The forum population generally takes a dim view of "snake oils" (especially the ones with PFTE) that are purported to do everything from clean your engine to allowing you to drive cross-country with an empty crankcase.  Yeah, right...

However, one product has gotten our attention - Marvel Mystery Oil.

Typical forum question:

When I am mowing when its hot and I am running engine hard for a while, motor starts to cut out and lose power like a valve just quits sealing. No backfiring, just compression loss, or so it sounds. Let the tractor rest 10 or 15 minutes, starter up and go right on running fine again. Also, it doesn't do this every time I mow. Any Ideas?

Typical forum answer:

I would bet that you have an exhaust valve sticking. My tractor had problems with getting hot and quitting, these guys suggested putting Marvel Mystery Oil in fuel to help lubricate valves and this stuff works. I tried it for a while. No more problems, also, I changed the head gasket the other day, just to inspect, and inside of my motor looked like it had just been cleaned, no carbon anywhere! This motor also would not start well when hot, and sometimes backfired a little, doesn't do that anymore either.

Other thoughts from the forum:

• 3 pints of oil in most of our K's. That's 48 ounces. Given the MMO formula, 1/5 of your normal oil capacity should be MMO - 48 / 5 = 8.4 ounces.
• I throw about 1-2oz of MMO in the gas tank whenever I remember, about the same amount in the crankcase when I change the oil, too. And the exhaust smells, well, interesting...
• Directions are on the can, I don't know how it works, but when you take the head off a motor after using it for an extended period of time (3 or 4 months), the engine looks like new inside, no carbon. I have ran it for a long time and since have had no more exhaust valve problems with my Kohlers. O.K., bottle says add 4 oz. to each 10 gallons of gas or diesel. Says right on the can, eliminates valve sticking. Hope this helps!
• One more comment about MMO. It works great as a fuel stabilizer during the winter months. I use it my SEADOOS, SNOWMOBILE and CUBS. The stuff never gums up and it's a lot cheaper than Sta-Bil. 
• After discussing a while back about the miracle oil for sticking valves, I talked to an airplane mechanic friend of mine. He agreed and proceeded to tell me that they used it in their planes. He said at teardown time, the engines were much cleaner inside. I picked up a can at advance auto, not sure how many ounces, but a square can, looked to be about a quart. I mixed this in 5 gallons of gas. It doesn't smoke at this mix, and performance has increased noticeably. I'm not a lubrication engineer so don't go pouring this in your Lexus until you get more professional info. but it works for me, and clean is good!!!!!

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