Marvel Mystery Oil? Harmful? Snake oil? or legit?

I have heard this tranny-like fluid has detergents that can clean valves.
I don’t mind pissing $6 on cleaning some valves by adding 1Q to my next oil change, but can it do any damage?
It seems like it gets good reviews, and my cars don’t have valve issues, but why the heck not?
Any huge reason to avoid it? I figure I’ll drive 500 miles with it before the next oil change.


Here’s my experience with Marvel mystery oil

If your lifter’s gummed up, it can sometimes help

If the lifter’s collapsed, it won’t do anything

It is not harmful

Worst case scenario . . . the problem doesn’t get resolved

More advice . . . if you have valve noise, check if you have adjustable valves or hydraulic

If you have adjustable valves, and they’re out of adjustment, adjust them. Marvel won’t help

Transmission fluid is just straight 10 weight oil with a higher detergent contant. So adding some to the engine oil could remove gum and varnish that can cause lifters to stick.


Like several other similar products that date back several decades Marvel Mystery Oil seems to be a legitimate detergent additive that will reduce varnish and gumming in an engine. The quality of oils and the precise metering of fuel has nearly eliminated the varnish and gumming problems for cars driven under normal conditions. Cars driven on short trips and often shut off before ever heating the oil to 180*F might still develop such problems and MMO might be beneficial. But it might not be any more beneficial than a quart of ATF.

In. This day and age, the best thing about Marvel Mystery Oil, is it’s name. Has a nice ring to it and a lot of followers. You can do better, you can do worse. The best thing you can say about any additive is, first, do no harm. For that reason alone, MMO has gained a lot of support.

"It seems like it gets good reviews, and my cars don't have valve issues, but why the heck not?"

Why piss away $6 to fix a problem that is not there?

Correction-it CAN’T clean valves, they’re in the intake tract. They don’t contact the oil. It can (maybe) help with noisy hydraulic valve lifters.

But no need to do it if there’s no problem. All makers specifically advise against using additives.

It seems like it gets good reviews, and my cars don't have valve issues, but why the heck not?

So does Slick-50.

It’s like looking for a cure for a problem that doesn’t exist. If it’s only $6 and you need to give it away, times 10 and give it to charity. You’ll feel better. As that’s the only results you’ll see anyway.

I’ve got a friend with a Mazda rotary that gets stuck apex seals… a LOT… and Marvel is the only thing that clears up the oil smoking. I can attest it works for that.

Looks like it’s simply paint thinner, which is a legitimate cleaner. I bet adding some gasoline or ATF to your oil would also clean the valves.

Didn’t you read what Texases stated earlier?
If you want to clean your valves, you need to introduce an appropriate solvent into the induction system. Putting MMO or other additives into the crankcase oil will have absolutely no effect on any crud that might have built up on the valves.

…and…unless you have a death wish for your engine, I suggest that you avoid putting gasoline into the crankcase.

Have a 2000 Jeep Wrangler, 4.0, 240K Miles, manual transmission. (daily driver) Approximately 5 years ago, I upgraded both differentials to 456 gears, lifted 2 and a half inches, and put 12 inch wide 33s on it. I put all the miles on it myself except 25K. It has been my farm tractor, tow truck, and bulldozer. I have used MMO since I have owned it. I have kept up with normal maintenance. The only thing has ever gone wrong with it is 2 each water pumps. Prior to this I had both a 92 Dodge Dakota (4cyl) and a 96 Dodge Dakota (V6), both manuals. I used MMO with both with semi synthetic oils. Both I put over 200K. No tick in any of these vehicles. I have changed oil regularly on all these vehicles. An oil change with MMO kept the oil clean (not Black) for up to a week with normal driving (approximately 100 to 150 miles) and that’s all that I have to say about that

Huh, after five years???

Maybe you folks ought to find a different term though. I for one am tired of the “snake oil” term and looks like I really should try to find some for my joints.

First, There Really Is Such a Thing as Snake Oil

It has been used as a pain remedy for hundreds of years.

The original snake oil came from Chinese water snakes and was used in China as a treatment for arthritis, bursitis, and other joint pains. It is believed to have been brought to North America during the Gold Rush in the mid-1800s. The oil, which was really fat that was taken from the snakes, was actually studied in the 1980s and found to be full of omega-3 fatty acids. Of course, we know omega-3 fatty acids are prescribed today to reduce inflammation (which can lead to arthritis), reduce blood pressure and more.

Other studies have been reported as well. In Japan, snake oil was rendered from Erabu sea snakes, which are the same species as the Chinese water snake, and determined that the Omega-3s were present in their fat, too. In 2007, Japanese researchers reported on a study in mice that showed mice had improved abilities when ingesting snake oil rendered from those Erabu snakes over those mice who were fed only lard.

3 generations of my family have usedused /use it. Clean engines with thousands of miles of use on many cars. Wayne Carini on “Chasing Classic Cars” also uses it. Why? It delivers what the advertising says. Using ATF or anything not specifically engineered for engine use is stupid, even if it works.

There are those of us who have had 200k + mile clean engines using no oil additives whatsoever.


Even 400,000 miles @circuitsmith. And using non synthetic oil with monthly 6,000+ mile oil changes.

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Exactly. It may be a GREAT product, but is it necessary?

I love the logic of people…

“Look - I’ve been using “produce-x” for decades and we’ve kept our vehicles running for over 200k miles.”

"Did you change the oil and filter on regularly in those vehicles for those 200k miles?


“So you’re saying it was Product-x that was keeping your vehicle running for 200k miles and not the oil changes?”


“Then why did you waste your money on oil changes?”


Mike, that’s a great argument!
A summary for 7+ years thread :slight_smile:

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