fuel in the oil issue/question

[GLoweVA]

I've been reading over the years about how you guys warn about running the engines with gas in the oil.
I'd like to know why.
Sure, gas is a solvent and will definitely thin the oil out, but is that such a bad thing? (too much I can see would be bad) (though, the seafoam engine oil cleaner/flush stuff isn't harmful?)

You guys talk about wiping bearings and stuff. I'd like some details and maybe some symptoms of what this might be like.

I guess the reason that I ask, is that, maybe in the very distant past when I first got my bike, there may have been times when the carbs had overflowed. I never saw an increase in oil level in the sight glass(at least as far as I can remember), but that doesn't mean that some might not have gotten in there.
Heck, just the other day, my SG overflowed and came pouring out my airbox, I doubt any got in the engine. (I've got a jackstand under the front engine cross bolt.)

But why should I be so paranoid/worried about it?

Hasn't some of us used some crazy stuff in the cylinders to free up stuck ones? Wouldn't these 'lubricants' also be bad?

[natemoen]

As you said gas is a solvent. The solvent destroys the lubrication properties of the oil. The next question would be, how much gas in the oil is too much? Don't know, why chance it! Oil is much cheaper than engines. When in doubt change it out.

As to getting cylinders unstuck, doesn't matter cause you relubricate after you get the piston moving and you have the oil pan off so none of that stays in the engine anyways. Plus that is not getting pushed into the bearings and the engine is only being move a little and not at any speed just by hand.

[tom clisham]

If you don't know if you've got gas in the oil, just pull the oil cap & sniff. You'll know.

[tom clisham]

A good friend of mine bought a really nice KZ 750 for $300. Loved it & it looked great. This was last summer. he never checked or changed the oil.
Bearings fried one day on his way to work. Oil & gas in crankcase. Looked full in the sight glass.

[BA80]

You guys talk about wiping bearings and stuff. I'd like some details and maybe some symptoms of what this might be like.

As was stated gasoline is a solvent. Actually back in the day the only use for gasoline was for cleaning. The origin of dry cleaning. However, too many people blew themselves up and that ended and the internal combustion engine was invented and gasoline was a perfect fuel for that.

The bearings in an engine actually "float" on a film of oil when the engine is running. That is why oil pressure is supplied through the crankshaft to all the bearings. In a properly lubricated engine the bearings and crankshaft don't touch each other because of this coushion that is between them.

The vicosity of the oil is what provides that cushion. The gas breaks down the viscosity and makes it to thin to supply that cousion. When a bearing actually touches the steel of the crankshaft it causes wear and friction, if it touches a lot it causes a lot of wear and friction. Hence bearing failure.

Clear as mud?

[jimbyjimb]

Fuels or solvents in oil at very low RPM, like idle speed, can be used as a cleaning agent. The engine should not be revved during this period due to decreased lubrication. The solvent degrades varnishes and corrosion, in answer to one of your questions.

Why is it a big deal? Solvent thins your oil. Solvent also does the opposite of lubrication. While it might not seem like such a big deal at idle in your driveway it's going to be a huge one at 4500 RPM on the freeway, or better yet 7500 RPM on a hard shift. If you want your engine to last you want that oil as clean and viscous as it can be. The viscosity creates a thin barrier between wear surfaces, thin that out enough and you have metal on metal contact.

Do you want all the internal crud the solvent knocked loose running around between your bearings or plugging your filters? Nope. Do you want decreased lubrication on a high-performance, high-revving engine? Nope. Messing with oil viscosity will also effect how your clutch functions and potentially degrade friction matrial on the clutch. It can also effect heat dissapation since oil is the only cooling fluid these engines have.

[ViperRon]

Any gas is bad because it causes vaporization. Too much gas will thin oil causing loss of viscocity and wear of all parts but even a little can cause cavitation. http://en.wikipedia.org/wiki/Cavitation

http://scholar.google.com/scholar?q=...ed=0CBoQgQMwAA

I know this is all a little complicated but you asked why not gas. A simpler explaination is that tiny bubbles in the oil going at high speed threw the pump and arround the bearings cause pitting and fatigue of the metal. For the more experienced people here is the reason a failed bearing is not always smooth and has all those tears, pits, holes, and rips in it.

If you do not believe this put oil in a milk jug seal and shake it. Hey its still oil. Then put one tablespoon of gas in it seal and then shake it. See the bubbles.

[Bonz]

The KZ750 example in this thread is one of the few examples I can recall that is a result of a butt-load of gas in the oil based on the evidence.

