Never used them as additives on a regular basis, but I used Seafoam to help get a Honda CB-650sc running after it sat in my garage for about 5 years. Just poured it into the carbs and let it soak overnight, then kept turning it over until clear. Finally was able to get it moving to the shop for a full carb cleaning. I'm also very skeptical about using any magical additive as a rule, but I think there are some solvents that might help with cleaning once in a while.

 

I wouldn't use any of those products unless you are trying to fix a particular problem that has occurred. Seafoam might help to remove a very high level of carbon deposits inside an engine, but if one has been using a Top Tier certified gas (with has a minimum detergent package), or occasionally using a fuel injector cleaner in your gas like Techron, it is probably not necessary to use anything else.

 

I run marvel mystery oil in my fuel tank and in crankcase every oil change on my wife’s sienna and my gmc envoy with the 5.3. I can say oil is cleaner when changing even going the same miles as before and fuel mileage is slightly better each tank. Is it worth jumping up for joy no but its very cheap piece of mind. Its like 3 bucks for a big bottle of it from walmart. It lasts me about one oil change and 5 tanks of gas or so. So i buy 3 bottles at a time and last me a good while. I never believed that stuff either but mmo works in my stuff. Also used it when i had my corolla too and it worked great. The part i love is its so cheap.


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I run marvel mystery oil in my fuel tank and in crankcase every oil change on my wife’s sienna and my gmc envoy with the 5.3. I can say oil is cleaner when changing even going the same miles as before and fuel mileage is slightly better each tank. Is it worth jumping up for joy no but its very cheap piece of mind. Its like 3 bucks for a big bottle of it from walmart. It lasts me about one oil change and 5 tanks of gas or so. So i buy 3 bottles at a time and last me a good while. I never believed that stuff either but mmo works in my stuff. Also used it when i had my corolla too and it worked great. The part i love is its so cheap.

If adding Mystery Oil (I don't know what is in it) is so great, why don't auto manufacturer's recommended it, and why don't motor oil companies, and gas companies, add it to their products?

Toyota says that one should not add anything to your gas tank or your motor oil, except for occasional fuel injection cleaner in the gas (especially if not using Top Tier Gas).

 

Pass on Moly, waste of money.YES for Seafom and Transtune.
Absolutely recommend. Used on ALL cars since 2003, never a problem, always great results. Use both via oil and gas tank. I use Seafoam on older vehicles via oil before oil changes, run it there for about a week.