After seeing several mentions of Marvel Mystery Oil in different threads about vehicle maintenance and care, I'm curious about what the consensus thought is about this stuff.

Is it really something that is useful to add to one's fuel? If so, how much should be added to a tank of fuel and how often?

Don

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Laus Deo! <><

Prior to switching to 100% diesel power, I added a can to every tank in all my gassers...I can only attest to never having a valve or combustion chamber problem......Ben

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Cogito, ergo BOOM!...

It has a long list of uses, but I prefer SeaFoam to put in the gas/diesel tank.

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On the Oak Savannah

Many farmers seem to like Lucas fuel additive in higher mileage engines. I tried a couple gallons but don't know if it helped the longevity or not but I did drive my Nissan Titan for 260K miles.

I have heard so many "it's great" or "don't waste your money" opinions over the years, all depending on the particular problem at hand, that I don't know what to believe.

Been using MMO for many years, from cars, to bikes, to lawn mowers, to snowblowers, etc.
Throw in a bottle of Techron for gas at every change also.
Don’t know if it beneficial but never had an engine problem, and not expensive.

I don’t know about adding to fuel but my pistol bag has a small bottle of it and I use it often on auto pistols. I prefer something a bit thinner for revolvers.

Look on Wikipedia's discussion about MMO. I don't see anything magic there. Seems like it is mainly lube oil thinned by mineral spirits. Says there is no scientific evidence verifying claims made about its use.

MMO has a high cool factor. I still have a metal can sitting on a shelf. Nifty graphics and smells good too!
But... how does that old 20th century solvent and light oil technology help your motor, gun, etc.???
Seafoam is another product with mystique. It actually does help decarbonize engines.
But... so does just plain water.
Techron is in another category. Simplified down it is a modern detergent, I can vouch from multiple personal experiences, it is brilliant at dissolving gum and varnish in fuel systems.

I surmise it is like the ancient joke about the beatnik discovered in a pool of light on a dark night beating a street lamp post with drumsticks.

Asked why, he says it keeps the tigers away. Told there aren't any tigers around he replies, "Told ya so."

I don't use any snake oil treatments in my vehicles and they work fine for a long time. However, the additives may do no harm. I doubt there is much scientific-type credible evidence one way or the other, so these discussions continue forever. Use them if you like them.

I always thought Marvel Mystery Oil was at its best as a penetrant. It smells good.

Just like all those mystery medicines and cosmetics ads you see on TV.

I have never put SeaFoam or MMO in any tank of gas and I have the same good luck with my cars as the people that DO use the snakeoil stuff.

I started using Seafoam in the gas on my boats. I have a 1979 Eminrude that was given to me. Had to pick it up at the marine mechanic place as it had a new water pump put in. Other than 2 more WPs since it starts runs and needs so little maintenance...it seem's like the Energizer Bunny. Never use fuel with alcohol in my small engines chainsaws etc...little seafoam day before I take 'em out to cut in the splitters mowers Seafoam first. I used synthetic oil in a Datsun Pickup I had... it got terrible mileage Just the oil change and I had to reduce the 800 RPMs idle it picked up. Trans oil rear oil/grease and the truck picked up literally 8 MPG. just saying that sometimes things really do work. Don't know about MMO though. There's a guy on you tube that tests all these things. I watched his presentation on Seafoam a year or so ago

Once a product gains widespread acceptance it can coast on its name for generations.
E.g. WD-40, millions think it is a good penetrating oil or lubricant. It will do those jobs but rather poorly when compared to the real thing.

I had a friend that swore by MMO... but he only used it on his machine guns... his Ma deuce ran beautifully with the stuff.... never used it in vehicles of any kind..

I use Seafoam MMO and StaBil for different things. Usually outboard motors. I run some Seafoam through my ATVs and UTVs yearly. MMO is nice to coat inside of a gas tank that will be empty for a while

I had a car a few years ago with a well known issue of the gas gauge not reading full even if you filled it to overflowing. Which is not a good thing.

A dose of MMO would solve the issue, for several fill ups anyway. Apparently the float or sensor that measured the fuel level would get sticky and the solvent or lubrication properties of the MMO would free it up. And before you blame the fuel, all I ever used in that car was 91 octane top tier fuel. So MMO does definitely have some beneficial applications.

I use Stabil in the fuel for my snowblower, I also only use top tier fuel in it and at the end of the season I add an ounce to the gas tank and then run it dry. I figure the MMO helps clean the carb jets and float. It is inexpensive and works but isn't a panacea for serious mechanical issues. It's just a mild solvent and lube.

I collect old outboard motors. Seventy Three are hanging on the walls in my museum (the wife's terminology) as of this writing. I run E10 in everything. Fantastic stuff....keeps the internals clean. A little Stabil in the Fall in a full tank of gas. Nothing else.

My Classic Lyman sports a 1953 Evinrude Big Twin. The fuel lines have been replaced with alcohol compatible ones, and the lacquered cork float in the gas tank was replaced with a neoprene rubber stopper. Fresh water usage, so I can get 8-10 years on a water pump impeller.



