Marvel Mystery Oil (MMO) is somewhat heavier than gasoline, and gradually sinks to the bottom of the tank where it is picked up and consumed. So the concentration in your tank decreases over time or distance.
- MMO: 25.6 g/fl ounce (I weighed a quart on a scale with 2g resolution + did the math to allow for the weight of the bottle)
- Gas: 21.26 g/fl ounce (from wikipedia), see the "Density" section.
I've had nearly equal success whether adding 2 oz or 4 oz per 10 gallons gas. 2 oz/10 gal isn't quite as good as 4 so I suspect 3 oz/10 gal might be fine.
This all started when I found tthe availability of lean burn decreases after about 250 miles or 5 gallons (at ~50 mpg). I suspected the MMO is sinking to the bottom and being sucked up by the pump faster than the gasoline. The recirculating fuel system helps keep it mixed but there's nothing like splashing in a fillup to mix it all up.
At the 5 gal mark I'll be adding some MMO to keep the concentration up. Not sure exactly the dose and whether I'll add fuel at the same time or not.