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Marvel Mystery Oil In Spark Plug Hole - Myth or Fact ?

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mgbtf Avatar
mgbtf Silver Member Dave Kalp
Fort Wayne, Indiana, USA   USA
1969 MG MGC GT
1980 MG MGB
At a recent Cars & Coffee I overheard two classic car owners discussing winter storage. They both said they put a small amount of Marvel Mystery Oil down each spark plug hole for winter storage. I have never heard of this. Has anyone here ever heard/done this? If so why would one do this? What is MMO?

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Chalky Avatar
Chalky David White
Coventry, Warwickshire, UK   GBR
I leave the car for months without adding anything into the cylinders and it always starts and runs without problems. I vote for myth.

nickj Avatar
nickj Gold Member Nick Jenkins
Novato, Marin Co, CA, USA   USA
1970 MG MGB GT
1972 MG MGB
A lot of people are big fans of MMO. It's probably the name. Sounds better than '3-in-1 oil'. Squirting little in the cylinders probably doesn't have any negative effects.

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Rancarl Avatar
Rancarl Gold Member Randall Carlson
Fairfield, California, USA   USA
1971 MG MGB "B Minus"
Dave, Marvel Mystery Oil is basically snake oil. It is touted as a fix-all for automotive problems, but it's only 20 weight oil with some coloring put in it for "mystery." It is not harmful if properly used. Putting a teaspoon down the spark plug hole before storage and giving the engine a couple of revolutions isn't a bad idea. Engine oil would do just as well. Leave the spark plugs loose so that you can use the starter to spin up some oil pressure before you fire it up in March. Oh, that assumes that you've put a trickle charger on the battery over the winter.

33EJB Avatar
33EJB Tim C
LS, Eastern Ontario, Canada   CAN
1969 MG MGB
I used to squirt a little regular (non-mystery) engine oil in each cylinder, then rotate the engine a few times on the starter to coat the cylinder walls to prevent corrosion. It was a thing most old car people seemed to do out of habit.

I concluded long ago that it wasn't necessary for a storage period of several months. No harm, but no benefit either.

I'd probably do it if the car were to be sitting for a year or more, as much out of superstition as anything else. Couldn't hurt in that case, right?

benhutcherson Avatar
benhutcherson Gold Member Ben Hutcherson
Louisville/Frankfort, Kentucky, USA   USA
1970 MG MGB
As said, MMO is basically a light mineral oil(somewhere around SAE20) with red dye and a small amount of oil of wintergreen.

I often use it for things like doing wet compression tests. Its about the right weight, will burn out of the cylinder freely, and is a lot less expensive than 3-in-1.

Some folks use it for their carb dashpots-I personally prefer something MUCH thicker.

I often hear it referenced for "waking up" an engine that hasn't run in a while with the idea being that it's thin enough to get in and unstick rings and the like.

I suppose the idea of putting it in before storage is that it would keep this from happening, but I doubt that would happen over the course of a few months. I don't think you'd hurt anything, but I don't know that you would help it either.

Rod H. Avatar
Amity, Oregon, USA   USA
1964 MG MGB
1968 MG MGB GT
MMO also has some solvent and a few chemical additives to soften carbon deposits, and corrosion inhibitors.



I can't understand why people are frightened of new ideas. I'm frightened of the old ones. John Cage

'63 MGB
'68 MGBGT
'80 VW Vanagon Kombi
'09 Mazda 3 with 5 speed manual

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J Baz Avatar
J Baz Silver Member Jerard Basmagy
Middletown, New Jersey, USA   USA
I use to fog out a 318 Chrysler marine engine with it then a little in each cylinder when putting the boat to sleep. I never stored without it so I don't know if it really made a difference but it was peace of mind.



jb

Too soon we get old, too late we get smart!



Edited 1 time(s). Last edit at 2017-11-26 02:22 PM by J Baz.

