The following article may suprise you, it did to me. I pass it along due to the fact that the writer of the article is so highly qualified beyond question.
Gordon Millar has written numerous technical articles as well as over 80 articles on the history, design and restoration of antique and classic marine engines, an area in which he has become a recognized expert. An SAE Fellow and a member of SAE International since 1949, Gordon Millar was elected to the National Academy of Engineering in 1975 and, in 1984 served as SAE President, the same year that he concluded a noteworthy career at John Deere.
Gordon Millar, SAE president in 1984, also
earned his doctorate in mechanical engineering from the
UW in 1952. His research was in "Flame Temperature
Measurementsa sa n Aid to Internal Combustion Engine
Analysis." At the time of his SAE presidency, he was
vice-president of engineering for Deere & Company.
Millar now enjoys retirement in Daytona Beach, Florida.
Doing a search today for Mr. Millar brings up a company called Motortech, Inc., which seems to exist to hold patents, no phone number is given, but the following link has some info on the board of directors.
I recall he used to write articles for Classic Boating Magazine. I certainly hope he is doing well today.
Here is a link to Mr. Millar
With these credentials, I defer to Mr. Millar when it comes to marine engines and their need for lead additives, etc. I hope you all find the following article by Mr. Millar to be of interest and value.
"Immediately after World WarI I worked for the Ethyl Corporation in the
design of engines that would run comfortably on tetraethyllead.
Tetraethylead was invented by Thomas Midgely working for Charles Kettering
and introduced as an anti-knock additive in 1922. It never, and I repeat
NEVER was ever used nor would the engine benefit from its use as a high
Design changes necessary for engines to scavenge tetraethyllead deposits were
the use of valve rotators, counterbored valve guides, hard-faced valves and
seat inserts, and the use of an interference angle between the valve face and
valve seat. The deposits of tetraethyllead served no useful purpose as a
lubricant with the minor, and very minor, effect they might have in
inhibiting valve seat recession but only in engines that do not use hardened
valve seats, and these are few and far between.
During World War II the Germans introduced iron carbonyl as an anti-knock
additive in their synthetic avgas. Although this material worked well to
suppress knock, the horrendous deposits of Fe2O3, (rust) limited engine life
to not much over 100 hours. For the Germans this did not matter much as their
war planes seldom lasted that long in combat anyway.
During the '50s Mercury would not warrant engines that were run on leaded
fuel and insisted that their engines be run on unleaded straight-run marine
fuel until this fuel was discontinued in the early '60s.
All our antique and classic marine engines were designed to run on the
standad unleaded 82 octane number straight-run marine fuel. There is
absolutely no need for any kind of additive whatsoever to replace
tetraethyllead in our antique and classic boat engines because it was not
there in the first place. You run the serious risk when you add a
tetraethyllead replacement (which is unneeded) that you will form combustion
chamber deposits and serious engine damage will result.
As a parting comment, there is no need to add anything to the fuels and
lubricants available on the market as they are the result of literally
billions of dollars of research and are the finest products we have had
available for engines ever.
Gordon H. Millar, P. E. "
I found the article to be enlightening, and a bit counter to my sense of need to provide good care for my engines. Even with the assurance from someone as well credentialed as Mr. Millar, providing such qualified advice, I must admit I have still used some additives now and then. Mr. Millar would probably say it was a waste of money.