Marvel Mystery Oil in Fuel

So I generally add MMO in the recommended quantity (maybe a bit more if I haven’t used it in a while) to my gasoline. I like to think that it serves some purpose as a top lubricant even if it probably doesn’t make any difference.

I drove the car for a while (about 100 miles) and parked it at my house. Since I am the one who always drives around, I used my wife’s car so some of the wear could be shared on her vehicle (I am a poor engineering/medical student). I let the car sit for about three days. When I started it up, it took a little bit longer for the engine to catch as expected but then I heard a metal clank sound. It sounded exactly what you would expect to hear when a car drives over a sewer cover. I couldn’t tell if it came from my car or if someone actually did just run over a sewer cover behind me (my wife was on one of her talking sprees where you can’t even process the information as fast as she can ramble and so I am really not sure).

Now, assuming it was my car, what do you think that sound would be coming from? Do you think the Marvel Mystery Oil could have caused an autoignition (I have heard an autoignition before but it didn’t sound like it- autoignition tends to have a more dieseling kind of sound).

Thank you in advance,


I suspect the sound was the starter re-engaging the flywheel as it was still turning. I’ll be surprised if it does it on a regular basis.

Save your money for tuition, you’re probably wasting money putting it into your gas tank.

That was my bet too, I was hoping someone else was thinking the same thing. Now I can rest with ease and know it wasn’t just my own wishful thinking. Thank you.

If it saves my engine a bit of wear and maybe even prolongs the life of my fuel injectors just a little, it’s worth it. Besides, even a placebo is worth it to me, MMO is dirt cheap as it is.

Whatever made the “clank” it was not the Marvel Oil…Whether adding top oil to the gas offers any real benefit is a debate that has been going on for 90 years…it certainly does not hurt anything…

What happened when you immediately shut the car down and restarted it? Did you hear the sound on the second trial? You didn’t mention that in your post.

Engineering? Medical? Okay…

Undergraduate: Chemical/Pharmaceutical Engineering
Currently: Medical School

Glad to hear it. I thought it might be partially responsible for the atypical hard start. The issue has not resurfaced.

Did it happen only once?

MMO didn’t cause it. Continue using as recommended (dosage rate) if you so desire.

Using too much too (as in WAY TOO MUCH) often will soot up your plugs. The recommended dosages should be fine.