I had a '92 350 in a Burb that went over 350k and the engine was never torn down; compresion in each cylinder was always around 130 psi until I sold it. The only item I had to have replaced was the distributor. Always used a top of the line synthetic such as Amsoil, Mobil 1, rEDLINE, and of course our experimental synthetic fluids.
From the Mobil website:
"Mobil Jet Oil 254 is a third-generation, extra high performance, synthetic aircraft-type gas turbine lubricant engineered to meet the performance requirements for gas turbine engines used in commercial and military aircraft. This product is formulated from a specially prepared, hindered-ester base stock and fortified with a unique chemical additive package. The result is a product having superior thermal and oxidation stability that resists deterioration and deposit formation while maintaining the physical characteristics required by builder and military specifications. The physical properties of Mobil Jet Oil 254 are similar to those currently available, earlier-generation gas turbine lubricants. The effective operating range of the lubricant is between -40°C (-40 °F) and 232°C (450°F).
...Mobil Jet Oil 254 reduces bulk oil oxidation by up to 50 percent and shows deposit control capability 50 F higher. These properties have been confirmed in various laboratory tests including; the Corrosion-Oxidation Stability Test, Alcor Deposition Test, Vapor Phase Coker, Erdco High-Temperature Bearing Test, Ryder Gear and the Mobil Thin Film Oxidation Test. The closely controlled low-temperature viscosity of Mobil Jet Oil 254, along with its low pour point (below -54 ºC), ensure good low-temperature fluidity to permit starting and lubrication at temperatures as low as -40 ºC. In extensive laboratory testing and in-flight experience, Mobil Jet Oil 254 also exhibits excellent bulk oil stability at temperatures up to 232 ºC (450 ºF) for extended periods. The evaporation rate at these temperatures is low enough to prevent excessive loss of volume. The load-carrying ability of Mobil Jet Oil 254 comes from its synthetic base stock viscosity and, therefore, is not subject to loss from viscosity index additive shear. The lubricant has excellent resistance to foaming."
The viscosity of 254 is around 5.3 cSt so I would be concerned about too much thinning of the other oil. If one used a thick 10W30 or 10W40 mineral oil with about 10% 254 and an oil analysis program it would be interesting to see how the UOA numbers stack up. My concern is that without a UOA, you are running a blind experiment.
The hindered esters should certainly keep the engine clean.
