oil ratios

[jdsgrog]

I've got a couple of '50's outboards that require 24:1 ratio and some '60's outboards that run 50:1 ratio. I was wondering why there was such a drastic change (over double the ratio) from the '50's to the '60's. Did the build technology and materials change requiring less oil in the fuel? Or did the oil technology change?

I have read post's on this forum that state that a 24:1 ratio is no longer needed because of the change in oil technology and quality. Just wondering if this is the case or not.

 

[rjezuit]

Re: oil ratios

Use the original specified ratios. Some will differ with this opinion, but more oil will not blow up your outboard, less oil might. The change was going from plain bearings (bushings) to roller bearings. There are some years where they were a mix of both, but you have to lube the plain bearings more since they are sliding contact, not rolling contact. The new synthetic or semi synthetic smoke and pollute less, so try those if you are concerned. The new oils do lube better so some say you can decrease the oil ratio, but the only way to find out you were wrong could be to smoke a motor. Rick

 

[kbait]

Re: oil ratios

Omc changed to roller bearings in '65 (but perhaps not all models exactly that year, I've heard). Omc calls for pre-'65 @ 24:1 and post-'65 at 50:1.

I've run the older ones at 32:1 conventional 2-stoke oil for MANY years w/o issue, and I started running the newer ones @ 100:1 with this: http://www.amsoil.com/StoreFront/ato.aspx

I also use non-oxygenated fuel (no ethanol) that a local station added. I like the amsoil for the newer ones. Costs twice as much, but you use half the amount and no plug fouling and less smoke clouds. Just be sure to fog your motor before storage, as there's bound to be less oil residue on the internal parts to keep from corroding.

 

[JB]

Re: oil ratios

In 1964, OMC re-speced all OMC made engines before 1964 to 24:1 using TC-W oil, and all post 1964 engines to 50:1.

Some of this was because of improved oil technology, some because of improved engine technology, but mostly because of marketing considerations because other makers were trumpeting 50:1.

Recently, BRP has published revised listings of spec oil ratios. I suggest that you find that listing and follow it. DO NOT be persuaded by people who violate OMC/BRP specs and get away with it. That includes using non-TC-W3 certified oil. Those folk are walking barefoot in snake country.

My policy of doing exactly what the maker says to do gets a little tangled up here, because if you look long enough you can find up to 4 different ratios recommended for the same engine at different times.

Use the ratios currently specified by BRP.

 

[jdsgrog]

Re: oil ratios

I have no problem using a 24:1 ratio. I was just curious, but the explanations make sense. The only issue I see with the 24:1 ratio is that there seems to be more chance to foul the plugs vs. the 50:1 ratio. I'll just check the BRP resources just to make sure.

 

[jdsgrog]

Re: oil ratios

Oh, one other thing, does anyone know where to get the oil ratio spec sheet?

 

[Vic.S]

Re: oil ratios

How about http://www.evinrude.com/en-US/About.Us/FAQ/Oil.Fuel.htm?

 

[rolmops]

Re: oil ratios

Wow,how times change.
If you really want to go by the exact rules you should also use SAE 30 engine oil on your fifties engine in which case the mix will be exactly as the manufacturer promoted

 

[JB]

Re: oil ratios

The exact rule is to go by what the maker currently recommends, not what they recommended 50 years ago.