Why is Aviation Oil Different from Automotive Oil?

Shashwat Dwivedi
11 hours ago
2 min read

By Shashwat Dwivedi Published: 15 December 2025 | Updated: 15 December 2025

Understanding why aviation piston engine oils differ from automotive oils in composition and performance.

Anyone with a keen interest in aviation or even slight enthusiasm for aircraft has probably wondered about this at one point: why do aviation piston engine oils offer such limited anti-rust and anti-wear protection compared to automotive and heavy-duty engine oils?

The answer lies in the certification standards for oils used in piston engines. Aviation oils must comply with the Mil-L22851/SAE 1899 specification, which ensures the oil performs reliably in all spark-ignition aviation piston engines without causing operational issues.

The composition of these oils is another key factor. Heavy-duty automative engine oils include ash as an additive, which is strictly prohibited in aviation engine oils. For anti-wear protection, automotive oils often contain zinc dithiol phosphate (ZDTP).

ZDTP works by forming a protective coating on engine parts, a process known as sacrificial lubrication. This coating wears away gradually, protecting critical components such as cams and lifters. As a result, ZDTP significantly improves the load-carrying capability of the lubricant compared to base oil alone.

However, ZDTP is not without drawbacks. While it is highly effective on iron-based components like cams and lifters, it can damage softer metals such as silver or copper. Many aircraft engines use copper alloys for exhaust valve guides, and ZDTP can tarnish these surfaces, reducing clearance and eventually causing valve sticking. Similarly, in radial engines, ZDTP can attack silver used in master rod bearings, compromising their load-carrying capacity.

This explains why automotive and heavy-duty oils provide superior anti-rust and anti-wear protection compared to aviation oils. They contain advanced additives that are not permitted in aviation piston engine oils due to compatibility and safety concerns.