lead additive?

[grizzly]

friend of mine just got a '57 mercury 20hp, and was wondering if he needs to use lead additive. and if so how much do you use? what do you guys do with outboards that old? i've looked at other posts but not finding an exact answer for one this old

 

[phased]

The lead in gasoline was put there as a cushion for the valve train in stem type valve engines. When we switched to unleaded gas engine manufacturers started installing hardened valve seats that would hold up without the lead cushion. Since outboards use 'reed' valves the use of lead is not necessary.

 

[bassboy1]

Lead additive is not needed, as mentioned. Another common misconception is that with todays modern synthetic oils, you can run less than the recommended mix rate. While that may work with a few motors, you should run most of those older ones at the same premix ratio as was specified when that motor was new, even if using new synthetic oils.

 

[grizzly]

thanks guys, that is what i needed to know. i searched the previous posts but never saw an explanation as to why it was not needed, appreciate your help.

 

[Captain Ahab]

Nice job Phased! Awesome answer

 

[Loggerhead Mike]

lead was also primarily used as an octane booster. i notice a big difference between regular and hightest in my old motor