It makes me wonder what viscosity you end up with.  Why put in a better oil with a cheaper oil?  Are you increasing the cheap or degrading the better?  Seems to waste quality either way.

If the motor runs good after using urine in the gas is that really good for it?  What is Mystery Oil reduces cylinder lube?  Why go to extra trouble instead of simply following original instructions? 

But if yo think it helps, it is your vehicle.

Makes me wonder how much longer you engine would run had you not done this.

I don't think you need to do this. The additive packages in the engine oil and gasoline should be sufficient for all driving conditions.

I think you are defeating the purpose of the synthetic oil by diluting it with dyno oil.

Marvel mystery Oil was originally designed to clean carburetors. Years ago the quality of gasoline was spotty and could gunk up a carburetor, thus Marvel Mystery Oil to remove the sludge, or at least try to. It's also good at freeing up stuck piston rings on engines that have sat for long periods, by simply squirting some in the cylinder and letting it sit.

I would say that putting some MMO in the tank once in a while and in the crankcase isn't a bad idea. I personally don't use any additives, but it does help maintain the cleanliness of your fuel system  and inside your engine. Sure, the oil and gasoline have additives already in them but hey. Its good to do a little extra due diligence even if you don't absolutely have to.   As far as mixing the conventional oil with synthetic... I would say that it isn't necessarily a "problem". I just don't see the point in doing it. You are better off just to use 100% conventional or 100% synthetic. Its kind of why almost nobody buys synthetic blend oil anymore. All the best

I think it's a waste of money

All good comments. I am thinking to go all Syn on my 2003 Corolla and all conventional on my 2001 Rav.  The comments on the obvious lack of thinking on mixing these oils is good.  I have no apparent reason to do so.  I just started doing it.  I am using the Amazon oils, which I find to be pretty good so far.  I use OEM Toyota filters, and I think I am just overthinking as I have never had any type of issue with the engines on these cars.  

As for Marvel, I think I will continue to do it in the gas and the oil (I do not add a lot).   I just wondered if it anyone knew of obvious problems.  I used it in my now junked Mitsubishi (and boy are those crap) and I am sure that it helped me from replacing the fuel filter.