Part-synthetic, aviation piston engine lubricant

An aviation piston engine lubricant having no metal-containing additive content, the lubricant comprising:

• (a) a base oil consisting essentially of a mixture of
• (i) at least about 50 wt % based on the total weight of the lubricant of a mineral oil base stock having a viscosity in the range of about 5 cSt to about 25 cSt at 100° C. and containing one or more mineral oils selected from solvent extracted mineral oils in the range of 150N to 600N mineral oils and mixtures thereof with solvent extracted bright stock, and
• (ii) about 15 to about 40 wt % based on the total weight of the lubricant of a polyalpha olefin fluid having a viscosity in the range of about 4 cSt to about 40 cSt at 100° C.;
• (b) at least about 3 wt % based on the total weight of the lubricant of an ashless polyisobutylene succinic anhydride/polyamine (PIBSA/PAM) dispersant having a nitrogen content of 1.4 to 1.8% and an acid number as determined by ASTM D664-Buffer B end point of from about 5 to about 8;
• and
• (c) an effective amount of one or more ashless additives selected from the group consisting of antiwear agents, extreme pressure agents, metal passivators, and antioxidants.