Marvel Mystery Oil

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I bought a new 92’ GMC with the 4.3L V-6 that had a serious knock when starting that would immediately go away. Wouldn’t do it every time. I talked to a GM mechanic and he told me when that engine is cut off that it stops in 1 of 3 positions and to mark the crankshaft pulley and see if it did it only in one position. I did and it did. He said it was a lifter bleeding down and to try the MMO. It completely cured the problem and was still running great at 150K miles when I traded it.
Cured the knock.
Had you used HPL Engine Cleaner or Rislone Engine Treatment you may have had the same or better experience.
 
To its credit, there are a lot of claims of benefit but no harm I've read about (except the random comment on this page). I dunno...
A general observation:

Anecdotal statements are just that. Anecdotal: not necessarily true or reliable, because based on personal accounts rather than facts or research.

Now if you totally reject technical information, such as organic chemistry, then no amount of technical information is going to rise above anecdotal statements in the area of "convincing." ;)
 
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A general observation:

Anecdotal statements are just that. Anecdotal: not necessarily true or reliable, because based on personal accounts rather than facts or research.

Now if you totally reject technical information, such as organic chemistry, then no amount of technical information is going to rise above anecdotal statements in the area of "convincing."
I totally agree. The amount of anecdotal information on this forum is bizarre. "I put so and so in my engine and it...... hasn't blown up yet... so it's good stuff!" No, that's not how experimentation works. 😁

My comment was due to someone saying it would cause harm, which I had not seen mentioned before by anyone other than those that tend to generalize. I was wondering if there was any negative anecdotal evidence to go along with the loads of positive.
 
Many years ago, I used it in the fuel of an older vehicle with good results. I have used it to clean dirty carburetors and fuel lines on older lawnmower engines (B&S and Tecumseh), also with good results.

I have never added it to the oil of any vehicle or small engine.
 
I"ve used MMO since the early 80's as a fuel additive about every 4 tank fill ups, and can say I have never had an fuel injector, fuel pump, or any fuel related problem with it. Is that proof, no but that's my experience with their product. However I never add MMO to my engine oil.
 
I bought a new 92’ GMC with the 4.3L V-6 that had a serious knock when starting that would immediately go away. Wouldn’t do it every time. I talked to a GM mechanic and he told me when that engine is cut off that it stops in 1 of 3 positions and to mark the crankshaft pulley and see if it did it only in one position. I did and it did. He said it was a lifter bleeding down and to try the MMO. It completely cured the problem and was still running great at 150K miles when I traded it.
Cured the knock.
It's beyond me to understand how on a new vehicle with a lifter bleeding down that MMO could fix that ? Was it instantly fixed ?
 
I"ve used MMO since the early 80's as a fuel additive about every 4 tank fill ups, and can say I have never had an fuel injector, fuel pump, or any fuel related problem with it. Is that proof, no but that's my experience with their product. However I never add MMO to my engine oil.
Okay sure but I’ve never used MMO and I also have not had an injector, fuel pump or fuel related problem even on my ancient vehicles.
 
It's beyond me to understand how on a new vehicle with a lifter bleeding down that MMO could fix that ? Was it instantly fixed ?
Yes it was. Just giving my experience with it. Not giving it a thumbs up or down. It worked. Possibly could have used something else and had the same results. I have no gain in whether anyone uses it or not.
 
MMO came out in 1923, almost 100 years ago. It has been a good seller ever since. Most products that don't work, or have a limited purpose don't last that long. Especially in the engine oil / fuel additive market. This one has.

And it has managed to do so without a major, expensive advertising blitz, that normally accompany so many of these products. In fact it was on the market for over 20 years before TV even existed. So I think it's fair to say it has some satisfied customers along the way.
 
MMO came out in 1923, almost 100 years ago. It has been a good seller ever since. Most products that don't work, or have a limited purpose don't last that long. Especially in the engine oil / fuel additive market. This one has.

And it has managed to do so without a major, expensive advertising blitz, that normally accompany so many of these products. In fact it was on the market for over 20 years before TV even existed. So I think it's fair to say it has some satisfied customers along the way.

99% of those "satisfied customers" don't do UOAs, pull valve covers to verify results, flow test injectors before and after, run a bore scope into the cylinders, etc... The ones that do aren't using MMO.

It's still on the shelf for the same reason McDonalds is still in business. People keep buying it. "I eat 3 double qtr pounders with fries every day and haven't had a heart attack so it must be good for me." That doesn't sound as logical, does it? There's a lot of junk products on shelf that keep selling because gullible people believe a marketing label over scientific data.
 
99% of those "satisfied customers" don't do UOAs, pull valve covers to verify results, flow test injectors before and after, run a bore scope into the cylinders, etc...

So what? Perhaps they were simply satisfied with the results. And the product achieved their goal. Which is exactly what some here have stated.

If you screw in a light bulb and it works, are you going to take it apart to find out why?
 
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