Lead Additive To Fuel
- Thread starter BobbyG
- Start date
Tudorp
Member
I believe all fuel today is lead free. Has been since the late 70's. Lead was used as a lubricant, as well as forming a seal for the valves in early engines. Todays engines have hardened valves and valve seats so no longer need the lead in the fuel. If your motor has been rebuilt over the past 20 years or so, odds are it has hardened valves and guides. Correct me if Im wrong, but that is how I understand the need for leaded fuel years ago. I generally just use Marvel Mystry oil in my gas tank as an additive to sooth the valve train.
Last edited:
1937pickup
Well-known member
As I understand the lead issue flatjack9 has the right question to ask. Engines earlier than 8bas do not need lead. Due to poor quality of gas they had hardened seats, which I believe are only needed on the exhaust valves.
Pete
BANNED
I have experimented with many fuels and additives over the years.
Tetraethyl lead was introduced in the 30's as an octane
booster/antiknock compound. It was beneficial as a valve stem
lubricant also.
IT IS EXTREMELY TOXIC! It is not something a back yard
Joe Mechanic should be playing with.
It can still be found in 100LL aviation gas in amounts of 4 cc
per gallon. This is the highest quality gas available to the public
these days although you have to buy it in cans or barrels unless you
are pumping it into a plane.
ford38v8
Well-known member
Old Henry, "Just in case it helps" is the best and most popular reason given for using an additive! Congratiulations for being right on top of that one!
Actually, the additive you chose is very helpful for one troublesome problem we all seem to have at one time or another:
Using additives in your gas has a beneficial effect on your wallet in keeping it trim and fit, which translates to no ugly bulging around the hip pocket.
Actually, the additive you chose is very helpful for one troublesome problem we all seem to have at one time or another:
Using additives in your gas has a beneficial effect on your wallet in keeping it trim and fit, which translates to no ugly bulging around the hip pocket.
Uncle Bob
Well-known member
As Pete mentioned, the primary purpose of tetraethyl lead was to control knock by altering the rate of burn of the fuel molecules.
The notion of the lead as a "lubricant" is pretty much fictional, or to be more charitable a misinterpretation. The former Union Oil Co. did exhaustive (pun intended) analysis and produced an SAE paper defining the unintended positive outcome for exhaust valve life, as did others. The lead additive was disolved in solution, that's why you never had lead balls or film at the bottom of your tank. In the combustion process the lead became oxidized and it was a portion of that lead oxide that "plated out" on the exhaust valve (obviously wouldn't affect intake because it was still in solution when it went past that) and seat on it's way out. As those of you who are familiar with welding have learned, it's difficult to weld dirty (as well as dissimilar) metals. Because of the high heat (under certain extreme operating conditions) the exhaust valve endured it would form microscopic welds from valve face to seat that were broken as the valve opened. Over time those breaks accumulated to be recognized as valve/seat erosion. The lead oxide had the effect of dirtying the valve/seat interface preventing welding.
The notion of the lead as a "lubricant" is pretty much fictional, or to be more charitable a misinterpretation. The former Union Oil Co. did exhaustive (pun intended) analysis and produced an SAE paper defining the unintended positive outcome for exhaust valve life, as did others. The lead additive was disolved in solution, that's why you never had lead balls or film at the bottom of your tank. In the combustion process the lead became oxidized and it was a portion of that lead oxide that "plated out" on the exhaust valve (obviously wouldn't affect intake because it was still in solution when it went past that) and seat on it's way out. As those of you who are familiar with welding have learned, it's difficult to weld dirty (as well as dissimilar) metals. Because of the high heat (under certain extreme operating conditions) the exhaust valve endured it would form microscopic welds from valve face to seat that were broken as the valve opened. Over time those breaks accumulated to be recognized as valve/seat erosion. The lead oxide had the effect of dirtying the valve/seat interface preventing welding.
keith oh
Well-known member
Very good explanation Uncle Bob. The stuff they call lead substitute such as" Insted of Lead, SD2 and many others have absolutly no relation to Tetraethyl lead and will eventually cause a kind of gel in the bottom of sediment and or float bowl. The stuff does benifit one group, the ones manufacturing and selling the crap.