While reading up on doing my first timing belt kit change for my 99 Impreza Outback Sport, (180K miles) I happened to read a post regarding Marvel Mystery Oil and adding it to oil change and gas tank.

 

So, I changed the oil yesterday and added the recommended amount of MMM and also added the recommended amount to the gas tank.

 

WOW! I had a VERY slight 'knocking' noise that I was starting to notice and it disappeared! Engine has always run good but now it seems a little quieter and is even seems to run a bit smoother.

 

I've tried different types of oil, synthetic and otherwise, and this is the first time I thought something deserved a post. Especially with a higher mileage car, this stuff sure can't hurt.

MMO is mostly a cleaner. Run it for 50 -100 miles or so and change the oil. MMO thins out the oil, and can clog the oil filter with dirt and particulate that it disolves and breaks loose from the crankcase. If enough crud gets in the filter oil will simply "go around" the filter media by way of the bypass valve in the filter. Then you get unfiltered oil running rampant through your engine.

 

Never heard of adding it to the gas tank. I use Seafoam for that.