It seems like every time I turn around I find a new diesel additive on the auto store shelves. Many of them are promoted as fuel cleaners or econo-boosters, and a few claim to help prevent your in-tank fuel from transforming into a waxlike state in extremely cold conditions. While I haven't tried every diesel helper on the market, the dozen or so that have made their way through my tanks have greeted me with mixed results. On my older I.D.I (indirect injection) diesel I've often used additives to help lubricate the injector pump and have heard of many older-model diesel owners mixing in a quart of transmission fluid every few fill-ups to keep things running smoothly.
Recently I made yet another 3,000-mile trek cross-country with my '06 5.9L Cummins-powered Ram and tried a few "performance" additives along the way. With about 10,000 pounds in tow and averaging 14 mpg, I unfortunately can't say that I felt or observed any improvement in power or economy from the additives I mixed in.
By no means am I saying that all additives are snake oil, but I'm still not sure what long- or short-term benefits, if any, most additives will net.
Trying out a diesel fuel additive isn't really a waste (beyond what it costs) and generally won't harm your robust diesel engine. Be sure to follow the manufacturer's suggested fluid amount per tank, and do your best to simulate similar driving conditions while testing the additive. If you've found one additive that stands out above the rest, drop us a note on our forum at 4wheeloffroad.com and tell us how things added up for your diesel.