How important is Diesel Fuel Polishing?

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Moby Nick

Moby Nick

Senior Member
Joined
Jan 4, 2014
Messages
350
Location
USA
Vessel Name
Du NORD
Vessel Make
Albin-25
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.
 
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.
 
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.
 
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.
 
Mechanical diesels circulate several more times the amount of fuel they burn at WOT so fuel is being polished all the time.
 
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.
 
bayview said:
Mechanical diesels circulate several more times the amount of fuel they burn at WOT so fuel is being polished all the time.
Click to expand...

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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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 Biocide below. Change your filters at regular intervals and you should be fine.

http://www.marinedieseladditives.com/Marine-Diesel-Additives/Bio-Kleen
 
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.
 
bayview said:
You don't have to run at WOT the pump returns fuel at any speed.
Click to expand...

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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Ski in NC said:
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.
Click to expand...

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.
 
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.
 
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.
 
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).
 
psneeld said:
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.
Click to expand...

You are correct. Lehmans do not return much fuel. Not all diesels do.
 
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.
 
refugio said:
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.
Click to expand...

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.
 
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.
 
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.
 
All diesel fuel precipitates asphaltene over time, and ULSD has increased the amount. You don't need fuel polishing on a car because you burn it before it degrades. You don't need it on a 100 gallon boat tank because you also burn that pretty quickly. If you have multiple tanks, the return from the engine does you no good, nor does it do you much good in any case because the volume is usually pretty low - certainly well below the 2 - 3 gpm that would be considered a rate at which fuel can be efficiently polished. When someone says you don't need fuel polishing unless the tanks are cruddy it seems a bit like saying that you don't need wood preservative unless the wood is rotten. The whole point is to prevent the tanks from getting full of rubbish in the first place.

If you have multiple tanks, then you frequently need some means of transferring fuel. If so, the filters and a few valves are a relatively inexpensive add on that turns the transfer system into a dual polishing/transfer system. If you wait until a tank is nearly empty, then polish for a few hours while underway with the fuel sloshing around, then absent a load of bad fuel you will never have a dirty tank that needs dockside polishing, and never have a clogged secondary fuel filter. And if you do get a bad load of fuel, you can turn it into a good load with extra filters before it ever gets to your day/feeder tank.

The arguments against fuel polishing for vessels holding fuel for over 12 months, or those with multiple tanks, or those intending offshore cruising make zero sense to me. Below is a link to a description of the system I built for Delfin. I change the secondary filters pretty much for drill only as I have never seen the slightest build up of contaminants, even from the fuel that stayed in her for 4 years during her rebuild.

Fuel Polishing | Delfin
 
To truly "polish" your fuel onboard you need a strong enough pump to actually shoot the fuel into the tank to stir the (wait for it) spooge off the bottom of the tank where it is drawn off through a series of filters and returned to a clean tank. I'll bet that 99% of the onboard pumps are not strong enough to do this. Most systems that just transfer the fuel around are just wasting energy as contaminants sink to the bottom of the tank. If this simple transfer system were to be of benefit it would have to be left on for 24 hours a day, to prevent water from settling but nobody uses their boats that way. The best, simplest and most effective system is a recessed sump with a drain on it that may or may not be the fuel pickup that can be periodically drained, checked and if contaminated, discarded.
 
I am a firm believer in multi stage filtration over polishing. That has worked for me, so I'll contiue that practise.
With a single 120 Lehman and 360 gal capacity I routinely have to carry fuel more than 12 months.
 
Polishing has its place but not needed if tanks are kept clean and there is a good filtration system that is well maintained. If you look to polishing because the poop has already hit the fan than polishing alone is rarely the answer.
 
Xsbank said:
To truly "polish" your fuel onboard you need a strong enough pump to actually shoot the fuel into the tank to stir the (wait for it) spooge off the bottom of the tank where it is drawn off through a series of filters and returned to a clean tank. I'll bet that 99% of the onboard pumps are not strong enough to do this. Most systems that just transfer the fuel around are just wasting energy as contaminants sink to the bottom of the tank. If this simple transfer system were to be of benefit it would have to be left on for 24 hours a day, to prevent water from settling but nobody uses their boats that way. The best, simplest and most effective system is a recessed sump with a drain on it that may or may not be the fuel pickup that can be periodically drained, checked and if contaminated, discarded.
Click to expand...
Not really. You just need to do the polishing while underway with the fuel level low. This 'sloshes' the fuel around at least, if not more vigorously than you can with a pump.
 
eyschulman said:
Polishing has its place but not needed if tanks are kept clean and there is a good filtration system that is well maintained. If you look to polishing because the poop has already hit the fan than polishing alone is rarely the answer.
Click to expand...
The point of polishing is to prevent the tanks from getting filled with poop in the first place. It is what keeps the tanks clean. Filtration just removes the crud before it hits the engine but does nothing to clean the tank. If you go to any yard that has serviced a fuel tank you will hear them tell you that when polishing systems are used as designed, the tanks have no sediment build up even after years of use.
 
