Circa 1972 Evinrude 18hp - oil mix ratio?

[Clement]

I just bought an old Evinrude 18hp 2 cylinder "Fast Twin". The guy that sold it to me wasn't sure about the fuel mix ratio, maybe 16:1. Does this sound reasonable?

I'll also try to get in touch with evinrude and see what they have to say.

 

[1 FMF]

no
I have an old 18hp evinrunde, 1970-1980 era I believe, I will have to check. I'm pretty sure mine is 100:1, and certainly no richer than 50:1. I've been running mine around 75:1, because I run it wide open all the time. I do know that when I do a 3 gal mix at 50:1, it smokes bad at idle, and that's how you can usually tell you have it mixed too rich. And periodically check the spark plugs.
If you can get the model, year and serial # of the motor, definitely check with evinrude. But I can almost guarantee you its not 16:1.

I have mine on a 12ft achilles raft, which is rated for 10hp. I need new floorboard stringers, they all broke

 

[Drstressor]

The recommended ratio was 50:1 after a breakin at 25:1.

 

[Clement]

Thank you. This'll help keep a whole bunch of unburnt oil out of the water.

Can't wait to get the boat out. It is a 17' aluminum. It may be a little underpowered, but I'm not looking to waterski, so that's no problem.

 

[Cujet]

Ditto for the 50 to 1

Chris

 

[pmt]

I have owned a 1973 Evinrude 18 HP since new. Very reliable for all these years, but two problems that bug me: 1) Just drinks fuel at full throttle. 2) It smokes a lot. When backtrolling the smoke cloud actually makes me nauseous.
I helped the fuel consumption problem by running at only 1/2 to 3/4 throttle once the boat comes up on plane. Yes - it's not quite as fast, but not that much slower and seems to consume much less fuel. The smoking is tougher: I set idle screw adjustment lean as possible, tried fully synthetic Pennzoil outboard oil - nothing worked. I am now trying an 80:1 fuel/oil mix instead of the recommended 50:1 mix - seems to cut smoke some. My reasoning is that with today's improved oils (compared to 1973) engine should be able to handle a lower oil mix. Any comments?
Thanks.

 

[SteveD2]

quote:

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Originally posted by 1 FMF:
no
I have an old 18hp evinrunde, 1970-1980 era I believe, I will have to check. I'm pretty sure mine is 100:1, and certainly no richer than 50:1. I've been running mine around 75:1, because I run it wide open all the time. I do know that when I do a 3 gal mix at 50:1, it smokes bad at idle, and that's how you can usually tell you have it mixed too rich. And periodically check the spark plugs.
If you can get the model, year and serial # of the motor, definitely check with evinrude. But I can almost guarantee you its not 16:1.

I have mine on a 12ft achilles raft, which is rated for 10hp. I need new floorboard stringers, they all broke

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God I hope you're using something like Amsoil 100:1. NO 2 cycle motor will live very long on 75:1 dino oil...

 

[1 FMF]

how can you say that? I have a 10hp merc, late 80's or early 90's and that is 100:1.

I run Evinrude tcw3 oil in the 18hp

 

[SteveD2]

quote:

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Originally posted by 1 FMF:
how can you say that? I have a 10hp merc, late 80's or early 90's and that is 100:1.

I run Evinrude tcw3 oil in the 18hp

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NO, you don't. I feel sorry for your motors and anyone who might buy them. NO 2 cycle motor should be run at 100:1, unless you're using something like Amsoil, and even then most people use at least 80:1. Both of your motors should be run on 50:1 or MORE.

 

[Ugly3]

The correct mixture is 50:1 and the engine should be run with that mixture. There should be almost no smoke at higher RPMs and only a very little smoke at trolling speeds.

The notion that oils today are "better" than the old oils so "run it leaner" on oil is incorrect. Every outboard mechanic I have ever talked to has said to run the engines at the recommended ratio. Some have started their answers with "are you nuts" others start with a smurk and begin laughing. One guy told me to run at 100:1 because he likes to rebuild that particular engine.

There are all kinds of marine message boards. Get on some and find out for yourself.

 

[Drstressor]

What he said is so true! Run it at 50:1. If you are getting excessive smoke, your fuel mixture is too rich, not the gas/oil ratio. You probably need a carb rebuild.

 

[1 FMF]

I know that the 9.9hp merc I have, merc specified, at least back then, a 100:1 mix ratio. And the previous owner of it, who ran it all the time since late 80's, is a marine mechanic. And he told me told me to use 100:1 mix, quicksilver oil only. I will have to remember to ask him next time I see him. I may be mistaken, but i don't think so.

