atlasair
Posts: 99
Joined: Sat Jun 05, 1999 11:43 pm

Mixing Oils

Wed Jun 06, 2001 1:00 am

hi
Lets say you have an engine that has sticker that says MOBIL JET II.Question is can you add an oil from another conpany, say Chevron or 2380?

AtlasAir
 
Buff
Posts: 1066
Joined: Fri Mar 16, 2007 1:29 pm

RE: Mixing Oils

Wed Jun 06, 2001 1:16 am

My recall (as a pilot) was that with Turbine oils it was best not to mix manufacturer types, but not forbidden. As long as the MIL Spec was identical, in a pinch it was OK to mix.

Recip oil types were restricted to detergent/non-detergent based oils of the same viscosity. Don't mix "W" oils with non-W; only use non-W when breaking in a new engine; multi-viscosity oils generally not approved.

An engineer's perspective would be more legit than my humble recollections, of course!

Best Regards,

Buff
 
JT-8D
Posts: 423
Joined: Sun Dec 31, 2000 11:34 pm

RE: Mixing Oils

Wed Jun 06, 2001 1:28 am

As a rule, on jet engines, dont mix. We switched from Exxon 2380 to mobil 254 many years ago. The oils were supposed to be compatable. After numerous filter clog lights, and delayed departures, it was found that the oils where not compatible. Little black balls where found in the oils strainers. When the procedure came out to drain out the old oil, then refill with new, there was so many of these ball things in the oil tank that when we removed the drain plug, the oil wouldnt come out. Had to poke a screwdriver into the hole to get it to drain. As buff said, you would expect oils to be compatible if they are the same mil-spec, but I guess not..JT
 
gt1
Posts: 124
Joined: Wed Feb 21, 2001 10:30 am

RE: Mixing Oils

Wed Jun 06, 2001 1:54 pm

I would suggest that mixing oils in a turbine engine is not a big deal. In fact, sometimes it is the recommended procedure. The currently accepted method of oil type change-over is the top-off method, which means you simply add the new type of oil to the old oil. Eventually, you end up with a oil system completly full of the new type of oil. Complete change-overs are not recommended because they spike the additive package which causes plugged oil filters. The "little black balls" were bits of debris left by the old oil, and dislodged by the detergents in the new oil. 2380 allways left some carbon in the oil system. 254 is a more detergent oil, so when it is added to 2380, it will cause some filter clog lites to come on. The new oils, Exxon 2197, and Mobil 291 promise to be the best turbine oils yet, but they have a strong detergent package in them, which when added to an old oil system, will be bound to plug some filters, but that is only because they are cleaning a dirty oil system, not because they are incompatable with the old oil.

On the other hand, Sundstand warrenties their IDG's based on oil brand/type. So mixing of oils there should not be taken as lightly.

Please check your companys procedures on this issue. It makes for some interesting reading.

gt1
 
T prop
Posts: 910
Joined: Tue Apr 03, 2001 4:33 pm

RE: Mixing Oils

Wed Jun 06, 2001 2:52 pm

On PW100's, we are cautioned in the Pratt maint. manual not to mix different brands or types since the chemical structure may make them incompatible.

We are also required to service the prop hub with the same type of oil that's in the engine. We use BP (Exxon) 2380 now, if we wanted to switch to Mobil or some other type, Pratt requires us to drain and flush the engine oil system.

T prop.
 
TimT
Posts: 168
Joined: Sun Jun 03, 2001 1:38 pm

RE: Mixing Oils

Wed Jun 06, 2001 4:32 pm

The company I work for just changed from Exxon 2380 to Mobil 291. We changed the stickers as far as I know. There was a lot of dealing with engineering about compatibility in CSD/IDG, starter, and generators, but the final bulletin allows mixing.
 
JT-8D
Posts: 423
Joined: Sun Dec 31, 2000 11:34 pm

RE: Mixing Oils

Thu Jun 07, 2001 2:12 am

GT1 has a good point. We tried the topoff method, and we got the "carbon balls". Thats when we started draining and refilling. Maybe it was just to get rid of the residual? For some reason, half our fleet still uses 2380 in the csds, and all our idgs use 2380 also. Apus seem to be split too. 757 uses 2380, 737 uses 254. Does this make any sence?..JT
 
atlasair
Posts: 99
Joined: Sat Jun 05, 1999 11:43 pm

RE: Mixing Oils

Thu Jun 07, 2001 5:25 am

JT-8D what fleet are you talking about?
 
JT-8D
Posts: 423
Joined: Sun Dec 31, 2000 11:34 pm

RE: Mixing Oils

Fri Jun 08, 2001 1:01 am

My companies airplanes is what I mean by fleet..JT

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