Hi Charles. I asked my Yanmar dealer about this specifically when getting the annual spares this year (Poole area), as I had heard horror stories of the dangers of not using red diesel. He was very reassuring, and said that road diesel was in fact much better for the engine as it contained lots of healthy additives and preservatives, and was much cleaner. I find I only use a tankful or so a year as the Yanmar 1GM10 is so frugal, so cost is a minor consideration. Tim