Understanding Model Jet Engines
Design, Fuel & Lubrication 

Mobil 254 Jet Engine Oil

You must add a little bit of turbine lubrication oil such as Mobil 254, Mobil Jet II Oil, BP 2380, AeroShell 500, etc. to your Jet A, kerosene or diesel.

This oil is used to lubricate those little ceramic bearings on the turbine shaft that are spinning at warp speed and perhaps the second stage turbine bearing if you are running a two stage helicopter or turbo-prop engine. 

Yep, oil choice is very important if you want your model jet engine to last.

Problem is, synthetic aviation jet oil contains some pretty nasty chemicals. 

One of the most toxic among these is Tricresyl Phosphate (TCP); a chemical that causes peripheral neuropathy (nervous system damage). TCP is used in turbine oil as an anti-wear additive and while the concentrations are low at about 1-5% by weight in most aviation turbine oils, further diluted by your fuel to oil mix ratio, it's still very bad stuff.

Toxicity is of course dose and exposure dependent and it's not like we have our noses up the tail pipe the entire flight, but one has to consider long term effects; not to mention the fact it was never intended to be part of the combustion process in model jet engines. 

Moreover, very little of the fuel oil mixture is actually diverted to the bearings for lubrication and cooling; so in effect, you are burning the vast majority of this toxic oil (along with your money) that isn't even being used for lubrication purposes.

Speaking of burning your money; Mobil Jet II, 254 and other aviation turbine oil is also getting bloody expensive and can be hard to find considering it's certainly not intended for the general public to be using. Up here in Canada we are shelling out about $40 for a quart (I get/got it from our local helicopter base which sells the stuff).

I'm not saying Mobil 254 or the others are not good model jet engine lubrication oils (I used 254 exclusively for a good number of years), but most model turbine engine manufacturers now agree it and other brands of aviation jet oil toxicity dangers largely outweigh their good high temperature, anti-oxidation bearing lubrication properties. 

Some manufactures for example now recommend using a good quality 2-cycle oil; which after all has been designed to be burnt with limited toxicity. Keeping in mind, no atomized oil in a combustion process is safe to breath, 2-cycle or otherwise.

Problem with 2-cycle oil is some (certainly not all), can oxidize under the high heat, varnishing up the turbine bearing and/or gum up the bearing pre-load tube causing premature bearing failure. It can even gum up and block the fuel tubes in the combustor. In other words, only use a 2-cycle oil if your specific turbine manufacturer recommends it. If they do, use the exact brand/type they recommend.

Those that do authorize use of a 2-cycle oil, will generally recommend conventional based oil and not synthetic. Reason being is some synthetic 2-cycle oils don't mix well with Jet-A, kerosene or diesel and will settle out.

An easy way to test that is to mix some 2-stroke oil (or any lubricating oil) with your fuel of choice, put it in clear glass jar and let it sit on a window ledge for several weeks. If the oil doesn't separate from the fuel, you'll know for sure it won't settle out. 

This is actually a good test for any new oil you decide to mix with your Jet-A, kerosene or diesel fuel to ensure the oil won't settle out. 

Mobil DTE 24 (also an ISO 32 grade hydraulic oil) can be used and it's generally easier to find, and in smaller 1gal / 4L jugs. I've used DTE 24 once when I couldn't get any DTE Light, and it seemed to work just as well as DTE Light.

I'M SO CONFUSED!

If you're scratching your head about what jet oil to use in your model turbine engine, you're certainly not alone.

Best recommendation is to check & confirm with your engine manufacturer and use what oil/s they recommend or perhaps what others at your flying club are using with good results if they run the same engine/s. Keeping in mind some model turbine engine manufacturers won't honor any warranty they may have unless you use their oil recommendations! 

The main problem is there really is no lubricant that has been specifically formulated for model jet engines. For years now, the entire model turbine engine industry has basically been using whatever available oils seem to work the best with as few compromises as possible. This is changing however with the continued growth and popularity of these small model turbine engines.