Diesel Polishing

[Knock-on]

I need to build a Polishing system on a 29ft Yacht.

What necessitated this was a bit of an infestation of the dreaded Bug so I have spent hours going over the basics and now have a rough idea of what I want to accomplish which is probably a million miles away from what I need to accomplish.

So, the scenario I currently have is a clean tank with a nice new inspection hole cut in the top. The tank is approx 70l.

My goal is to have a permanent, cost effective Polishing system that can be activated every 3 months to recirculate 5x the capacity of the tank to polish the fuel and turned off.

I plan on attaching a pickup that lies on the bottom of the tank that will pass through the inspection lid leading to an inline disposable fuel filter which in turn leads to a comprehensive filter / water separator, pump and finally return to the inspection lid with a pipe located about mid depth inside the Tank.

My main stumbling point concerns the main filter. I can put in an in-line disposable 30 micron filter for a couple of quid and it will last until it visibly looks ready to change. This will stop any serious contaminates clogging the secondary filter but what secondary filter to use?

You can get a standard CAV 296 housing and filter with a glass water separation bowl for £20 but finding the Micron value for these filters is not straight forward. It seems to be anything from 2-20 Micron and little definitive rating for individual filters.

Then I am unsure what Micron rating will be optimum to achieve a clean fuel for my particular operation. You can spend £???? on a system that polishes it to the nth degree but what is realistic given that most people don't bother from year to year to do any maintenance on their fuel and get along fine. Will a 296 type give me enough performance or should I install a Racor 120 and what benefit will it offer over the CAV?

If there is a tangible benefit in spending more money I do it but not just for the sake of it and not until I understand the rational behind it.

Finally, will polishing every 3 months stop the microbes forming or would an inhibitor with modern diesels still be a prudent measure?

Thanks in advance for your comments

[a64pilot]

Polishing will not stop “bugs” only a biocide will stop bugs, polishing if done correctly just cleans the fuel, if not done correctly it pretty much doesn’t do much at all. If you have bugs and kill them with a biocide, polishing will remove the dead bugs or much of it anyway, often bugs cling to the tank wall and it takes a physical force to clean them off.
I don’t polish my fuel, I don’t see the need, I don’t believe there is any real tangible benefit.
It can’t hurt though, just more money to spend on what I consider to be a non necessary item.

Now if your fuel source is dodgy and often you don’t get clean fuel, then by all means do everything you can to ensure you get clean fuel, including polishing, but I have never gotten dirty fuel, and my filters apparently last hundreds of hours and for years, so what’s to polish?

Arguably the engine polishes the fuel, my 4JHE returns far more fuel than it consumes, so by the time my tanks are low the fuel has had several passes thought the filters, so the last of the fuel is cleaner in theory than the first.
But a fist sized fuel filter will filter hundred if not even thousands of gallons before it need changing, so the fuel must not be very dirty to start with.

Again, if I were changing filters with any real frequency at all, then I’d look into polishing.

As far as additional filtering, in my opinion we would be better off with a high bypass oil filter, but that’s not popular so you never hear of it.
A lot of things are considered must haves because people on the internet tell you that you must have them, but the overwhelming majority of boats do not, and apparently don’t need whatever the item is.

[Bill O]

Is this a new to you boat and you have a cruddy tank?

I agree w/A64 you probably don't need a continuous polishing system in place unless you are getting your fuel from questionable sources. Once you add a biocide, you will kill the algae and create a large amount of crud in you tank. This will fall to the bottom and sit there (possibly w/a layer of water also) until you hit some rough weather then it will all get stirred up usually then clogging your primary if you are running your motor.

I've opened up some tanks and they don't have any crud on the walls, while a couple of others did have it on the walls. It does take a few hours of work to put a correctly sealed cleaning port.

I've make my own fuel filter/polisher from a Racor 500 (10 micron filter) and a small automotive fuel pump. I had >200 gal. of fuel that had been sitting for years and I had no idea what condition it was in when I purchased the boat. I used metal tubing to pick up off the bottom of the tank (where the water/crud accumulates) after adding the biocide and pulled all the fuel out through the fuel hose neck on the tank. I then pumped it bank into the tanks to use on out 1100 nm return trip. On that trip the "old" fuel ran fine and we never clogged/changed a filter (we motored/motor sailed the whole way due to time constraints).

It's been a while since that initial tank cleaning/been in some rough conditions while motor sailing and we don't even see a blip on our fuel vacuum gauges. Some will argue that its not like the high volume polisher the commercial cleaners use but seemed to work for me.

