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Old 15-01-2009, 05:03   #1
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Diesel fuel quality tester

I sometimes have heard stories of people having engine problems and then needing some outside help. Quite often the reason is said to be bad fuel that they must have got at the last fill. Is there such a thing as a simple to use diesel fuel tester that one could use just at the time of putting the fuel hose into the tank. That way if there was a problem with the quality you would be able to see it before adding a bad batch to your tank. My tank holds 1600 liters and I would not like to ever get this problem.
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Old 15-01-2009, 07:23   #2
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not really. You can prefilter with a Baja filter as you fill your tank. Ideally learning how the fuel system works and repairs would be the best.
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Old 15-01-2009, 07:52   #3
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Fuel problems come mostly from moisture. The vent to the outside allows the expansion and contraction of the tank contents by use and by temperature changes to exchange the air above the level of the tank. It also can allow moisture to condense in the tank The water allows growth to form in the tank.

The water separator in the fuel system is designed to take care of that. You don't want water getting into the fuel system. It also can allow Algae to grow in the tank. That isn't so bad but they eventually die and settle in the tank. These accumulated dead bodies also are a problem and you fuel filter will handle that too.

You fuel filter system does a pretty good job of deal with all this in normal conditions and you don't have to worry most of the time. What can happen is conditions can make it possible to accumulate a lot of water. It happens when the fuel level is low and the boat is on the hard during the winter. It's very common when you buy a boat that has been for sale on the hard to have a fuel tank full of crap.

A full tank minimizes the amount of air in the tank and reduces the amount of moisture you might condense. This is a good thing to do when you lay up the boat for a period. Tank treatments work to a point. If you have a lot of crap in the tank adding an algae treatment only kills the ones that are alive. It's the dead ones that make the problem. Many fuel facilities have the fuel treated already. I know it is where I get my fuel. Over treatment of tanks is a bad thing to do. If you decide to follow a treatment program do it no more than directed and you probably need to do it with each fill. Once you have the problem it's too late.

You can find a lot of snake oil and magic devices out there. Some claim to work better than others. Many claims are overstated. I've never seen any serious proof any of them actually help.

Changing your fuel filters often will alert you to rising problems. Take the filter apart after you change it and look inside. See what you see. If you see some stuff well you know the filter works.

If you have inspection ports, open them up and look. If you have no inspection ports consider adding them. They make port kits you can install without removing the tank.

Before you think about installing a fuel polishing system I would step back and do the math. A good dual Racor 500 system will provide good filtration and the ability to swap filters on the fly. Adding complexity has it's potential problems too. You might clog a filter some day. If you were out there swapping it would be very simple.
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Old 15-01-2009, 10:19   #4
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Good diesel has no water nor large particles. That's pretty much it. Your fuel delivery system must have water traps and filters to take care of that.

Even if there were such a thing as fuel tester, you still need water traps and filters.
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Old 15-01-2009, 11:06   #5
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I'm going to disagree a lot with what Paul just said.

First, I don't believe that water gets in through the tank ventilation system if that system is installed and maintained properly. I believe that most water comes in with the fuel or through a leaky fill cap gasket. In fact I would bet that most water comes in through improperly maintained fill caps.

Using a Baja to filter 1600 liters will be a pain as they are very slow. One way to test before filling the tank is to fill a clear glass jar with fuel and let it settle for a few minutes. You should be able to spot water or dirt and make a decision whether to fill up or not.

I feel that a good quality fuel polishing system is well worth the price if you can afford it. You could make a very good one from parts. Just ensure that both the pickup and return to the tank reach to within an inch or so of the bottom of the tank and are at opposite ends of the tank and separate from the engine fuel supply lines. You need to match pump, lines and filter in order for the polishing system to work properly. A good fuel polishing system will keep your fuel and tank in good order by removing water, bugs and ashphaltines that settle out of the fuel. They work best if the tank is clean at installation.

Steve D'Antonio has written much about fuel polishing systems and their value. You may be able to find out more from back issues of PassageMaker magazine.

My personal experience with a clogged fuel line in a seaway has colored my views I'm sure.

