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Old 06-17-2014, 09:53 AM   #21
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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
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Old 06-17-2014, 11:28 AM   #22
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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.
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Old 06-17-2014, 12:01 PM   #23
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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.
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Old 06-17-2014, 12:32 PM   #24
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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.
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Old 06-17-2014, 01:09 PM   #25
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Originally Posted by Xsbank View Post
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.
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.
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Old 06-17-2014, 01:13 PM   #26
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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.
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.
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Old 06-17-2014, 01:33 PM   #27
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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.
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Old 06-17-2014, 01:37 PM   #28
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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).
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.
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Old 06-17-2014, 01:40 PM   #29
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Originally Posted by Delfin View Post
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
Really well said.
That's what I meant to say!
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Old 06-17-2014, 01:41 PM   #30
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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.
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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Old 06-17-2014, 01:48 PM   #31
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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.
I estimate that my sp135 returns about the same amount of fuel that it uses. So, I use it to transfer fuel to trim the boat a lot. Also bc the port fuel feed valve is hard to reach!

By the way, I'm no engineer, but it seems to me that the return's main function is to cool the fuel charge and keep it cooler than it would be otherwise. So if your just returning it to the fuel manifold, you're defeating its purpose.
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Old 06-17-2014, 01:59 PM   #32
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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.
Since "polishing" (what a stupid term IMO) does nothing to stir up the fuel in the tank, how exactly does it keep the fuel "polished"?

Unless the crud that may be in the fuel is in suspension the extra filtration is just filtering clean fuel over and over. Even if the system draws from the lowest point on a tank it won't do much unless the tank is low on fuel and is being stirred up in a rough seaway since fuel tanks are baffled.

I think your money is far better spent on dual change on the fly filters with large surface area elements then on a "polishing" system.
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Old 06-17-2014, 02:07 PM   #33
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I estimate that my sp135 returns about the same amount of fuel that it uses. So, I use it to transfer fuel to trim the boat a lot. Also bc the port fuel feed valve is hard to reach!

By the way, I'm no engineer, but it seems to me that the return's main function is to cool the fuel charge and keep it cooler than it would be otherwise. So if your just returning it to the fuel manifold, you're defeating its purpose.
That may be truein a 1:1 mix...hot fuel mixing with fresh...

But before I did the return to the manifold trick...I did a lot of research.

Still not trusting everything I see and read..I decided to test my engine (and genset to be sure) setup.

I disconnected and placed the return in a jar. After 15 minutes I has less than a oz in the jar so I increased the RPMs...at 1500 RPM and 10 minutes later I had maybe a quarter ounce more....

So I figured the total heat gain after travelling though all the piping, brass return manifold and the big brass fuel manifold, plus a racor and fuel pump plus on engine fuel filter...and being mixed with well over 10X the amount of fresh fuel...just maybe it doesn't make a difference....and it didn't over the last 2500 mile trip.

Others here have posted that their return line was plumbed back into the supply line from the factory is what got me thinking in the first place.
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Old 06-17-2014, 03:07 PM   #34
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Since "polishing" (what a stupid term IMO) does nothing to stir up the fuel in the tank, how exactly does it keep the fuel "polished"?

Unless the crud that may be in the fuel is in suspension the extra filtration is just filtering clean fuel over and over. Even if the system draws from the lowest point on a tank it won't do much unless the tank is low on fuel and is being stirred up in a rough seaway since fuel tanks are baffled.

I think your money is far better spent on dual change on the fly filters with large surface area elements then on a "polishing" system.
I think you may have missed the oft repeated injunction that fuel polishing is done while underway. The lower the level of fuel, the more agitated the fuel is, even with baffles. Plenty of sloshing around and plenty of contaminant removal, which is why cruisers using polishing systems never seem to need to have their tanks cleaned out. They stay clean.
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Old 06-17-2014, 03:50 PM   #35
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When I had a sailboat, small diesel tank, but less usage too, I had frequent plug ups of my Racor. Especially in the predictable conditions of lots of sloshing around, and of course in conditions where use of the engine was absolutely necessary.
But... that stage of my life ended when I bought Retreat, in 1994. Since then, I have noticed a marked improvement in the clean-ness of the fuel that I purchase, I now have two rather large tanks, 300US Gal each, and I try to leave them full over the winters, so the avg age of the fuel in the tanks is now over two years. Yet, I now go through Racor filter elements about every 4 years, (I keep track of this in my maint. log) and have never had a plug up. The return of my Volvos is likely more than the consumption, but nowhere close to the volumes suggested above as being necessary to a polishing system. I think there is a lot to be attributed to the modern refining and filtering that goes on before I get my fuel. It seems like it gets polished, so all I have to do is keep it from degrading and no furhter polishing is necessary.
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Old 06-17-2014, 04:18 PM   #36
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When I had a sailboat, small diesel tank, but less usage too, I had frequent plug ups of my Racor. Especially in the predictable conditions of lots of sloshing around, and of course in conditions where use of the engine was absolutely necessary.
But... that stage of my life ended when I bought Retreat, in 1994. Since then, I have noticed a marked improvement in the clean-ness of the fuel that I purchase, I now have two rather large tanks, 300US Gal each, and I try to leave them full over the winters, so the avg age of the fuel in the tanks is now over two years. Yet, I now go through Racor filter elements about every 4 years, (I keep track of this in my maint. log) and have never had a plug up. The return of my Volvos is likely more than the consumption, but nowhere close to the volumes suggested above as being necessary to a polishing system. I think there is a lot to be attributed to the modern refining and filtering that goes on before I get my fuel. It seems like it gets polished, so all I have to do is keep it from degrading and no furhter polishing is necessary.
Refinery standards filter the fuel to 30 microns. 2 to 5 microns can damage common rail systems, so on that basis the freshest fuel is already contaminated. The asphaltene precipitates out after that final filtration and collects in the bottom of the tank absent polishing and those particles are big. All polishing is designed to do is keep the fuel at refinery specs over the period time you use it. We polish at 30 microns and transfer fuel at 10 microns to reduce the load on the secondarys. You can run just fine for years on the filters placed on the engine, but the reason you read about people having their engines stopped when they get frisky in a seaway is because that precipitate gets stirred up and overloads the system.
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