mil Spec number).
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The
formulations between 'Mil Spec' oils and commercial
oils are very similar. In fact, the 'Mil Spec' number
can easily be cross referenced to it's commercial 'brand
name' and type counterpart. Commercial oils must have
approval of the engine manufacturer to be used in each
engine model through an extensive bench and flight testing
evaluation process that costs millions and can take
up to ten years to complete. This is why there are only
three major producers of turbine oil; Air BP (was Exxon),
ExxonMobil (was Mobil), and Shell.
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Although my gas turbine Maintenance Manual does not direct
flushing the lube oil system when switching from MIL-L-7808
to MIL-L-23699 or back, it is not advisable to mix these types
of oil. Just pick one Mil Spec type and stick with it.
Do
not use gas turbine oils in any internal combustion engine!
There is very little similarity between this gas turbine application
and the lubrication requirements of a typical internal combustion
engine. Jet turbine oils aren't exposed to the byproducts
of combustion. They are primarily designed for excellent,
extreme temp viscometric performance with thermal and oxidative
stability. Gas turbines have no blow-by and virtually no highly
loaded areas. Gas turbine oils are very thin, have no detergents
or dispersants, and act more like a coolant than a lubricant.
T58
Turbine Engine Fuel and Lube Oil Requirements
In
accordance with the Fuels
for USAF Manual, most military turbine engines will run
on almost any 'Kerosene based' Dinosaur
fuel including; Kerosene, JP-8, JP-5, JET A, or JET A1.
Diesel is also acceptable although you should mix it with
about 25% gasoline to reduce the smoke. I set my Fuel Control
to "JP-5" so I can use either Kerosene or JP-5 without
further adjustments. Complete Fuel Specifications and Standards
are online at the International
Association for Stability, Handling, and Use of Liquid Fuels.
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My
T58-GE-3 Maintenance Manual NAVWEPS 02B-105AHB-2/T.O.
directs the use of MIL-L-23699 synthetic lube oil in
this motor. I use Mobil Jet Oil II since it meets MIL-PRF-23699
specifications (which superseded MIL-L-23699) and is
approved by General Electric for use in all their turbine
engines.
The
latest approved Turbine Oil MIL-L-23699E
contains improved corrosion inhibitors and is recommended
to replace MIL-L-23699 as stocks are depleted. Also
available under NSN 9150-00-985-7099.
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Rolls
Royce Gnome Turbine Engine Fuel and Lube Oil Requirements
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