I have never been a fan of additives. We put thousands of hours on our previous boat with 6-354T Perkins and they always ran great and never sooted the transom. We bought our new boat with 3408 435 HP turbo CAT's. When we bought her she had 3900 hrs . on them and a NL 8kw genset with 9200 hrs. Yes, 9200! The guy we bought it from was the original owner and said he had never used any additive. I sent oil samples from both engines to the CAT lab and they said that the oil samples compared to those of the same engine with 1500-1800 hrs. They surmised that the PO ran them easy as I knew I would do. When I asked about life expectancy, they said that I shouldn't care about hours much anymore but should track fuel through the engine. The harder you run them the more fuel they will burn but there will also be more wear at higher speeds. They said they commonly see in excess of 50,000 gallons frequently on my engine and also have seen many of the 3408 NA's reach 100K gallons and more. I have burned slightly over 5000 gallons since we bought her in March of 2013. Never any additives. Never any soot. Nothing goes through there if it hasn't been polished. I did run out of fuel once when the boat was new to us. That was due to valve position confusion on my part. I had plenty of fuel, just not in that tank. If the PO ran the same way I do and keeping in mind the result of the oil samples, then I will optimistically assume that I will get 60 to 70K gal so lets say 65000 gallons before those CAT's are worn out. At, say 7.5 kts., then I should be lucky to live long enough to see those engines turn over 9000Hrs. Man I hope so. That would qualify me as a seasoned cruiser. But, this topic was about fuel additives. Yes, all engines vary but I currently have two CAT's and two Northern Lights that seem like they will never quit. Previously, I had two Perkins and one Westerbeke that never failed me in 15 years of ownership. So here is my final two cents worth---(I could have made this post a lot shorter with just this one sentence.) "Stop spending money on additives and instead spend that money on keeping clean oil and clean fuel in your engines." Over and Out Greg Heart of Gold Currently lying Biloxi MS www.seaplanetearth.com Cell 765-603-0201