I disagree with the adage "just take off the oil cap and smell if there is gas in the crankcase". Oil removes by products of combustion, change your oil and get it on your hands. You smell like gas. Period. Any oil in any crankcase I've ever smelled has smelled of gasoline.

I sent a sample of oil from my ZRX1200 to Blackstone last fall, the oil had 4010 miles on it. Testing showed 1% fuel in the oil (the bike is tuned very well, as is my XS), with an acceptable limit of 2%. So, it was under the limit to where it would start to raise an eyebromw. Blackstone said motorcycles for whatever reason, historically show some fuel in the oil. We are kidding ourselves if we think some gas in the oil is catastrphically harmful.

A cup of gas in a crankcase that holds 4 quarts, is 6.25% gas in the oil. Don't think that even 6.25% gas in the oil would defeat the oils capability to do it's job.

Now, a quart of gas along with 4 quarts of oil might be a different story, but if you are checking your sight glass, you already know where the oil level should be and would have an accurate reference as to excess gas in the oil.

I don't think the gasoline acting as a solvent will free up enough crud to ruin a motor, unless that motor was a mess to begin with and then the free roaming crud that the oil filter somehow would not filter out (?) is the least of that motor's concerns.

To play the devils advocate, why not start the engine up and ride around at low rpm and low load to evaporate the gasoiline out of the oil if you have determined there is excess gas in the oil from whatever reason?

Ok, let the games begin!

[BA80]

To play the devils advocate, why not start the engine up and ride around at low rpm and low load to evaporate the gasoiline out of the oil if you have determined there is excess gas in the oil from whatever reason?

It will evaporate but the damage is already done. The viscosity of the oil was ruined when the gas was in there.

You can't fix it.

[fredintoon]

And then there's 2-strokes. Oil injection or oil & gas mix or a combination of both, they all lubricate themselves with gas in their oil and do well on it.
Mind you, there ain't any of them got plain bearings, eh?

[Bonz]

Ahhh... Interesting... Kind of like scrambling eggs, eh? Can't make them a yolk and a white again, it's a one way street. I'm still not convinced this oil dilution is as bad in most cases as we've made it out to be.

How about this... If a bike has small amounts of gasoline ingested into the oil over a long time, wouldn't the oil be used up (thinned out) the same amount as if the total sum of those small amounts is dumped in at one time? What I am getting at here is the oil probably has a lot more capacity to deal with large amounts of fuel at once than we are giving it credit for. Otherwise, we are all running the equivalent of water at the end of an oil change interval, which we know is not the case. In most cases if the oil was analyzed, it would show there is plenty of service life left.

So, the carrying capacity of oil in terms of how much gas it can digest and evaporate or whatever over a change interval, or take on all at once, is the question as it relates to the oil losing viscosity, which is the ultimate problem as far as I can tell.

[motoman]

It will evaporate but the damage is already done. The viscosity of the oil was ruined when the gas was in there.

You can't fix it.

+1 what Greg said. Even the smallest amount.......bearing damage IS done......you just don't know it..........then wonder why at 70K a strange bearing noise/knocking occurs when the motor should have easily went over the 100K mark without issues. Ever see a bearing "wash out"? Any amount of fuel in oil will definitely get'r done.........

[Bonz]

If a bearing goes at 70k, when others have gone to 100k, that could be because the oil went too long between changes, the oil got overheated during a particularly hot summer ride, many reasons besides the oil was contaminated with gas can make it thin out and cause bearing damage. Or someone running the pee out of the engine, rpm wise, when that is never conducive to good engine life regardless of the oil's state of being.

Who else here on this forum have had undeniable bearing damage in one catastrophic failure that was because a post-mortem revealed gas flooding in the oil? Not saying it isn't a problem in the extreme, but in the event of a carb bowl or two emptying out into the crankcase, is that really gonna cause a problem?

With the knowledge as to the fact there is a problem with excess gas in the oil, there must be knowledge as to how much gas in the oil gets it to that point.

[natemoen]

No, we cant say for sure how much gas is too much, so I say again, why risk it. Oil is cheaper than engines, when in doubt change it out.

[Bonz]

I do agree when in real doubt, change it out.

So, what is real doubt? Not trying to keep the pot stirring, but at the same time, I am trying to keep the pot stirring!

Inquiring minds wanna know, instead of just asking the question and getting the same basic answer, I'll start looking around for info about how much is too much, film at 11 so to speak when I find something.