How much water in the fuel filters is Ok? - Page 2 - SailNet Community
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post #11 of 14 Old 10-07-2013
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Re: How much water in the fuel filters is Ok?

Oh my Jesus! No no no!! Why are you saying this? Have i gone mad? What data? What data?!

This is from BP, a fuel manufacture.

This is from John Deere, engine manufacturer:

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I will even include a link to a letter from some guy who works for a legitimate company, not because he is knowledgable but because some people like official letters.

A storage tank manufacture:

Diesel | Information On Petrodiesel & Diesel Fuel
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post #12 of 14 Old 10-07-2013
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Re: How much water in the fuel filters is Ok?

If you are using the same fuel in your car, check the filters in it. It could be that you are getting wet fuel. Are you getting it from a high volume diesel supplier? Some stations don't turn there stock over very quickly and can get a lot of water in there tanks. So stick to truck stops and stations you see a lot of movement at the stinky pump. Marine diesels will drink pretty bad fuel without much complaint as they are relatively robust, but cars are not. For instance VW high pressure pumps can be destroyed by very little moisture and will set you back many thousands of dollars. This is the reason the only way I would buy a VW TDI is if it was new or owned by someone I know and the last new car I bought was in 1990 so I don't like new cars.
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post #13 of 14 Old 10-15-2013
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Re: How much water in the fuel filters is Ok?

Conventional wisdom seems to go with keeping your fuel tanks topped off. That has always been my practice and it is not often that I ever get more than about two ml of water out of the glass bowl in about every 10 hours of running.
I have only ever had a bad dose of water in the fuel once in more than 30 years of running diesels in boats. This occurred last year when filling from a dockside pump which had a long, black hose running from the shore-side bowser out about 50 metres to the deep end of the jetty. The hose probably held at least five gallons on its own, and being black, I imagine that it got hot and humid inside. So when I filled, that first five gallons of old diesel in the hose between the pump and the nozzle probably had half a gallon of condensation mixed with it.
Although the glass bowl on the low pressure filter was nearly full of water before I caught it, no water found its way to the high pressure filter on the engine. However, after clearing the water from the tank I did change both the low pressure and high pressure filters just to be safe.
So....some water in the low pressure filter is probably unavoidable and nothing to worry about provided that you have a program to drain it off at regular intervals.
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post #14 of 14 Old 10-15-2013
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Re: How much water in the fuel filters is Ok?

Originally Posted by RichH View Post
Think about this .... do empty tanks magically fill with water from condensation? of course not....
I hate to argue with Rick, but in this case he is provably wrong. I have tested this specifically on different scales, from lab to thousands of gallons.

No, an empty tank would not fill with water. When dew falls from the roof it lands on the bottom and evaporate on the next nice day. What happens, however, is that the water falls through the oil and becomes trapped where it cannot evaporate. The process is slow and will not amount to more than an ounce per year, depending on tank size, climate, and the position of the tank in the boat. But an ounce can lead to a lot of corrosion and bio-growth issues.

CAT apparently has seen the same thing (from the link below)
"Water Contamination
Water can get into your fuel if itís mishandled by your fuel supplier. Most often, however, water gets into fuel tanks by condensation from the atmosphere. As the tank empties, air enters the tank. Water condenses on the walls and runs down the sides. The water never evaporates because it's heavier than fuel and goes to the bottom of the tank.
After this process is repeated several times you may have a significant amount of water in the bottom of your tank."


No valve; maintaining a clear vent is critical to safety.


The greatest risk is almost certainly your own fuel filler cap. In fact, any time there is more than a few ml of water, there has been a leak into the tank, either on the boat or in the distribution chain. But given that fact that, in general, boaters have water problems and truckers do not, suspect condensation.

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With a 20 gallon tank operated 100 hours/year, old fuel is not a big problem; I would fill the tank. I would tend to agree with Rick if the fuel was going to be kept more than 6 months. Condensation or not, fuel tends to darken and deteriorate over time.

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