From: utzoo!watmath!watcgl!dmmartindale Newsgroups: net.misc Title: Re: Regular vs Unleaded Gas Article-I.D.: watcgl.185 Posted: Fri Feb 11 02:03:18 1983 Received: Fri Feb 11 07:14:50 1983 References: utcsrgv.998 There is no metallic lead in "leaded" gasoline. The octane-increasing additive is tetraethyl lead. I don't know what it turns into during combustion, but I would expect a lead oxide of some sort. Whatever it is, it tends to deposit on things, and provides lubrication for the valves and valve seats. Older engines need this; newer ones use better materials in the valves and seats and can withstand running with no help from the lead byproducts. Presumably they will still last longer if the lead is around. It can be a mixed blessing, though - lead deposits on the valve stems can cut down gas flow through the engine, and sparkplugs can become lead-fouled (a very common occurrence in aircraft burning 100/130 octane fuel, which has lots of lead in it).