[quote author=2310160A1710620 link=1214081739/15#19 date=1214175192]
KwakNut wrote on 06/21/08 at 17:34:18:KwakNut, what has your education in the oil industry told you about upper cylinder lubricants such as Marvel Mystery Oil or Redex? MMV has been used for 60 years or so as an oil mixed in the gas tank or directly drawn into the intake manifold via a valved tank. It is not supposed to burn in the combustion chamber, and is supposed to lubricate valves, their stems, and the entire upper cylinder area on its way in and out of the combustion chamber. It is supposed to help protect these areas by reducing the cylinder temperatures, especially if it is drawn into the cylinders from an outside holding tank. It is supposed to soften carbon deposits on piston tops and valve surfaces, or prevent the formation by keeping those parts wet with itself. It is my understanding that this oil distinguishes itself only in that it will not burn in the combustion chamber and thus not foul anything, and that its primary use is that it lubricates areas that don't see engine oil.
On the whole, some of those sorts of products are pretty good. Valves benefit from lubrication, and any surface that can collect carbon and muck benefits from the detergent properties.
What you have to remember though is that fuels, just like oils, come with addictive packs – and they vary hugely.
Buy cheap fuel from an ‘unbranded’ supplier, and there aren’t likely to be lots of additives in it. Buy from one of the majors, and you’ll get their additives, which help with keeping things clean (like injectors and the back of valves) and lubricate as well (valves, injector pumps etc).
Lots of the majors share fuel distribution depots, and when the different tankers from different companies turn up, they add their own additive pack to the tanker as it's being filled – in effect, the good ones are putting their own version of Redex in at the pump.
If you want to recover a gummed up old motor, Redex-type products are great because you can add them in greater concentration. If you want a healthy engine to last, you can either feed it on good quality fuel, or feed it cheap fuel and try to compensate with additives - which probably costs more in the long run than buying the better fuel!
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