Not so marvelous

[mikenixon]

I just this minute finished communicating with a GL1000 carburetor customer whose carbs are on my bench and which I suspected were victims of the use of Marvel Mystery Oil. He confirmed my diagnosis. How could I tell? The vacuum chambers accumulate an tenacious, inky black slime inside. Only three things cause this and it's easy to narrow it down. More than 90 percent of the time it's Marvel Mystery Oil.

Adding mostly innocuous agents to engine oil has been a popular if officially unsanctioned pastime for generations while proving to do little harm. Or good. But such is not the case with things added to *gasoline*, as with the Marvel. It really isn't a good idea to monkey with your fuel, on many levels. And if ever there was a "snake oil", that is, something made of incredibly basic and virtually inert ingredients, and about which no substantiated benefit is known (and in the case of MMO, some harm, both observed and documented), Marvel Mystery Oil is it. Like bolt-on fuel mileage improvers, engine rebuilder in a can, and those odd, quaintly historic 1930s-era electromagnetic medical wonder "cures", Marvel Mystery Oil is the stuff of whimsy. Know what that stuff is? Baby oil. Yup. Some 70 percent mineral oil. So what? Well, that alone should give pause. But maybe you have to be a mechanic to understand.

Any first semester mechanics school student knows that adding almost anything to fuel is unwise and even in the best cases, such as in the legitimate use of fuel stabilizers, must be done carefully. But in the case of adding *oil* to fuel there really is no debate among professionals. Its a no-brainer. Don't. Oil in the combustion chamber slows the flame, and is a sure recipe for detonation. That's why blown head gaskets on some engines frequently result in engine damage: the oil entering the combustion chamber results in destructive knock. Additionally, oil in the combustion chamber also results in excessive carbon buildup on the valves, something you really want to avoid in Honda engines due to their already having valve durability problems. Deliberately putting oil into your cylinder is a really bad idea.

Marvel indeed.

[77Gowing]

Good article as usual.
One thing troubles me. Healthy engines do consume a bit of engine oil else they would not survive for long. In the emission measurement game there are called wet particulates and dry particulates to differentiate from oil Ash and fuel Ash respectively. Naturally a little oil consumption is normal, but not so in extremes where valve seals and rings have degraded. So a sweeping generalization that burning oil is bad can be a little misleading. But I get it that relatively high oil consumption affects the flame.
I personally never believed in MMO, mainly because all I hear is testimonials with no science to back it up. In research we as a rule avoided proposals that were all testimonial justifications with no technical details of explanation. Testimonials are simply just opinions and everyone has one. Remember the "Tornado" air inlet devise that "even you dear old Gramma could install in her car."
Worked in propulsion research for 30 yrs and we were inundated with all sorts of wackie ideas and gadgets that were backed up soley on testimonials and no scientific data.
OK Mike you put me on my soap box, it's late and I better step off of it now.
Great article though.

[eades473]

If I remember correctly a well know carb rebuilder once advised to use MMO to keep carb parts lubricated, I have been using it but not as often as was recommended, usually every other fill up. No other additives recommended for helping the carbs? I also remember a recommendation to use Marine Stabil but have never used it. Thanks for the info, sometimes a little information is too much!

[mikenixon]

Good article as usual.
One thing troubles me. Healthy engines do consume a bit of engine oil else they would not survive for long. In the emission measurement game there are called wet particulates and dry particulates to differentiate from oil Ash and fuel Ash respectively. Naturally a little oil consumption is normal, but not so in extremes where valve seals and rings have degraded. So a sweeping generalization that burning oil is bad can be a little misleading. But I get it that relatively high oil consumption affects the flame.
I personally never believed in MMO, mainly because all I hear is testimonials with no science to back it up. In research we as a rule avoided proposals that were all testimonial justifications with no technical details of explanation. Testimonials are simply just opinions and everyone has one. Remember the "Tornado" air inlet devise that "even you dear old Gramma could install in her car."
Worked in propulsion research for 30 yrs and we were inundated with all sorts of wackie ideas and gadgets that were backed up soley on testimonials and no scientific data.
OK Mike you put me on my soap box, it's late and I better step off of it now.
Great article though.

