Gassy oil -- octane the cause?

[BuellOnYamaha]

Sorry if this discussion is a repeat -- I tired to search and didn't find anything.

I just changed my oil (2012 Super Tenere) for the first time since the start of the season -- about 3k miles. It was pretty bad. Black with brownish streaks, even a bit of foam. Pretty distinct smell of gas.

So -- I'll be investigating injectors, rings, etc. as has been suggested on other threads.

But I also have a hypothesis I'd like some informed thoughts about. Could running lower-than-recommended octane gas be the cause?

In May I rode with some buddies down to the Smokies and while we were there, the great pipeline shutdown of 2021 hit. Many stations had no gas at all, others had only 87 octane. I angsted over putting it in my tank, but my friend made two compelling points: 1. you bike has an 02 sensor and will adjust to provide proper combustion and 2. what fucking choice do you have?

Observing no performance losses after three of four tanks-full, I switched to only using 87 all of the rest of the summer.

I had changed the oil just before the Smokies ride and did not note anything concerning about the condition of the replaced oil. That was the last oil change before this most recent one.

It's got me wondering. Is it possible that running lower octane fuel has resulted in under-combustion, in turn causing fuel leak-down to my crankcase? I've never been able to wrap my head around the chemistry of octane and what it means for engine performance, beyond I know it has something to do with oxygen, which has a lot to do with combustion. Regardless, I'm going back to factory recommended octane. I hope this resolves the issue as it is the easiest fix. I'll be interested to see if this change confirms my hypothesis.

My experiment isn't perfect as there are other variables I'm not controlling for. IE: the bike sat for a month in my garage in August, and then only went for a couple of short rides to work (5 miles each way). I did do a nice 250 mile ride this past weekend and I would have thought that would burn off any gas that had accumulated in my oil, but I guess not. My oil warning light came on at the beginning of this ride (which it's never done before) but went back off after a few seconds and stayed that way. This is what prompted me to change the oil as soon as I got home.

 

[WJBertrand]

Running regular where premium is recommended may cause over combustion, i.e. knocking and pinging, because the fuel burns too quickly. If this is ignored engine damage can eventually occur in the form of burnt or holed pistons in extreme cases. Higher octane fuels are designed to burn more slowly to avoid this. It is pretty doubtful that running regular in your bike in the absence of any pinging or knocking, would have any effect on the engine or the oil appearance.

In earlier days, fuel manufacturers would not include their full detergent packages in regular fuel that they would supply in their premium grades. I believe that changed decades ago (early 80s) when automakers and consumers complained loudly of drivability problems as EFI became widely employed. Those systems are more susceptible to gumming up and clogging than carbureted engines were. Such problems could also cause injectors to stick open and dump too much fuel. Too much raw fuel could affect the oil as you observed. What do your spark plugs look like? Is there evidence of rich running? Also are you making sure to run Top Tier fuel brands, regardless of grade?

So your problem seems like due to something else than simply octane.

 

[BuellOnYamaha]

I think I probably do have a bigger problem. I gen do stick with top brands but my last fill up of the weekend was at a mom and pop store in rural Vermont. Not sure who their fuel provider is.