Oil and gas mixture issue - please help

[boatinrocks]

Hey there!

I'm quite new to boating and am definitely loving it but am in dire need of some advice from some experts.

Imagine you had a Johnson 20HP 2-stroke outboard motor and a 10 gallon (40Litre) external tank. If you filled the tank with the proper oil:gas ratio and then,when your tank was at the 3/4 mark (several days later), someone topped it off with straight gas and no oil, what would happen to your motor? Would diluting the oil by that much cause severe permanent damage? Or would you need to have a much weaker concentration of oil to actually cause damage?

Secondly, if damage were to happen, would it happen within moments of adding the gas, or would it occur much later as the initial gas/oil mixture was consumed?

Thank you for taking the time to help me out.

 

[jimdd810]

Re: Oil and gas mixture issue - please help

Yes it could be hurting your motor. As for how long or how much damage depends on how hard you run it. Are you sure about the amount of gas added if you are you can add more oil even if its a little rich.

 

[F_R]

Re: Oil and gas mixture issue - please help

Rounding off the numbers, I calculate you wound up with a 61:1 mix. They will run on 100:1 (but don't do it). So I don't think you damaged it. But dump in another 9 or 10 ounces of oil and you will be fine.

 

[d.boat]

Re: Oil and gas mixture issue - please help

Rounding off the numbers, I calculate you wound up with a 61:1 mix. They will run on 100:1 (but don't do it). So I don't think you damaged it. But dump in another 9 or 10 ounces of oil and you will be fine.

My brand new VRO/OMS pump seems to avearage about 55:1 at cruise to WOT, so that might be a bench mark worth thinking about (meaning 60:1 isn't ridiculously off and not likely to harm an engine if used temporarily and not as a habit).

 

[boatinrocks]

Re: Oil and gas mixture issue - please help

Hey Everyone, thank you for your input. I really appreciate your help. I will definitely be more cautious with my mixtures!

 

[d.boat]

Re: Oil and gas mixture issue - please help

Hey Everyone, thank you for your input. I really appreciate your help. I will definitely be more cautious with my mixtures!

This is one of the reasons I personally think that a up to date and maintained automatic oiling system is probably better than premixing in some, if not all, situations, especially with large built in tanks. I premixed forever and occasionally knew, or thought I had forgotten oil, (which I added of course, or re-added if I was unsure - better late than never or too rich). I'd venture to guess there were times I topped off one or both of the two tanks and had a brain fart or got distracted by my kids or friends interrupting me, and flat out forgot to add oil or mis-calculated and never corrected it. I'm not saying this was regular, just that over the years I know it probably happened. I don't believe there's any data, but oiling can fail in both systems regardless of the old adage "pre-mix and have peace of mind". The mind is peaceful if it doesn't know it messed up!