Good luck.
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Old 15-01-2009, 11:24   #6
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I think I'll have to agree with much of what Paul says....also the fuel in the tank is warm do to the temperature of the fuel being returned from the engine.
When the engine is stopped and the fuel cools it creates low pressure drawing in the outside air and all its moisture.
BTW this is similar to how you get moisture in your engine oil when there is nothing wrong with it!
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Old 15-01-2009, 11:29   #7
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Its both, water coming from moisture in air and leaks from fuel caps etc. How much of each really depends on the boat, how the skipper operates the boat and where the boat is located such as in climates with high humidity.
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Old 15-01-2009, 12:17   #8
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David Pascoe did some thinking and math on water getting into the fuel through condensation. He concluded that air entering the tank was not problem and added very little if any (my paraphrase) water to the tank. I was wondering if anyone here has done the math or would be willing to do the math on this hypothesis? I certainly don't have the ability to do that but Mr. Pascoe's article certainly rang true to me. However I would like to see well thought out and justified information that could prove him wrong. Mr. Pascoe also mentioned water in engine oil. Interesting read.

The Myth of Condensation in Fuel Tanks by David Pascoe: Boat Maintenance, Repairs and Troubleshooting
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Old 15-01-2009, 13:09   #9
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To answer John's question directly, there is really only one test a recreational boater can do--visual inspection. Luckily, this test catches 99% of the problems. Fuel oil must be clear and bright. Clear means the absence of particulate matter and bright means the absence of water. Water will show up as a haze if it is in sufficient concentration to be a problem. You can still have water dissolved in fuel that passes the "clear and bright" test, but that level of contamination is rarely a problem, unless you are storing the fuel for a long period. If you want to get really anal, you can buy water indicating paste and reject any fuel in which the paste changes color. Water seps and filters are generally good enough, unless the fuel is heavily contaminated. Then you get microbes which clog your filters.

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Old 15-01-2009, 20:30   #10
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Having had the experience of going into diesel fuel tanks I can tell you that there is no myth to water condensing inside a fuel tank. The main differentiation is the relative size of the tank and the relative amount of water.
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Old 15-01-2009, 20:54   #11
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I have never been able to figure out why diesel tanks aren't built with a sump and drain. One could simply drain a bit of fuel (or water if it had accumulated) and check for water and other crud.
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Old 16-01-2009, 01:16   #12
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Extactly

Quote:
Originally Posted by stevensc View Post
I have never been able to figure out why diesel tanks aren't built with a sump and drain. One could simply drain a bit of fuel (or water if it had accumulated) and check for water and other crud.
Steve
Having owned and operated a commercial fishing boat, that is exactly what we had. I guess most Commercial boats are built with maintenance being a higher prority. Every spring after the boat had sat idle for the winter A small petcock in the bottom of the tank was opened and the water and crude drained and examined.
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Old 16-01-2009, 05:10   #13
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Quote:
Originally Posted by stevensc View Post
I have never been able to figure out why diesel tanks aren't built with a sump and drain. One could simply drain a bit of fuel (or water if it had accumulated) and check for water and other crud.
Steve
because the insurance industry and ABYC have decided that a valve in the bottom of the tank is a bad idea.
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Old 16-01-2009, 07:37   #14
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Never Monday is correct ABYC and USCG prohibit fittings on the bottom on recreational tanks I have a 1/2npt bung on the top of the tank over the deepest point. I can drop a rigid plastic tube to the bottom and pump a pint or so off the bottom every so often using a simple outboard fuel bulb. I do this when the fuel is setteled. Every once in a while you get a little crud and water. Better to know then to find out later.
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Old 16-01-2009, 08:22   #15
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Quote:
I have never been able to figure out why diesel tanks aren't built with a sump and drain.
Never Monday has it correct. Something under a tank can't be serviced unless you add a trap door under the boat. I wouldn't want ti on my water tank either. Connections are where tanks leak from. if you had a nice engine room with accessible tanks you could have large access ports so you could not only drain it but clean out the sludge and all that. For a recreational boater it is not always possible to remove a tank from the boat easily. I can remove the tank without destruction of any part of the boat. It's more the exception than the rule. Some tanks are so buried they have to be abonadoned. Some of the old Allieds have a thick solid teak floor (no plywood)with cast iron tanks buired so deep it's a serious amount of destruction to get a peak at them.

Having large access ports on top is the next best thing. It is a good idea to be able to get in there and look around and deal with cleaning the tank at some point. After 20 years you can almost be sure it needs it.
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