Viscosity and Wear

[buster]

If Jet/Turbine engines run at 38,000 Rpms and use a 5 weight oil and the Stever Bergin article suggests viscosity has nothing to do with wear, 20wt oils should be of little concern. I realize the jury is still out on this, but I think many people are stuck in the old world thiking which is that a heavier oil must mean it's better. Any thoughts?

 

[yannis]

quote:

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Originally posted by buster:
If Jet/Turbine engines run at 38,000 Rpms and use a 5 weight oil and the Stever Bergin article suggests viscosity has nothing to do with wear, 20wt oils should be of little concern. I realize the jury is still out on this, but I think many people are stuck in the old world thiking which is that a heavier oil must mean it's better. Any thoughts?

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I think it depends on the temperature and the manifacturer specifications.
For temp over 86F i would prefer a havier oil.

 

[buster]

What cought my attention is that Jet engines use a 5 weight oil and run at 38,000 rpms. Obviously car engines are much different but I thought it was interesting. Thanks George!

 

[BOBISTHEOILGUY]

Remember when talking jet engines, these are not recip's, they do not introduce blow by gases, they do not put any extreme pressure on the bearings due to excessive pressure as they just spin on an axis, like a fan blade, where a piston pushes against cranks, valves against cams all of which is not existant in a jet engine, there fore shearing isn't as extreme. Temps on the other hand is a different story between jets and automotive engines.

 

[buster]

Thanks Bob, I figured there was much more to it.

 

[yannis]

i had a similar question and asked valvoline europe ,why the usa cars run mostly on 10W30 in
contrast with what is common in europe.The answer:
Dear Mr._______,
Thank you for your E-mail.
The American engines are build in such a way
that there will be less stress on the oil than in
European engines.
They have big slow running engines, and we
have small fast running engines.
Further more, they drive slower than we and
they drive long straight roads, and we are
constantly driving in cities etc.
Still the latest European engines also drive
on thinner oils, like 5W-30 or 0W-30.
This is possible because nowadays we are
using synthetic base oils and better additive
systems.
Further more, the latest engine f.i. of Volkswagen
are build in such a way that they can handle thin
oils.
From field practice, I have noticed that these new
engines with their thin oils are consuming a lot of
oil. (VW allows 1litre on 1000 km.)
Another thing is that many of these viscosities are
just a commercial thing and are technically spoken
not necessary.
Hope this helps a little.
Kind regards,
Arie de Graaf
Valvoline Europe

 

[Ken2]

In addition to what Bob said, if the bearings are made bigger, the "per-square-inch" load on the bearings is reduced, so there's less pressure on the oil. Smaller clearances, lighter bearing load, and everything Bob said, all make for a very different situation in a turbine than in a reciprocating engine.


Ken

 

[tom slick]

what website is telling you that says "jet" engines run at 38,000 rpm?
it's true that some "turbine" engines run as fast as 65,000 rpm, but those are not "jet" engines, they are small auxillary power units. (ever wonder how they start a jet engine?)
a true "jet" engine runs anywhere from 12,000 to 16,000 rpm depending on the model. they only have precision ($$$$) roller and ball bearings inside of them. there is not much friction and it is impossible for combusiton gases to come in contact with them. they only get their oil changed about every 2 years. for the most part the oil is a coolant for the hot parts.

 

[BOBISTHEOILGUY]

Thanks Tom Slick. Glad to know I havent forgotten all of my basic jet engine mechanics I learned back in the 70's.

 

[JohnBrowning]

Anotherthing alot of people fail to reliase is that the altitude were juets funtion ( usualy above 24,000 Feet) all air temps are negative. The oil has to flow through a HOT engine while exposed to some nasty temps.

 

[tom slick]

no problem, i've been a jet engine mechanic in the air force/air national guard for 9 years. if you guys have any other questions about jets let me know.
one thing that is interesting is that on the current engines i work on we do not do UOAs, which are called JOAP in the air force.