[woofa.express]

Originally Posted by rotorwrench

There are distinct differences between air cooled aircraft engines and any other type. Most have large bores compared to automotive engines to give them the displacement that will develop horsepower in the range needed. Many are still carbureted and the rest are mechanically fuel injected. There are few with channel chrome plated cylinders now days but there may be a few still running. They run in the neighborhood of 215 degrees F and more depending on conditions. These are extremes for piston engines. It takes a strong detergent quality to scavenge the combustion bi-products that get past the rings. It also takes a minimum of SAE 50 viscosity index to do a decent job of lubricating. Mineral based ashless dispersant scavenging additive can easily be blended in and still hold the viscosity pretty well at 100 degrees C since there is a wide band of viscosity index available in mineral based lubricant stocks. Ester based synthetics are a different story. The are strictly a low viscosity lubricant that has to have viscosity building polymers blended in to give it the SAE 50 viscosity. These polymers break down quickly at high temperatures. This is why many of the synthetic aviation motor oils are semi-synthetic which is a blend of mineral and synthetic based stocks. Ashless Dispersants work better in mineral based oil than they do in synthetic so this is another reason for the mix. Aircraft that fly up in the colder atmosphere can get away with using semi-synthetics but helicopters and smaller aircraft usually stay in the lower altitude ranges. Take off for airplanes is usually full power until a cruise altitude is reached and helicopters run at high power settings anytime they are hovering or gaining altitude so they get wrung out pretty well in normal operations.

I learned a long time ago not to use synthetics in the helicopters. They would never last on the stuff. Aeroshell W100 or W100+ are the most common used. The plus has TCP as an additive for Lycoming engine cam follower well being but can not be used in engines with integral clutches or overrunning clutches since they might slip with that oil. Straight mineral is only used for break in.

Automotive engines have no real comparison to aircraft engines other than they are a reciprocating piston design.

I endorse what rotorwrench has written.