Originally Posted By: Cujet
As many of us know, anything you add to gasoline will, to some extent, end up in the oil. Products that partially or entirely evaporate are not much problem, for obvious reasons. However, if over an Oil Change Interval, one adds a few quarts of MMO to the gas, a more than negligible portion of that will end up in the oil. How much depends on the engine, the ring sealing, the quantity added and the OCI length. I'm not sure partially burned and contaminated MMO does wonders for the oil.
I will admit, my 2003 Jaguar X-Type runs significantly smoother "if" I add MMO to the gas. I was having trouble with a rough idle, added some MMO and absolutely noticed the difference in MPG and smoothness. However, it did not fix my rough idle, which was due, at least in part, to a vacuum leak.
What you're saying is correct. Though with or without an additive the some of the percentage of the unburnt fuel will find its way into the oil too, maybe even a bit more w/o a UCL. The UCL might provide a better ring seal, as reported by some who claim their engine is running smoother and quieter with the additive in the gas. Fuel by itself has no lubricating properties at all. Fuel with a UCL will have a bit more lubricating properties, especially TCW3 which a fair amount of people are using. MMO is a lubricant as well, not as good as TCW3 though. If the fuel does flash off 100% and the small amount of UCL remains behind in the oil then the oil level could very well rise during the OCI.