View Full Version : Additive needed to control moisture in diesel fuel?

03-26-2010, 01:49 PM
Have a Yanmar 4JH3-TE engine with about 350 hours. I keep both fuel tanks full all the time and generally find a very small amount (5 ml or less) of water in bottom of Racor fuel/water separator at end of the season. Given this, is there any need to use a fuel additive to remove small amounts of water from the fuel? I notice what appears to be rust (reddish brown) on the inside top of each fuel filter element both primary and secondary when I replace them after the course of one season. Probably use about 35 gallons of fuel/season. Presently use biocide, fuel stabilizer and cetane enhancer. Do I need one for water as well?

03-28-2010, 12:01 AM
If finding water in the separator, any amount, you might have a gallon or more in the tank!
Remove the fuel sender or suction tube, attach a copper tube to an oil-change pump, go all to the bottom of the tank and see what you get out.
Pump until clean fuel.
If possible try to list the boat to one side so you get the water at the lowest 'corner'.

04-01-2010, 04:00 PM
Thanks Haffiman 37 for the info.

Today, I removed the sending unit and rubber gasket from each of my two 17-gallon fuel tanks. I used a flashlight to inspect the contents. In the port tank, I saw a very small amount (spots) of reddish brown material on the bottom of the tank--sludge? I used my 5.5 gal. capacity manual oil pump and poly tube extension to suck up alot of this material. I also found the low side of each tank and made several removals of material from the bottom of each tank. Obtained 3-4 fl. oz. (90-120 ml) of water/reddish brown material from the port tank. Did not find any of this brownish material in the starboard tank and the water in it appeared to be about 1 fl. oz. or less. I added Water Absorber (West Marine) to each tank and stirred the contents of each tank til thoroughly mixed--this disperses the water. Recommended by Yanmar and Mack Boring to disperse water in diesel fuel. Looks like water in port tank may have come in around the sending unit gasket-- found some small cracks in rubber gasket. Replaced sending unit gaskets on both tanks. Will check the tanks again at the end of summer 2010.

04-01-2010, 06:58 PM
My mention of "5.5 gal. capacity manual oil pump"... in second line of second paragraph should be corrected to read "5.5 quart capacity manual oil pump"...