So far I'm with Delfin....long term storage of fuel can always use a little help in staying clean.

I doubt anyone who ever thought of polishing systems ever really thought they would clean the sludge out of a tank that has already formed....if you are polishing while underway in a storm...maybe you'll get the fuel clean before it clogs the main fiters...maybe not...I don't want to find out the answer to that one.

Getting grunge out of a tank I would call "cleaning"...keeping water, bugs, asphaltenes, rust, etc..etc...out I would call polishing.

Me...I carry a 100 gallons in nice new, poly tanks....burn it every week for 4 months, leave the tanks empty the other 8 while working....my kids can worry about a polishing system.
 
Bendit said:
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).
Click to expand...

Umm, I've only had to use my quick selector once, but that is enough.

Also, my FP system cost less than $1k to install and I now have a fuel transfer capability I didn't have before.

Reading this discussion, I think it comes down to how and where you use your boat.

If you never go out in bad weather or seas and you can always call sea tow, then you don't need it.

And to paraphrase Marin, the further you keep crap from you engine, the happier everyone will be.
 
Delfin said:
All diesel fuel precipitates asphaltene over time, and ULSD has increased the amount. You don't need fuel polishing on a car because you burn it before it degrades. You don't need it on a 100 gallon boat tank because you also burn that pretty quickly. If you have multiple tanks, the return from the engine does you no good, nor does it do you much good in any case because the volume is usually pretty low - certainly well below the 2 - 3 gpm that would be considered a rate at which fuel can be efficiently polished. When someone says you don't need fuel polishing unless the tanks are cruddy it seems a bit like saying that you don't need wood preservative unless the wood is rotten. The whole point is to prevent the tanks from getting full of rubbish in the first place.

If you have multiple tanks, then you frequently need some means of transferring fuel. If so, the filters and a few valves are a relatively inexpensive add on that turns the transfer system into a dual polishing/transfer system. If you wait until a tank is nearly empty, then polish for a few hours while underway with the fuel sloshing around, then absent a load of bad fuel you will never have a dirty tank that needs dockside polishing, and never have a clogged secondary fuel filter. And if you do get a bad load of fuel, you can turn it into a good load with extra filters before it ever gets to your day/feeder tank.

The arguments against fuel polishing for vessels holding fuel for over 12 months, or those with multiple tanks, or those intending offshore cruising make zero sense to me. Below is a link to a description of the system I built for Delfin. I change the secondary filters pretty much for drill only as I have never seen the slightest build up of contaminants, even from the fuel that stayed in her for 4 years during her rebuild.

Fuel Polishing | Delfin
Click to expand...

Really well said.
That's what I meant to say!
 
psneeld said:
So far I'm with Delfin....long term storage of fuel can always use a little help in staying clean.

I doubt anyone who ever thought of polishing systems ever really thought they would clean the sludge out of a tank that has already formed....if you are polishing while underway in a storm...maybe you'll get the fuel clean before it clogs the main fiters...maybe not...I don't want to find out the answer to that one.

Getting grunge out of a tank I would call "cleaning"...keeping water, bugs, asphaltenes, rust, etc..etc...out I would call polishing.

Me...I carry a 100 gallons in nice new, poly tanks....burn it every week for 4 months, leave the tanks empty the other 8 while working....my kids can worry about a polishing system.
Click to expand...
Getting sludge out that has already formed is beyond the scope of polishing and usually requires physically scrapping the stuff out. They call the precipitate asphaltene for a reason, so once it forms on the bottom of the tank it isn't coming out until you mechanically remove it.

We polish when we remember to do so. Turn the a/c motor on and cycle fuel while underway for 8 hours or so. The polishing filters are changed annually but could easily go 2 years. However, when a tank is low, I use that as an opportunity to get anything out that might have been missed before, so worrying about picking up crud and plugging the engine filters in a storm is not something I worry about. Since I buy fuel bulk every year or so being able to maintain it seems rational.
 
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