I have always used it in my boat engines and yard equipment more or less as a gas conditioner because of sporadic use.
I have used it in my oil in the Jeep before oil changes mainly because of all the people who have had issues with sludge in the 4.7 V8 and I'll use it about once a year to clean the intake on both the truck and the Jeep.

I tend to like Lucas "Tune Up in a Bottle" for a regular fuel additive though...

 

I used it and just noticed that it smoothed out the idle. I didn't have that much smoke so I guess my plenum is holding up!

 

Hammer how would you say the Lucas fuel treatment stacks up against Marvel? I remember you talking about it once but am having a hard time finding the original thread.

 

I don't use Marvel on a regular basis. My old man and uncle were mechanics in the pit on weekends at a local stock car track when I was a kid and they both used the hell out of Lucas products. I've been using that gas treatment since I was a teen and never had an issue and never saw a need to change.

As far as the Marvel Mystery Oil, we use it when we get an ATV swamped and get water in the crank. I also have used it in my diffs way back when I had a Wrangler for play, when I've gotten water in there. It has an amazing property of getting water molecules to "stick" to it and really aids in getting all the water out of the crankcase or differential.
Never tried it as a gas treatment...

 

i will second the lucas products.......i use it every other fill up...................lol maybe i dont even need the sea foam