Av Gas typically has much higher concentrations of TEL in it than is used in automotive
fuel. Most light air craft use 100LL and high performance recip engines often require 130
octane which can run as high as five times the amount in auto fuel. Because of this it also
has much higher levels of lead scavenging compounds. These don't do their job at lower
temperatures such as idle so it’s recommended that engines be warmed up and shut
down at higher engine speeds such as 1200-1500 rpm to prevent plug fouling. At higher
temperatures the lead bromide will vaporize and gets pumped out of the cylinder, it re-
condenses when it's expelled into the cooler air. the auto engines are operated a lot of the
time at lower speeds which do not produce a high enough temperature to vaporize the
compounds so they deposit on the valves, pistons and plugs.
Denny Graham
Sandwich, IL

Denny G
Sandwich, IL