I look now at the mercury website and see all their small outboards are 50:1. I am running the fuel from my 18hp in my 9.9, which is somewhere between 50:1 and 75:1, and it smokes like a pig. The motor got tuned by the previous owner the beginning of this year, I know there is nothing wrong with the carb or mixture. I guess I will have to do some research on this issue.

found this, if anyone is interested
http://www.outboardrepairs.com/oil_mixture/

 

[SteveD2]

No, no, and no. Mercury NEVER recommended 100:1 for anything, and again, it should NEVER be used in any engine. OMC did for a short time recommend 100:1, but they quickly changed that to 50:1. If it smokes on 50:1, something is wrong with the engine, probably because it was run on 100:1. 50:1 is the bare minimum for ANY outboard ever made. If you use it on 100:1 you are doing serious damage every second the engine is running...

[ August 17, 2004, 04:10 PM: Message edited by: ZmOz ]

 

[1 FMF]

I think I stand corrected.
I asked this evening about it and it was omc like you said that had some 100:1 outboards. Nobody knew about the mercs, but he did say to run it 50:1 now, and that everything is 50:1.

But just so I know I'm not going crazy, there were outboards at least in the 10hp range in the early 90's that ran at 100:1? I can remember guys down the boatyard getting brand new outboards, and was always jealous because I couldn't afford it and was 10 years behind, and it was like the big craze running at 100:1. And the mix ratios on the 2-cycle oil bottles had 100:1.

When I bought my 18hp evinrude, which is somewhere around late 70's early 80's, the owner said he ran it 100:1. But I do feel more comfortable trusting you guys than him about it, but I've been running it around 75:1 the last 4 years and it still runs great. I would think if it was really too lean a mix that I would see evidence of it now. I run it wide open all the time.

 

[SteveD2]

Yes, there were smaller OMC engines that recommended 100:1, but again, that quickly changed because of the fact that 100:1 will quickly ruin an engine.

As for your engine, I can guarantee you that the compression would be much higher today had it run on 50:1 or better it's whole life. I run my inline 6 at 32:1 or more.

 

[pmt]

quote:

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Originally posted by pmt:
I am now trying an 80:1 fuel/oil mix instead of the recommended 50:1 mix - seems to cut smoke some. My reasoning is that with today's improved oils (compared to 1973) engine should be able to handle a lower oil mix. Any comments?
Thanks. [/QB]

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When I recently started to run a leaner oil mix to cut down on smoke, I felt comfortable doing so not just because I thought that newer oils are probably better - I'm using Pennzoil synthetic blend.
I work in engineering at a mobile equipment company (which will remain nameless since corporations don't like having their names bandied about websites).
Anyway, a guy I used to work with (he is now retired) had previously worked at an outboard motor company back in the 1970's (which will also go unnamed). He said their test engineering dept would test their outboard motors with 100:1 oil/gasoline mix to see how their engines would hold up if customers screwed up and mixed the oil way too lean. He said that as long as the oil was well mixed with the gas, they never had an engine failure or saw any engine damage using 100:1 mix. However, when they tested at 200:1, they would occasionally stick a piston. The company never recommended anything other than 50:1 mix, but they knew that screwups by their customers in mixing the oil would very likely not hurt their engines.
So maybe I'm taking a small risk running at about 80:1, but I'll see how it goes.

 

[Drstressor]

The problem is that the OMC 100:1 tests were conducted at the bench,probably with engines running under constant load and using freshly mixed fuel. There were lots of engine failures in the field. Reality sets in when you add variables such as stale or poorly mixed fuel, poor planning hulls, overloaded boats, cold starts, hard acceleration before warm up, and general real world abuse. The maximum load on engine parts takes place as you as the engine builds rpm while bringing a hull onto plan. Oil injection systems decrease the gas to oil ratio at intermediate rpm during acceleration. You can't do that with a fixed gas to oil ratio. You need enough lube for the worse case scenario at all times.

 

[joee12]

DrStressor, I could not agree more. Add hot summer days to the list. I know here it gets 105-110 with the heat index. -Joe

 

[blano]

Yamaha presently reccomneds a 100:1 ratio with regular tcw3 oil. The main problem with using less oil is the fact that it leads to less residual oil in the motor and more corrosion. Yamhas have been known to have bearing failures on wets years because of this. Thats why I run 50:1 in everything. BTW Mercury outboards smoke a little no matter what. Their transfer port arrangment is no where near as good as Yamahas or OMC's which results in the smoke and less fuel mileage.