I shoulda been a snakeoil salesman.....coulda made a lota money.

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The only additive I use is Mechanic in a Bottle, which goes in all my weed eaters, chainsaws, blowers and gator. Other than that, only ethanol-free gas in my vehicles. I overdo it on oil/filter changes but consider that a safe habit.

I had an old locking gas cap that I inherited from my Uncle. Probably dated to the 1940's. When the gas crisis of 1973 happened I put it on my wife's car because she parked in a lot at her workplace with no security. Apparently, the seal was shut solid. Good fuel pump on that old Ford. When the car finally quit it had sucked the tank into a concave mess. It would only hold about 5 gal. Had to fillerup every day.....LOL.

Dad used to swear by draining the tanks for Winter so I did the same. Then several times I had carb problems in the Spring. The last 25+ years of leaving my engines full of stabilized fuel has shown no problems at all.

All the hullabaloo about alcohol gas is due to moisture in the tank. A little bit and the alcohol fixes it. A LOT and you would have trouble with even E0. The secret is a full tank and dry indoor storage.

I worked for my Uncle on his ranch back in the 50s. He bought MMO by the gallon and used it in everything. I only used it once in a 66 Pontiac 421 with sticking lifters. After a quart in the gas my problem went away and never came back. Never saw the need for regular use as long as every thing was working.

I studied fuels and lubricants in my undergraduate studies. I also designed and developed modern spark ignition engines. In my opinion, there is no such thing as a mechanic in a can or bottle. It is true that gasoline oxidizes and becomes “sour”, especially in the presence of yellow metal. Stabil inhibits this aging process and increases the shelf life of gasoline. Another factor is the corrosive effects of alcohol in gasoline. Considerable engineering went into the design of fuel delivery and metering systems to allay these concerns. In simple terms, manufacturers design, develop, and rigorously test to ensure 120,000 miles/7years of emissions compliance. After that period, it’s anyone’s guess what will happen. Disclaimer: I’ve been retired for ~ 20 years!

PS - exhaust gas oxygen sensors don’t like chemicals like silicon. They get poisoned and drive the calibration very lean. I’d be careful with what I put in the gas tank.

MMO in the gas tank says on the can: 4oz per 10 gallons. That's what I use in wet winter weather. My '91 E350 with 460 ci injected still runs at 432,xxx miles; No rattle, no smoke, no complaints.

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"Don't Give Up the Ship"

I don't see much point in it in an otherwise well maintained engine.
On the other hand, if your reviving something that's been fermenting in the back 40 for a few years, such things start making sense

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it just needs more voltage

Patchouli Oil since the 60's for me.
A lil dab will do ya.

Do NOT use it in diesel fuel! Since sulfur was removed from diesel fuel there is less lubricity and I can tell you from personal experience that with a Bosch VP44 injection pump that is used in a 2002 dodge ram with the 5.9 cummins, MMO is NOT a lubricant, it is a solvent! I have however used it on gasoline engines with great results.

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NRA Endowment member

I have a long history with Marvel Mystery Oil . I used to buy it in 5 gal cans . I had tractors , front end loaders and a dozer . It kept my motors cooler working in the hot sun in southern Az . Without they ran much hotter .
My fiance's 06 Chrysler Town and Country at about 150K miles starting using oil , a lot of oil between oil changes . After a couple of tanks of gas mixed with MMO , the oil comsumption between oil changes dropped to zero . I use it to clean my firearms . Yes , I MMO stands well with me . Regards Paul

I used to get stuck valves in my 1948 Indian motorcycle (air cooled side valve engine) until I threw in a little MMO in the gas tank every so often. Never had a stuck valve since.

Speaking of motorcycles , I have in the past rebuilt antique Harley's . After rebuilding the engines and transmissions , MMO was a " god send " . The transmissions shifted sooooo much smoother just adding a couple of ounces of MMO . Added to the fuel , it kept them clean and running cooler . Remember I'm talking about southern Az in the summer time . Regards Paul

I worked for a Pneumatic tool company decades ago and they put a small bottle of a special Airetool oil in with every tool shipped. It was MMO.

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Sceva
OGCA SWCA NRA

Nice collection.
I have a old blue & yellow, 5hp , Good Year in my garage, that my father used back in the 60's.

Memories.

While I no longer use MMO in our cars and trucks, I still use it around the house and workshop as a general lubrication and gunk remover. I LOVE the smell! Although I have never used it on guns I don't see any reason why it could not be used. It is sort of a CLP.

I still have an original metal quart container that I pour new stuff into. Never liked the plastic - lol. I also have two old oilers that are filled with the MMO for handy use.

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I have never used it on a motor. But I have found it to be a quick penetrating oil and rust remover for guns and tools.

It is especially useful for cleaning rifle barrels that have shot a lot of molybdenum coated bullets.

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6/23/2022

In my experience it has been good stuff. Also a good gun cleaning solvent.

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Can my S&W Mdl 10 shoot +P

Me and a buddy bought a '52 Buick Special for parts. I drove it home, but it had noisy lifters. My dad, who worked on straight eight Buicks for years, looked it over. It was missing the oil filter housing. I had an extra one and we put it on the engine. Then my dad had me buy a quart of MMO. We put that in the engine, cranked it up and after a few minutes, the "ticking" went away.

