It's the supposed benefits of the post-combustion lead oxide deposits that defenders of leaded gas cite. I have never heard anyone cite the lubricity of TEL it

It's the supposed benefits of the post-combustion lead oxide deposits that defenders of leaded gas cite. I have never heard anyone cite the lubricity of TEL itself. The most popular theory is that the lead oxide fouling reduces the occurence or effects of micro-welds between valve and seat surfaces, which otherwise produce abrasive particles that contribute to valve seat recession. While this theory is plausible, it has not been shown to occur under normal operating conditions in automotive engines, nor in aviation engines as far as I know. The final report from the EPA's Valve Seat Recession Working Group found no evidence that leaded gas reduces engine wear under any but the most extreme operating conditions: https://archive.epa.gov/international/air/web/pdf/vsr-finaldraft.pdf https://archive.epa.gov/international/air/web/pdf/vsr-finald... "In real world conditions, virtually no evidence of excessive valve wear has been found in vehicle or engine operation in normal everyday use, and several studies that monitored vehicles in actual daily service in countries that eliminated lead found no excessive valve wear."