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Old 29-11-2022, 14:22   #1
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Oops - added the wrong oil to 2-Stroke outboard tank

I just filled my outboard tank with 25 liters of fuel and mistakenly added 500ml of 10W-40 motor oil for a 50:1 ratio mix. I'm in the Caribbean (St. Lucia)

I am looking at 3 options:
  1. Dump it at a local boatyard and start again
  2. Use as is and expect some fouling on the plugs and dirty exhaust
  3. Add 500ml of good 2-stroke oil to make a 25:1 ratio, which is what Tohatsu recommends for breaking in the 18HP 2-Stroke that I have
  4. ??? open to suggestions ???
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Old 29-11-2022, 14:41   #2
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Re: Oops - added the wrong oil to 2-Stroke outboard tank

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Originally Posted by Zanshin View Post
I just filled my outboard tank with 25 liters of fuel and mistakenly added 500ml of 10W-40 motor oil for a 50:1 ratio mix. I'm in the Caribbean (St. Lucia)

I am looking at 3 options:
  1. Dump it at a local boatyard and start again
  2. Use as is and expect some fouling on the plugs and dirty exhaust
  3. Add 500ml of good 2-stroke oil to make a 25:1 ratio, which is what Tohatsu recommends for breaking in the 18HP 2-Stroke that I have
  4. ??? open to suggestions ???
Option 1, for the cost of gas and oil it’s not worth it unless you have a larger container (50l min) to dilute with more gas and proper oil. If you go that option ignore the 4s oil you’ve added and mix as if it were straight gas at 25:1 as per manufacturer spec.
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Old 29-11-2022, 14:50   #3
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Re: Oops - added the wrong oil to 2-Stroke outboard tank

I refused to get on a dive rib to go to sea after seeing the coxwain top up the two Suzuki two strokes with engine oil, after pleading with him not to. We eventually compromised by me going and buying 2 stroke oil and then draining the oil tanks down before refilling and setting off.

Dump it rather than risk the outboard and lots of extra costs.

Actually give it to the locals, they will be grateful, if you explain.

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Old 29-11-2022, 16:18   #4
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Re: Oops - added the wrong oil to 2-Stroke outboard tank

You could drain it off into a container and then add it in smaller amounts to your automobile tank. A few mL of oil in a full tank of petrol won't hurt anything and you will get use of the paid-for fuel.

Jim
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Old 29-11-2022, 16:27   #5
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Re: Oops - added the wrong oil to 2-Stroke outboard tank

If it were me I would add maybe 250 ml of 2stroke oil to assure good mixing and run it. You might get a little smoke or plug soot, but I doubt it.
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Old 29-11-2022, 16:29   #6
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Re: Oops - added the wrong oil to 2-Stroke outboard tank

Just run it. A little extra smoke will be the only difference. Back in the day, two-stroke manufacturers suggested using 30 weight motor oil when two-stroke oil was unavailable.
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Old 29-11-2022, 16:44   #7
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Re: Oops - added the wrong oil to 2-Stroke outboard tank

Quote:
Originally Posted by Zanshin View Post
I just filled my outboard tank with 25 liters of fuel and mistakenly added 500ml of 10W-40 motor oil for a 50:1 ratio mix. I'm in the Caribbean (St. Lucia)

I am looking at 3 options:
  1. Dump it at a local boatyard and start again
  2. Use as is and expect some fouling on the plugs and dirty exhaust
  3. Add 500ml of good 2-stroke oil to make a 25:1 ratio, which is what Tohatsu recommends for breaking in the 18HP 2-Stroke that I have
  4. ??? open to suggestions ???

It doesn't matter much, any of those are fine. I wouldn't recommend using regular motor oil as a routine substitute but can't imagine that it's a big deal.

If it were me I'd probably split the difference and add 250 ml of good two-stroke oil to get a little bit of lighter oil and the TCW-3 additive pack in there.


