Type gas for Johnson

[mkmnc]

What type of gas does a 1966 Johnson 33hp model# RXE-14 call for?<br /><br />I have been running Hi test because I thought do to age of engine that it might ignite better.<br /><br />Am I way off base with this and will the higher octane hurt the engine if that is not what the motor is suppose to run?<br />Not to mention the added cost!<br /><br />Mike

 

[Paul Moir]

Re: Type gas for Johnson

No, the engine does better with lower octane gas. Deposits don't form as quickly & you seem to get a more complete burn. <br /><br />Up here, the high octane fuels seem to contain a lot of additives which have caused me problems with old outboards. Specifically, melted fuel lines, cracked fuel pump diaphrams, stripped out sealants, and sometimes a "washing out" of the fuel lines that throws a bunch of junk in the carb.<br /><br />So basically, I stick to 87 octane gas and use fuel stabalizer to make starts easier (as the fuel gets old). Actually, the only place I really ever notice that is on the smaller engines that don't consume fuel very fast.

 

[timmathis]

Re: Type gas for Johnson

I have better results with the mid grade. <br />(89 octane)

 

[JB]

Re: Type gas for Johnson

I am with Paul on this. The effective compression ratios of two stroke engines offer nothing that takes advantage of high octane fuel when correctly timed.<br /><br />Some of the potential additives in high octane fuel will increase deposits and threaten fuel system components. Tetraethyl lead was one of the worst of them.<br /><br />Modern, lead free regular (87 octane in the US) is superior to any fuel available when your engine was built except Amoco "white" gas (about 80 octane) which OMC recommended when available.

 

[mkmnc]

Re: Type gas for Johnson

Thanks, I'll save some money and use regular.<br />Mike

 

[rg33]

Re: Type gas for Johnson

Originally posted by JB:<br /> I am with Paul on this. The effective compression ratios of two stroke engines offer nothing that takes advantage of high octane fuel when correctly timed.<br /><br />Some of the potential additives in high octane fuel will increase deposits and threaten fuel system components. Tetraethyl lead was one of the worst of them.<br /><br />Modern, lead free regular (87 octane in the US) is superior to any fuel available when your engine was built except Amoco "white" gas (about 80 octane) which OMC recommended when available.

I have a 1988 Mariner 150hp, V6 and the owners manual recommends leaded regular or unleaded premium , but not unleaded regular. Manual was printed in 1987, would present conditions warrant a change?

 

[JB]

Re: Type gas for Johnson

That's a mystery to me, rg33.<br /><br />I cannot imagine why they would make such a recommendation, but I wont recommend against what the maker says.<br /><br />I see no reason, none, for recommending leaded fuel for a 2 stroke, or premium of any kind except for a highly modified racing engine. Perhaps they were trying to steer users away from the kerosene they sell as gasoline in some countries.

 

[BoatBuoy]

Re: Type gas for Johnson

From another website:<br />"The number we most often associate with octane is the "Anti-Knock Index", or the "Pump Octane" number. This rating is an average of two different measurements; the Motor Octane Number, and the Research Octane Number. Both of these measurements are taken using a special single cylinder test engine that has a variable compression ratio. The RON measures the knock resistance of a fuel during low RPM, light load conditions, while the MON is representative of high-speed, high load operation. As a result the MON will always be lower than the RON"<br /><br />With that being said, RON is what is used in Europe while "Pump Octane" is used in US. Could it be that maybe the manual was taking into account the differences in 1987?

 

[rg33]

Re: Type gas for Johnson

This may be a question for a marine mechanic. I remember in the 80's, unleaded fuel was believed to causes valve and valve seat damage because they were not hardened. I remember having a modified Pontiac Trans Am were I was told to add octane booster to unleaded premium gas. Later, the way the octane rating was calculated became a big discussion in auto magazines (no internet yet). I wonder if my valve system would be suspect?

 

[JB]

Re: Type gas for Johnson

They were talking about 4 stroke engines, rg33. Two strokes have no valves.

 

[rg33]

Re: Type gas for Johnson

Then I will have to do a search on the fuel used on similar motors to mine, thanks.

 

[JB]

Re: Type gas for Johnson

Huh?<br /><br />I guess that's what happens when you hijack a thread, rg33.<br /><br />Your Mariner is a 2 stroke engine. It has no valves. I know of no argument for using leaded gas in any 2 stroke, except what you quote from a 17 year old manual.<br /><br />If I had your engine I would run 87 octane unleaded and TC-W3 oil.

 

[rg33]

Re: Type gas for Johnson

Sorry, if this is what I did. Just trying to join in. You're probably right, got the TC-W3 synthetic blend oil, will try the fuel next outing.