Mixing oil grades?
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Mixing oil grades?
Morning all, anyone know if it's a bad idea to mix grades? Specifically W100 with straight oil. The engine in question is an M14-P (Yak 52) and I have absolutely loads of the straight stuff left over from running in after overhaul. I am sure it is a no-no but could anyone explain why?
Ta, S-S
Ta, S-S
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Not so long ago I was talking with several oil companies about changing from a mineral oil to semi synthetic.
Apparently by law all aero oils have to be compatible with one another, I imagine it would make more sense to use the same oil, but there should be no technical reason why you cannot change from one to another
P...
Apparently by law all aero oils have to be compatible with one another, I imagine it would make more sense to use the same oil, but there should be no technical reason why you cannot change from one to another
P...
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Here's the opinion of the oil company.
No problem with mixing, oil grades, as Potter1 says, it's part of the specification requirement that the oils should be compatible with one another.
The only issue is when you have used straight oils for an extended period (3-400 hours) as this type of oil does not contain any deregents; unlike the "W" type oils.
Extended running on straight oils tends to result in carbon deposis forming on the engine internals - particularly the casings. With "W" oils these particlese are kept separated by the dispersant additive, carried by the oil in suspension, and removed by the filter.
If a "W" type oil is used once a significant amount of deposits have been allowed to build up, then the dispersant additives can have a detergent action; encouraging the carbon deposits to be loosened. This can then be a problem with filter blockage, or even obstruction of an oil gallery if the filter is inefficient, or bypassed through blockage.
The other point to make about straight oils is that they do not contain any additives, so no anti oxidant etc. This means that straight oils tend to degrade more rapidly than "W" oils, and so have a shorter fluid life. This means that it is a good idea to drain them reasonably frequently, but with an M-14 you should be changing every 25 hours anyway (you only have screen filters, not a cartridge), so 25 hours shouldn't be too much of a concern.
In short, no problem in using up the straight oil, but if you have masses of the stuff and go beyond 300 hours on straight, be careful when changing back to "W" oils. This would mean checking the filters (scavenge and inlet) more frequently in the first 50 - 100 hours after changing back to the "W" oil to ensure that they are not blocking.
If you have less than 300 hours supply of straight oil, then use it up without another thought.
Rob Midgley (Shell Aviation Technical Manager)
No problem with mixing, oil grades, as Potter1 says, it's part of the specification requirement that the oils should be compatible with one another.
The only issue is when you have used straight oils for an extended period (3-400 hours) as this type of oil does not contain any deregents; unlike the "W" type oils.
Extended running on straight oils tends to result in carbon deposis forming on the engine internals - particularly the casings. With "W" oils these particlese are kept separated by the dispersant additive, carried by the oil in suspension, and removed by the filter.
If a "W" type oil is used once a significant amount of deposits have been allowed to build up, then the dispersant additives can have a detergent action; encouraging the carbon deposits to be loosened. This can then be a problem with filter blockage, or even obstruction of an oil gallery if the filter is inefficient, or bypassed through blockage.
The other point to make about straight oils is that they do not contain any additives, so no anti oxidant etc. This means that straight oils tend to degrade more rapidly than "W" oils, and so have a shorter fluid life. This means that it is a good idea to drain them reasonably frequently, but with an M-14 you should be changing every 25 hours anyway (you only have screen filters, not a cartridge), so 25 hours shouldn't be too much of a concern.
In short, no problem in using up the straight oil, but if you have masses of the stuff and go beyond 300 hours on straight, be careful when changing back to "W" oils. This would mean checking the filters (scavenge and inlet) more frequently in the first 50 - 100 hours after changing back to the "W" oil to ensure that they are not blocking.
If you have less than 300 hours supply of straight oil, then use it up without another thought.
Rob Midgley (Shell Aviation Technical Manager)
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Straight oil is normaly used when the piston rings are new as it helps the rings and bore "bed in" and is normaly run for the first 50 hours OR untill the oil consumption drops and maintains a normal level.
W oils are genraly held to be better lubricants so mixing W with straight will cut some of the benifits of the W oil but it is unlikely to do any harm.
Why not sell it back to your engineering company they will be using it every time they change a cylinder !.
W oils are genraly held to be better lubricants so mixing W with straight will cut some of the benifits of the W oil but it is unlikely to do any harm.
Why not sell it back to your engineering company they will be using it every time they change a cylinder !.