I've had lots of engines apart over the years fwiw.
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Old 29-11-2022, 17:06   #8
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Re: Oops - added the wrong oil to 2-Stroke outboard tank

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Originally Posted by jt11791 View Post
Just run it. A little extra smoke will be the only difference. Back in the day, two-stroke manufacturers suggested using 30 weight motor oil when two-stroke oil was unavailable.
My old 1968 Evinrude's manual says, "If Evinrude Outboard Motor Oil should not be available, a good quality outboard motor oil or SAE 30 automotive oil may be used. The oil used should have Service ML-MM or Service MM marked on the container. Additional markings such as MS, DG, DM, DS, designate heavy duty and should be avoided. Also, low priced light duty oils (container marked only with ML designation) and multiple viscosity oils (SAE 10W-30, etc.) should not be used,"
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Old 29-11-2022, 18:09   #9
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Re: Oops - added the wrong oil to 2-Stroke outboard tank

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Just run it. A little extra smoke will be the only difference. Back in the day, two-stroke manufacturers suggested using 30 weight motor oil when two-stroke oil was unavailable.
That was 60 years ago with 60 year old engines. Oil and engines have come a long way. Modern 4s oil is designed not to burn and is full of detergents and additives. 25l in what I would assume is a 15hp or less outboard could be 5-10 hours or more of fuel. Carbon and ash buildup will happen even at high rpm, more at lower rpm. This will foul plugs and plug ports. Again for 25l of gas just replace it.
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Old 29-11-2022, 18:19   #10
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Re: Oops - added the wrong oil to 2-Stroke outboard tank

rbk, I agree with you, but you miss my point. The OP said he put 10W-40 oil in the fuel for his 2-stroke engine. Even my 1968 Evinrude's manual which allows SAE 30 automotive oil says "multiple viscosity oils (SAE 10W-30, etc.) should not be used,". I too say he should dispose of it. Damaging the engine for his dinghy so far from home would be "not good", and he should avoid the chance.
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Old 29-11-2022, 19:04   #11
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Re: Oops - added the wrong oil to 2-Stroke outboard tank

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rbk, I agree with you, but you miss my point. The OP said he put 10W-40 oil in the fuel for his 2-stroke engine. Even my 1968 Evinrude's manual which allows SAE 30 automotive oil says "multiple viscosity oils (SAE 10W-30, etc.) should not be used,". I too say he should dispose of it. Damaging the engine for his dinghy so far from home would be "not good", and he should avoid the chance.
Totally agree and I hadn’t quoted you. Though even now an SAR 30 is nothing like the 30 when that outboard manual was written. That’s why most oils these days always state ‘meets it exceeds xxx standards’.
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Old 29-11-2022, 20:01   #12
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Re: Oops - added the wrong oil to 2-Stroke outboard tank

I think about it like this:

This is Zanshin, and it is his o/b motor. If he feels like it, he could make the experiment to see how fast the plugs foul, and how badly.

I'm with Pete7 on this. It is that if you don't mind risking the long term usage of your own outboard, that's fine with me. Your boat, your choice. But Zanshin can also decide that a no risk policy about it will have more potential benefit for him. We're all individuals, with different experiences and skill sets.

We've had a number of outboards over the years, and never used anything but 2 cycle oil in any of them, all 2 strokes, of course. When you know what works, and weigh the savings of not donating the fuel, or as Jim suggested, "enriching" his gas automobile's tank with his mistake (assuming he doesn't drive only diesels, of course)--that just makes sense to me. The risk to the long term longevity by trying to find a way only slightly safer to deal with it seems imprudent to me. But then, we wear ours out before replacing them, except for the ones that were stolen.

Ymmv.

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Old 29-11-2022, 20:45   #13
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Re: Oops - added the wrong oil to 2-Stroke outboard tank

The mix ratio is 50:1. 50 parts gasoline to 1 part 10W40 oil in a fully diluted mixture will not impact the performance of the outboard or foul the plugs or ports.

We are talking running five gallons of gas/4 stroke oil mix on a one time basis.

By no means definitive but same conclusion after some backyard mechanic testing. See

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Old 29-11-2022, 23:36   #14
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Re: Oops - added the wrong oil to 2-Stroke outboard tank

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If it were me I would add maybe 250 ml of 2stroke oil to assure good mixing and run it. You might get a little smoke or plug soot, but I doubt it.


Correct solution.

You young blokes may not be aware of it but before oil companies fell totally into the hands of their marketing departments common or garden variety lubricating engine oil without additives was what was mixed with gas to make 2 stroke fuel.
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Old 30-11-2022, 04:11   #15
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Re: Oops - added the wrong oil to 2-Stroke outboard tank

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You young blokes may not be aware of it but before oil companies fell totally into the hands of their marketing departments common or garden variety lubricating engine oil without additives was what was mixed with gas to make 2 stroke fuel.
Yes, I have a 1963 Seagull outboard that would quiet happily run on that mixture . No way would I have run my Yamaha on it though, but I prefer to be risk adverse later in life.
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