[Christ]

Anyone seen that "Guaranteed to pass" stuff? I've never played with it, b/c I don't need emissions inspection yet.

Other than that, I use SeaFoam (petroleum distillates) and Marvel Mystery Oil.

MMO is one that most people consider a joke, because it feels "gritty". That's because it is. It's machine oil with a crystalline polishing compound added. It's designed to polish metals in your engine, to help reduce friction.

When I get a new vehicle, I always change the oil, and use a quart of MMO. Over the next couple weeks, the MMO burns out, and I add oil every time it's low to keep the oil volume up.

I don't have empirical data showing what works and what doesn't, etc... all I have is "I saw it" evidence, which is good enough for me. I've been using it for years, and it doesn't cost that much, so it's not something I'm worried about, really. I also use it to clean gum/varnish and sludge build up, so even if it does nothing for the engine, it at least cleans it out!