Basil Adams Avatar
About 12 miles from Sears Point, CA, USA   USA
Marvel Mystery Oil has been around for almost 100 years (1923). It's a combination of mineral oil and mineral spirits and trace amounts of an anti-wear agent, a chemical that softens carbon depisits and an agent that keeps it from breaking down in high heat. The reason people put it in the spark plug holes for storage is that it will drip down to the rings and wick around the ring to keep the ring from corroding to the block. A little bit of automatic transmission fluid will do the same thing. But Marvel looks good on the shelf and it has a great name and you can use it in your dashpots (ATF too). Basil



Basil C. Adams
1956 MGA Coupe (Show Car)
1957 MGA Roadster (Driver)
1958 MGA Coupe (Racecar)
1959 MGA Coupe (unrestored)
1960 MGA Coupe (unrestored)
1960 MGA Roadster (Driver)
MKIII Elva Courier (E1056)
1967 427 Cobra
1972 Alfa Romeo Montreal
A coupla late MGBs
1960 Austin Healy BN7
More Cars than Brains

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RAY 67 TOURER Avatar
RAY 67 TOURER Ray Marloff
Fort Bragg, CA, USA   USA
1967 MG MGB "My Girl"
As Jerard stated, "fogging" an engine, before several months of storage, protects it from moisture. Coming from the same area that he did, I worked in two marinas where fogging an engine before storage was common practice. I had over two hundred boat engines under my care and running the engines and fogging them, with Mercruiser products, was the norm. We would run the engines until they stalled. Then, we would tape off the flame arrestors, no air filter required on a boat because there's no dust on open water, remove the stern drives for winterizing and take the batteries inside for storage. Every single engine would fire off first time in the Spring. Is it a necessary step in winterization? All I know is that it worked. Enough so that I did it to every boat that I owned as well. RAY

stuntflyr Avatar
stuntflyr Chris McMillin
Catalina, Foothills, USA   USA
My parents had a Franklin engined Stinson Station Wagon that was designed for 70 octane gasoline with very little lead, so now that only 100LL is available with way more lead than these low compression engines combustion heat can properly burn Marvel Mystery Oil at 4 oz per 10 gallons of gas kept the valve stems and guides clean and moving freely. Never had a cylinder problem with it where I knew others that stuck valves without the MMO additive.
Chris...

Gerry Avatar
Gerry Gold Member Gerry Masterman
Prairieville, Louisiana, USA   USA
I believe in it. Are there better things? Probably. Are there worse things? Most definitely. Is it a cure all for everything that ails your engine? Not a chance. Like STP, I have had good results with it through the years for multiple purposes.

FWIW https://en.wikipedia.org/wiki/Marvel_Mystery_Oil

RAY 67 TOURER Avatar
RAY 67 TOURER Ray Marloff
Fort Bragg, CA, USA   USA
1967 MG MGB "My Girl"
STP = Stay Together Please. RAY

Gerry Avatar
Gerry Gold Member Gerry Masterman
Prairieville, Louisiana, USA   USA
Years ago I was involved in making solder in shotgun choke tubes. They were made by forcing a piece of steel tube into a die with a tapered ram. We tried more than a few lubes to keep the blank from becoming stuck in the die/tube. Oil did not work, several greases including moly did not work. Straight STP did not work. I tried some engine assembly paste that I used for years before engine assembly paste was readily available. My mix was 50/50 STP and 30WT oil. This combo worked like a dream where either one of it's components alone failed miserably. FWIW

As for the MMO, I have used it to free up stuck engines. Takes time. That's not to say that other fluids would not have worked as well, just that it worked. Diesel in the bores worked, too. Diesel make a very good penetrating fluid-it creeps into gaps other oil does not go.

In reply to # 3634598 by RAY 67 TOURER STP = Stay Together Please. RAY

stuntflyr Avatar
stuntflyr Chris McMillin
Catalina, Foothills, USA   USA
I use 50/50% STP and 50 wt engine oil for assembly lube!
Chris...

In reply to # 3634602 by Gerry Years ago I was involved in making solder in shotgun choke tubes. They were made by forcing a piece of steel tube into a die with a tapered ram. We tried more than a few lubes to keep the blank from becoming stuck in the die/tube. Oil did not work, several greases including moly did not work. Straight STP did not work. I tried some engine assembly paste that I used for years before engine assembly paste was readily available. My mix was 50/50 STP and 30WT oil. This combo worked like a dream where either one of it's components alone failed miserably. FWIW

As for the MMO, I have used it to free up stuck engines. Takes time. That's not to say that other fluids would not have worked as well, just that it worked. Diesel in the bores worked, too. Diesel make a very good penetrating fluid-it creeps into gaps other oil does not go.

In reply to # 3634598 by RAY 67 TOURER STP = Stay Together Please. RAY

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