1959 18 hp johnson

netman · Feb 23, 2010

Anyone know what the proper oil to gas mixture for a 1959 johnson 18 hp seahorse?

Whoopbass · Feb 23, 2010

I think its 8 ounces to the gallon.
Oil was not as good as it is now so you could probably run synthetic and use about half that amount.

You might go onto one of those old outboard sites and see what those guys run. I'm sure some of them have experimented to see how little of oil they can run where it won't hurt the motor.

crazymanme2 · Feb 23, 2010

The proper mix for your '59 Johnson is 24:1. That is 1 qt. of outboard oil to 6 gallons of 87 octane unleaded, alcohol-free gas.Use only Champion J6J or equivalent plugs, gaped at .030.The motors in those days didn't know what alcohol was & becomes a problem with some of the rubber fuel component's.

netman · Feb 23, 2010

crazymanme2 said:
The proper mix for your '59 Johnson is 24:1. That is 1 qt. of outboard oil to 6 gallons of 87 octane unleaded, alcohol-free gas.Use only Champion J6J or equivalent plugs, gaped at .030.The motors in those days didn't know what alcohol was & becomes a problem with some of the rubber fuel component's.

Sweet deal. Thanks. I have been googling and finding a variety of answers ranging from 24:1 to 32:1 to 50:1 and i was just banging my head against the wall trying to find the right answer. I live in MN where the 87 octane gas is actually e-10 (ethanol....not good)....Is 91 octane (non e-10) be ok to run with the same mixture?

That is good to know on the spark plugs for type and gap as well. The guy I bought the boat and motor from said he just put in new plugs last spring and had put on just a few hours on the motor since. I will check the gap however and make sure he used the correct plugs.

Thanks again for the help.