I used valvetech in the past, but have switched to BIOBOR EB for my boats gasoline engines. This product does it all, and is actually certified by the US Coast Guard. Costs less to treat same amount of fuel. They also produce BIOBOR JF for all diesel engines, and they produce a marine version called BIOBOR MD if you live in cold weather as it formulated to stop gelling and improves cetane for better cold starts. I use the JF in my diesel truck and have not had to change the fuel filter out in 50,000 miles. 16oz treats 1280 gallons of diesel and adds only a penny per gallon cost. Cheap insurance in my book!