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John 3:16
WAR EAGLE!

All that Mystery Oil type stuff may have worked well in old carbureted engines. But new car engines with all the sensors and computer controlled fuel injection, not so much.

Just buy good gas.

I know folks who swore by using Marvels. Others who love Seafoam. I used Lucas in my diesel rig and had a noticeable increase in fuel mileage. '14 F350 with a 6.8 (loved that engine!).

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Even older, even crankier....

All I have to add is that I would never use anything that could create residue in a direct inject engine

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Pete
I ain't no fortunate son

Here is one of many BEST OF articles
Kinda like Best gun cleaners

The 10 Best
Just a moment...

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Still Running Against the Wind

Crude, older engines from the early-mid 20th century did seem to respond to the so-called 'top oils'.

With our first fuel injected car my wife still had her stubborn habit of driving miles out of her way to imagine she would save a few pennies on the cheapest gas. Unsurprisingly it started running rough. After numerous battles she finally started buying fuel at better (Chevron, Texaco, etc.) gas stations. Less than two tanks later it was running smooth again.

My love affair with Techron began when I had a couple outboard engines that were notorious for the carburetors plugging up during the winter layup even though they had been drained.
A lot of guys with that model spent hundreds and hundreds of dollars at dealerships getting them cleaned, rebuilt and replaced.
Getting a strong dose of Techron additive & gas into the gummed-up fuel passages and letting it sit for a full day worked every time. I tried quite a few other brands of fuel additives, even Seafoam, without success.

Pick up a can of Kroil, it really is a better product. I was amazed when I was introduced to it back in the '80s.

There is a lot of “weird” info in this thread. Some good too.
It is just not possible to talk about all additives at once, they do far too many different things.
MMO is not something that I would ever use as a fuel additive, for any reason. I do not believe any of the “I just add it and it works better” comments, but it is their money.
Stabil is different, and it most certainly does increase the life of gasoline, which in turn can reduce carb, line, and tank problems if used properly. A has been alluded to, I still drain my tanks “and” carb if sitting for more than 5 or 6 months, often less. And if you’re not going to drain your carb, just dont’ worry about it! You’ll rebuild several carbs before you have a tank problem as rule.
I strongly feel (as a mechanic, engineer, and homesteader) that if folks put a small fraction of energy into proper storage, handing, operating, and maintenance practices, they’d find that the vast majority of these products are witch’s brew.
That said, many of them, like MMO, do have practical use! It really is just a diluted lubricant, and once in awhile that’s all you need! Especially if it’s sitting on the shelf.
Personally, I have “exactly” one use for it, and that is out of habit. In the early 70’s I learned to fill a frozen engine block with MMO and let it sit for a week, to try to break’er free. It does work, but often takes more than a week, a few other things, and a lot of MMO! Kroil probably works better, but flows to free in some cases. It’s just a lubricant!

Jim that’s a great collection. Did you restore all of them? Do they all run? I suddenly don’t feel so bad about the 5 or 6 in my garage. What’s your favorite in the collection? My favorite is a 1964 British Seagull.

We used it in the dash pots of SU carbs on British cars a lot…

Here's a 1948 Goodyear 5 HP...

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I used nothing but top tier 91 octane gas in my car.
MMO solved the wonky fuel gauge reading every time I added some to the tank. Not permanently, but at least for the next 3 or 4 tanks full and then the gauge would start reading less than full by about 1/4 of a tank. Another dose of MMO and the problem was again (temporarily) solved. A whole lot cheaper than dropping the fuel tank and replacing the sensor no ?

I guess some won't believe the anecdotal evidence until they see it for themselves.

Sometimes band-aids are good. Certainly cheaper and faster.
IMHO, its better to attack the root cause. Most people don't have gas gauge problems. What caused yours?

My dad flew his own Cessna before I was born. At that time, MMO was the only additive allowed to be used in aircraft engines. If compression was down on an annual inspection, the mechanic would put some MMO in each cylinder, run the engine, and retest. If it passed, it was good, if not, the owner got rings, cylinders, whatever as required.

Like most additives, people mistakenly believe you dump a can in the tank and it miraculously solves the problem. It doesn't except for maybe the most minor ones. They take time and several doses over several tanks to take effect. Most work better as a preventative, preventing varnish and gunk before it becomes a problem.

MMO is also good for keeping the internals of an engine nearly spotless. Add a can, usually 20% of oil capacity, to the oil with your oil change--per MMO instructions. Some think you only add it 500 or so miles before an oil change, and that will help clean sludge, but there is nothing wrong with using it full time. I use it in my gas and oil, and I've never had an oil/fuel related issue with any of my vehicles.

It's been around for over 100 years and I've never met anyone who has had issues with using it. I've put it in vehicles and lawn equipment. Of course regular maintenance (oil and filter changes, etc.) does more miracles than an additive ever will though.

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Ephesians 6 (Armor of God)