Tech Wiki

Water in Your Fuel?

How to determine if you have water in your fuel

By Capt. Al, Kindred Spirit


A primary filter should have a see-through bowl with a drain so that WATER can be rapidly detected and removed. A sample should be taken from the filter at regular intervals. A visual inspection with a flashlight may show the water in the bottom of the bowl. Water will be clear and the fuel will have a color. Drain if necessary. I do it with the engine running to allow any air bubbles to work through the engine without stalling.

Regular fuel filter changes must be at the top of any maintenance schedule.

What happens if you don't check for water... And how to get rid of it

By Tom P, IMPULSE #233, (1986)

I recently lost my engine (Univeral 25hp) due to dirty fuel. I found that the filters were not very dirty, but found that the electric fuel pump (transfer pump) wire filter was jammed slam up.

The current configuration is that the fuel leaves the tank, goes through the electric fuel pump, then through a Racor particulate/water separator, then to the engine (engine has another filter as well). The solution to this is to have the Racor filter in line BEFORE the electric fuel pump.

Flushing the fuel tank

This is the method I'm currently using to flush the system; out from the tank, through the Racor filter, THEN through the transfer pump, then through 20 feet of temporary fuel line to the fuel tank fill neck.

  • The first thing I did was attempt to draw out the bottom (water?) of the fuel tank...I did this by inserting a hose through the fill neck and used an oil hand pump...The only problem is that it was hard to determine if I was actually on the bottom of the tank. Therefore, I drew out a gallon or two, then adjusted the hose and took another gallon or two, then adjusted the hose a third time and took another gallon or two. End result was I removed about 6 gallons; and although I didn't let it settle very long (about 10 minutes), none of it appeared to have any water in it.
  • The next step was to add the proper amount of BioGuard Fuel Microbiocide Additive in order to kill the growth (minimum 3 hours to work); I went with this brand because it was the only one I saw that claimed it could successfully treat an already contaminated system.
  • Then I purchased three each Racor filters, Model R24T which filters 10 microns (R24S is good to 2 microns). I cleaned the transfer pump screen, installed the 10 micron racor, and disconnected the fuel line going to the engine, and attached 20 feet of hose to reach the fuel fill neck (used fuel hose as to not risk another type of rubber breaking down and causing more problems).
  • I let the transfer pump run for about 30 minutes, at which time the pump seemed to slow down. Turned the pump off and checked the Racor; found a little bit of dirt and the fuel looked very cloudy in the bowl. Then checked the transfer pump screen; found a lot of dirt...Cleaned the screen and decided to change the plumbing so the fuel goes through the Racor first, then through the transfer pump...I also blew back through the tank line to clear the pickup tube screen...
  • I let the pump run for one hour, at which time I thought it was slowing down again...Found the Racor was considerably dirty; the bottom bowl was very cloudy and the filter had a lot of particulates visiable. I changed to a new filter. The transfer pump screen was not dirty at all. Blew through the tank pickup line again to clear it's screen.
  • Next I swapped the plumbing around again; this time so it would draw from the 20 foot hose through the fuel neck, then go through the racor, then through the transfer pump, and into the tank via the normal pickup tube (reverse flow).
  • I let this setup run for 1 hour, adjusting the 20 foot hose every once in awhile to try and get some stuff off the bottom...The pump didn't like this method very well since I couldn't successfully get all the air out of the system (pump was noisy), but it was moving fluid. So an hour later, I checked the filters once again. The racor had slight contamination and the transfer pump was still clean.
  • Next, I changed the plumbing back so it was drawing off the regular tank pickup, going through the racor, through the transfer pump, then through the 20 feet of hose to the fill. Let this setup run for an hour. The fuel in the racor bowl looked very clean the entire run; the first time it didn't cloud up. The filter element had some minor particulates. The transfer pump screen was clean.

I had to stop at this point for the day. The next day I called Valvtect Inc, the makers of the BioGuard additive. The bottle says use only 1 oz for 30 gal of fuel (est. I have 15 gal in tank, so .5 ozs was used) to kill existing growth. My question to them was if a little will do a little good, will a lot do a lot of good; and without causing any engine/fuel system damage. Their nice technician said that I could add more without risking damage, but the "kill rate" would not increase. He told me that if it makes me feel better, adding another ounce, or two, or three will not hurt the engine but will probably not kill more growth either. He went on to say that given my description above, I've most likely successfully cleaned the system. He also advised using another additive as well; Diesel Guard Heavy Duty Marine Diesel Additive (West Marine)...Said it would help break up any water deposites, help stabilize the fuel duing non-use, as well as improve diesel performance. The tech said it is fine to use both additives at the same time. Therefore, I plan on getting this other additive as well.

So my next move is to add a little more of the BioGuard, add the Diesel Guard, and circulate the fuel another hour. Then give the engine a try; go sailing, hopefully bounce the tank around a little and see what happens.

I also talked to the techs at Racor. They also suggested that if I still have a contamination problem to (1) install a larger filter; larger in size, not larger in microns. The the larger filter would hold more trash before shutting down the engine. Or (2) install a "kidney loop"; a separate fuel loop with filter and pump to constantly circulate the fuel within the tank while the engine runs, or put a separate switch to circulate/filter the fuel while in rough seas...I'm not going to this extreme, just wanted to convey their thoughts. Their tech was also confident that my actions thus far have solved the problem.

All the above wasn't very hard to do, or very expensive. I opted not to pull the tank because Valvtech and Racor both said it could be handled in the above manner.