Greetings! Over on the RV.net forum we have hashed this topic out to death on several occasions over the past year. While I think we're all pretty convinced of the merits of using synthetics in our RVs, one question always seems to be left unanswered. And this question would seem to me to be the main determining factor. Since synths can go longer in an engine without breaking down, what is the contaminent levels after a period of time? Say the synth is left in there for several thousand miles more than a dino, are there the same, more or less harmful contaminents? I realize that this may be a simplistic question, but I'm also hoping for a simplistic answer from someone. People have posted all kinds of charts, graphs & figures trying to show what's going on, but I'm hoping for the bottom line - and perhaps a link that shows in the simplest terms possible. Also, as a side bar, where does synth blends fit into the contaminent picture? BTW - The application for those of us on RV.net is mainly towing vehicles & motorhomes. Thanks!