Thanks Gowing. It is interesting to observe how much oil residue is visible when ignition failures reveal left over oil in the combustion chamber.

[mikenixon]

If I remember correctly a well know carb rebuilder once advised to use MMO to keep carb parts lubricated, I have been using it but not as often as was recommended, usually every other fill up. No other additives recommended for helping the carbs? I also remember a recommendation to use Marine Stabil but have never used it. Thanks for the info, sometimes a little information is too much!

I know whom you speak of. Carb internal parts do not need lubrication and in fact suffer from it. As for Sta-Bil, a completely different thing with known, observable and documented benefits.

[eades473]

So am I doomed or if I quit using the MMO and switch to marine Stabil will the carbs be ok? seems thy work fine now, 2-3 years on last rebuild by the previously mentioned rebuilder. Thanks for the info!

[mikenixon]

So am I doomed or if I quit using the MMO and switch to marine Stabil will the carbs be ok? seems thy work fine now, 2-3 years on last rebuild by the previously mentioned rebuilder. Thanks for the info!

The two things are not related. Sta-Bil (red) is legitimately marketed as, and is demonstrably very successful as, a fuel oxidation reducer guaranteed to work for up to one year. Marvel Mystery Oil as far as I know is not promoted as a fuel stabilizer. If viewed as one that is unfortunate. I would cease using the Marvel if looking for any benefit at all, and if wanting to avoid its drawbacks.

[rcmatt007]

helpful to know....

[chewy999]

As always an informative piece from someone that commands respect. I suppose one way of looking at it is that fuel and oil companies spends millions on developing their products, so why add anything else.

[mikenixon]

You may be interested to know that the small aircraft guys are quite a ways ahead of us in understanding on fuel additives. It seems small airplane engines, because they are, to speak plainly, very low tech, have slanderously short lifetimes, with nearly all the trouble centered around valve issues, mostly sticking valves. For this reason, airplane people have been fooling with snake oils for quite a while, and the combined intelligence on this is pretty amazing. While one or two substances are still unknowns (i.e. no proof they are either good or bad) Marvel Mystery Oil on the other hand has for some time been put to rest, relegated to myth status by the clear majority. So much so that Lycoming has seen fit to issue at least two bulletins on the stuff.

[rcmatt007]

I have always suggested MMO is best over ice

[mikenixon]

I have always suggested MMO is best over ice

Might as well....

[77Gowing]

I have always suggested MMO is best over ice

Might as well....

Rather drink colonoscopy prep over the rocks.

[mikenixon]

I have always suggested MMO is best over ice

Might as well....

Rather drink colonoscopy prep over the rocks.

Har har! Now *that* is nasty!

[Rednaxs60]

You may be interested to know that the small aircraft guys are quite a ways ahead of us in understanding on fuel additives. It seems small airplane engines, because they are, to speak plainly, very low tech, have slanderously short lifetimes, with nearly all the trouble centered around valve issues, mostly sticking valves. For this reason, airplane people have been fooling with snake oils for quite a while, and the combined intelligence on this is pretty amazing. While one or two substances are still unknowns (i.e. no proof they are either good or bad) Marvel Mystery Oil on the other hand has for some time been put to rest, relegated to myth status by the clear majority. So much so that Lycoming has seen fit to issue at least two bulletins on the stuff.

Valves, specifically exhaust valves, are generally the issue with engine low compression, far sooner than piston rings. Did a leak down test on my 1200 and the exhaust valves on all four cylinders were flowing air quite well. Have the heads off for a valve lapping.

It takes a lot of time and research to get a good understanding on what is good and not so good. It is difficult to get beyond the "always done that" mindset to change habits.

Cheers