TD-20 Johnson oil/gas mixture revisited

[Grampsmotor]

The owners manual to my "new" TD-20 shows 1/2 pint (8 oz) per gal. I've seen it stated here that a 24:1 or 4 oz per gal is the correct mix.

Can anyone clarify why the restated amount of oil? The motor does smoke a fair amount at the 8oz/1gal mix, but I don't want to damage the motor. Have oil mix requirements changed with improved oil technology since '49?

Thanks for any input.

 

[JB]

Re: TD-20 Johnson oil/gas mixture revisited

Ahoy, Gramps.

Welcome to iboats.

When your engine was built, 1946 to 1949, specially formulated outboard oil was not available. OMC called for a 16:1 mix (8oz/gal) using 30W non-detergent motor oil.

In 1964, when TC-W outboard oil became available, OMC changed the recommended mix to 24:1 using TC-W oil for all OMC engines built before 1964 and 50:1 for 1964 and later engines.

If you want to use 16:1 with 30W motor oil it would do little or no harm, but smoke a lot more and need decarbonizing and plug cleaning more often.

To use TC-W3, the current standard for outboard oil, mix 1 quart oil to 6 gallons gas or 5-1/3oz per gallon.

 

[Grampsmotor]

Re: TD-20 Johnson oil/gas mixture revisited

Thanks JB, this helps. 24:1 it is.

 

[F_R]

Re: TD-20 Johnson oil/gas mixture revisited

Little typo there, JB? One pint to 6 gallons is 50:1. But of course you know that. Somebody else might get confused.

 

[JB]

Re: TD-20 Johnson oil/gas mixture revisited

Thanks, Frank. I fixed it to 1 quart oil to 6 gallons gas.

Sorry about that, Gramps.

 

[samo_ott]

Re: TD-20 Johnson oil/gas mixture revisited

Of course gramps doesn't know it but he stumbled upon one of the more controversial topics on the forum!