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Old 06-16-2014, 08:35 AM   #1
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How important is Diesel Fuel Polishing?

The guy we bought our Albin-25 three years ago was big on fuel polishing; seemed every other sentence had the word "polishing" in it. He gave me a hand-drawn diagram showing which of a half-dozen valves should be "open" or "closed" for the process.

Well, I've never done it. My 1993 Dodge 250 never gets its fuel polished. The 1981 VW Rabbit Diesel I had before that never got its fuel polished.

We do not put many hours/year on our MD-17C, less than two tanks so far, though we'll probably surpass that this season.
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Old 06-16-2014, 08:42 AM   #2
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Clean fuel is important. Water in the fuel is bad. Cleaning can help prevent/remove water, which causes most of the fuel problems on a boat. However, just circulating the fuel thru a filter will not neccessarily remove the water, as it is not usually suspended. If you take the boat out and shake it up good, while cleaning, you can get the water out. Like your truck, boats that get used a lot and have small tanks have few fuel problems. Big tanks that sit a lot gather water.
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Old 06-16-2014, 09:12 AM   #3
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Well, considering the vast majority of boats don't have polishing systems on board and the vast majority of boats don't have any significant fuel problems, I'd say, while nice to have perhaps, they are not that important.
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Old 06-16-2014, 09:19 AM   #4
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I fitted a fuel polishing system a few years back with a view to long distance cruising. We carry up to 900 gallons on board. Since then I have used it intermittently to both polish fuel returning to the tank(s) and to provide additional filtration before the Racors. My conclusion so far is that it has not really been needed, though nice to have. Even fuel that is 3 years old at this point is still pink and fresh looking without much attention to polishing. I do use stabilizer additives for Winter storage and we do keep the vessel in the Northeast, so it is not as hot as down South during the year. I would guess that in a small vessel with small tanks, fuel turnover should be fast enough to not necessitate polishing. Just carry a couple of spare Racors.
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Old 06-16-2014, 10:59 AM   #5
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Mechanical diesels circulate several more times the amount of fuel they burn at WOT so fuel is being polished all the time.
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Old 06-16-2014, 11:52 AM   #6
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It's nice to have, but probably not critical as others have mentioned above.

Having said that, I usually polish new fuel, meaning, whatever tank I just put fuel in, I run the engine from the other tank until the new fuel as been polished for a few hours.

Most of the time, I see little difference in the vacuum gauge on the Racor.

BUT once or twice in the last year, my Racor got dirty immediately. So yes, my primary Racors would have caught it and, BUT why take the chance.
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Old 06-16-2014, 11:56 AM   #7
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Mechanical diesels circulate several more times the amount of fuel they burn at WOT so fuel is being polished all the time.
I think it depends on the engine and we don't run at WOT. Our FL SP135 returns about 1.8 GPH at 1800 rpms. Not what I would call enough to really polish fuel (we carry 700 gallons) but enough to get you in trouble if you don't return the fuel to same tank you're drawing from.
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Old 06-16-2014, 12:01 PM   #8
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You don't have to run at WOT the pump returns fuel at any speed.
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Old 06-16-2014, 12:24 PM   #9
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It was very important to me when I bought our boat and took it out the Golden gate and headed north the Columbia River. Put it this way, when you are out in seas and a filter plugs because of all the wave action stirs the stuff on the bottom of the tank, this is not the time to regret not having your fuel polished. It is also my understanding that if you hire a crew, there would be a requirement the fuel is polished. Now this is all about coastal cruising. It was the best $3K I ever spent!

If you are just sitting at the dock and the fuel has already been polished then all you need to do is periodic maintenance such as a Diesel Fuel Biocidebelow. Change your filters at regular intervals and you should be fine.

http://www.marinedieseladditives.com/Marine-Diesel-Additives/Bio-Kleen
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Old 06-16-2014, 12:47 PM   #10
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If your tanks are clean, you don't need it.

If your tanks have a lot of crud in the bottom, on board polishers will not remove it unless tank is agitated. And they only get agitated when in rough stuff with tanks at lower levels. So even with the system, you can get into trouble.

Dockside polishing only works if tank can be accessed between baffles. If poor access, gunk just sits there and the process is likely a waste of time.
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Old 06-16-2014, 01:15 PM   #11
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You don't have to run at WOT the pump returns fuel at any speed.
Not Lehman 120's up to a thousand rpm..... you are hard pressed to get any return. They run one in the training classes with nothing returning fuel in the parking lot.

Even at 1500 I determined mine to be so low...I just plumbed it back into the fuel supply manifold....maybe it's blocked and I'm wrong..but hearing the same from others...I don't think so.
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Old 06-16-2014, 01:25 PM   #12
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If your tanks are clean, you don't need it.

If your tanks have a lot of crud in the bottom, on board polishers will not remove it unless tank is agitated. And they only get agitated when in rough stuff with tanks at lower levels. So even with the system, you can get into trouble.

Dockside polishing only works if tank can be accessed between baffles. If poor access, gunk just sits there and the process is likely a waste of time.
Very true. Even then polishing the tanks won't get 100% of the gunk, but will get 98% of it. My tanks didn't have access, so the folks that did my polishing also installed some inspection plates for me.
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Old 06-16-2014, 01:31 PM   #13
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I was fortunate the boat yard I used had a portable pump and a couple of empty drums available. It would have cost a bundle to have them pump it out, and the fuel was of "indeterminate" age when I bought the boat. I pumped it completely dry and installed new filters (single tank, 150 gallons capacity). They used the fuel for the heater in the shop and it cost me nothing to get rid of, the best of possible situations. I think polishing is mostly applicable for warmer waters where the organisms grow faster and fuel capacities are large. If I start to see water in the Racors I plan to pump it dry again, admittedly hard to do if it's in the water.
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Old 06-16-2014, 05:34 PM   #14
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My boat builder discouraged me from spending money on a fuel polisher. I had an opposite view. My boatyard's project manager said it is a waste. Well, I've disconnected my polisher but have found its pump useful for priming the engine and transferring fuel among tanks. Still, if one uses sources of questionable fuel, a polisher should be in your plans.
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Old 06-16-2014, 06:42 PM   #15
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Polishing is "a nice to have" but still doesn't prevent a clogged filter in rough weather when the gunge at the bottom gets stirred up. We have dual primary filters with a quick selector lever for this situation - but haven't had to use it so far (10 yrs).
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Old 06-16-2014, 07:12 PM   #16
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Not Lehman 120's up to a thousand rpm..... you are hard pressed to get any return. They run one in the training classes with nothing returning fuel in the parking lot.

Even at 1500 I determined mine to be so low...I just plumbed it back into the fuel supply manifold....maybe it's blocked and I'm wrong..but hearing the same from others...I don't think so.
You are correct. Lehmans do not return much fuel. Not all diesels do.
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Old 06-17-2014, 12:40 AM   #17
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How important is Diesel Fuel Polishing?

So...polishing is not that important, but adequate filtration is critical, and backup filtration can be a comforting feature -that's the consensus, right?

How about transferring fuel between tanks? If you believe that is a worthwhile feature (independent of engine bypass doing it for you, and I can think of several scenarios where that could be a very valuable feature), then...if you run it thru filtration, you now have the pieces of a polishing system.

While I don't polish my fuel (beyond what I get from running the engine), I do have all of those pieces in place - and am quite happy to have them.
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Old 06-17-2014, 01:35 AM   #18
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So...polishing is not that important, but adequate filtration is critical, and backup filtration can be a comforting feature -that's the consensus, right?

How about transferring fuel between tanks? If you believe that is a worthwhile feature (independent of engine bypass doing it for you, and I can think of several scenarios where that could be a very valuable feature), then...if you run it thru filtration, you now have the pieces of a polishing system.

While I don't polish my fuel (beyond what I get from running the engine), I do have all of those pieces in place - and am quite happy to have them.
I built a fuel polishing system for my boat. It gets used. Here's how:
  1. Balancing the tanks. I usually use on tank on the trip out and the other on the trip back. Depending on current, etc, it doesn't always balance out.
  2. I find it much easier to fuel from one side of the boat, so I wait until I'm below 1/2 capacity and then empty one tank into the other. Then I only have to fill one tank. Or, if I'm just topping off, I use the polisher to top off the tank opposite the dock before buying fuel.
  3. Before fueling I push a bit of fuel back into the empty tank, just enough to keep the pump happy, and then circulate it. This keeps a fast flowing stream in the bottom of the tank. I do occasionally see a fleck or two of crud when I do this. Since the return is at the top of the tank, there's also a lot of splashing action, at least near the return.
  4. I will sometimes run the polisher for a minute or two before starting the engine. If there's anything loose (or moisture), I'll catch it in the polishing filter rather than the primary filter.
Number 3 probably isn't as good running the boat in 6' seas, but I'm sure it's slightly useful.
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Old 06-17-2014, 06:29 AM   #19
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I thought the same thing about adding a polisher on several of my boats and this one especially which has 1000 gallons on board I thought I would really need it.

So far not so, when I bought the boat it had been sitting for awhile in fresh water in KY with about 50% fuel in the tanks. I changed the filters added Racor gauges to the top of the primary filters and filled up the tanks with fresh fuel and headed off.

Now over a year later and just getting ready to turn off the Hudson into the Erie Canal and more than 70% through our Great Loop trip until we cross our wake we have never had any fuel issues to the engines.

We have been beat up a few times with bad forecasting including 9 hours in the gulf where we had to turn around in 8' seas and head back to port at 1am so I know that there has been a lot of tank sloshing going on.

I change my primary filters at the first sign of resistance and now I temporarily turn fuel off at the manifold just once in awhile to just check the gauges are working and they are.

When refueling I always ask when were the tanks last filled and how much fuel do they pump in a week, I won't buy fuel from just any place but go mainly to large facilities that fuel a lot of commercial boats and that also have good pricing. I stopped for fuel on the East Coast twice one was $3.54 gallon and the other was $3.69

So after about 4500 miles on this trip I am pleased that I used that polisher money elsewhere on the boat.
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Old 06-17-2014, 09:05 AM   #20
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Don't know how important fuel polishing is in terms of engine shutdown, but the liquid I remove from the fuel polisher every season has little relation to the undyed diesel with which I fill the tanks. Clearly I am removing something from the tanks with little cost.

Bay Pelican does not fill its tanks every year which may be a factor.
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