[s/v Jedi]

So, assuming a currently clean tank, this is how we did it:

(We have sumps in the bottom of the tanks, with drains, so that is where we connected the system. If you use a suction pipe with top fitting like for drawing fuel to the engine, you need to attach a small piece of fuel hose to that, which is just long enough to lay flat on the tank bottom).

You only need one filter/separator. I used a Racor 500. I recommend the expensive marine version which has that metal bowl underneath the glass... not just because it’s required but because it has a better option for drain valve. I replaced that with a 1/4” small brass valve with hose barb to make draining crud easier and cleaner. I use a 30 micron filter element until throughput is reduced enough to annoy me, then throw that out, clean housing and put new element in.

Next choice is a good pump. It must be compatible with the max. flow rate of the filter. I use a Walbro 500 iirc but Walbro has different models now.

From tank to filter to pump to fuel return line. Always keep the filter on the pump suction side.

Like a64 wrote, this is not enough to prevent infestation. In theory, keeping moisture out should keep them away, but I recommend to use enzymes as well (Startron diesel formula).

To take care of a current infestation, use maximum dose of Biobor + maximum dose of Startron. This has been tested as the most effective way to deal with it. Give it time and filter many times.

[s/v Jedi]

I forgot to add: with the 30 micron polishing system, you can use 2 micron pre filter elements and only replace the engine mounted filter when it gets old or rusty

[s/v Jedi]

Sorry for flooding this thread. Here is the diagram for an extensive system. Google s/v Jedi fuel system for full description

[Pete7]

We built our own which is a tad simpler to Nicks, from a Cav filter and Facet fuel pump. However, despite using it regularly it didn't resolve the problem which had built up over twenty years. The diesel bug had the consistency of custard and needed a paint scraper to remove. We still use it occasionally since the take off is right at the bottom of the tank so removes water. We haven't had a re-occurrence since but do use a bug killer at each fill up.

I guess the best you will achieve with a fuel filter in addition to the filtering the engine as A64 points out, is to remove the water from the fuel. Btw, have you changed the o ring on your fuel filter recently, often a source of the problem.

Anyway, our design:

Pete

[noelex 77]

There are really two types of fuel polishing systems. A boat installed system that operates frequently and a professional system that is used only occasionally (often when a problem is detected).

The aim of boat installed fuel polishing system is to remove any water and sludge as soon as is forms. By continually removing these elements, diesel bug has little medium to flourish. In addition the polishing system seems to remove the need to do the horrible job of physically cleaning out the diesel tank (or at least extend the interval). As it can be operated when sailing or in rolly anchorages, the boat’s motion provides the mechanism to stir up the tank. Usually these systems operate frequently and therefore filter very high volumes of fuel.

Our system is usually on most days for at least a few hours. So we filter about 200L (50 gallons) a day, perhaps 40,000L (10,000 gallons) a year. This volume of continously filtered fuel cannot be compared to the much smaller volume filtered by the diesel return mechanism. As well, when we refill the tank we use an external filtering funnel so the volume is filtered multiple times by the polishing system before the fuel ever reaches the engine.

Professional polishing sytems are slightly different. These use high volume pumps and filters with adjustable nozzels to blast any debris off tank walls and the bottom. The aim is to clean the tank rather than to operate on a continual basis to prevent the tank becoming dirty in the first place.

Both boat installed and professional polishing systems seem to work well and for cruising boats, especially those in more remote locations, these are worth considering. Fuel problems are becoming very common.

The system proposed in the first post post by Knock-on (if I understand it correctly) is similar to a boat installed system. Operating such a system only every few months I don’t think will be frequent enough to achieve the aim of removing water and sludge as soon as it forms. Without the large pump and high volume filters used by the professional systems, it will not be all that effective at a cleaning a tank that is already dirty. On the other hand, it will not do any harm and may well do enough good to at least be a help.

[Bill O]

Originally Posted by Pete7

We built our own which is a tad simpler to Nicks from a Cav filter and Facet fuel pump. However, despite using it regularly it didn't resolve the problem which had built up over twenty years. The diesel bug had the consistency of custard and needed a paint scraper to remove. We still use it occasionally since the take off is right at the bottom of the tank so removes water. We haven't had a re-occurrence since but do use a bug killer at each fill up.

I guess the best you will achieve with a fuel filter in addition to the filtering the engine as A64 points out, is to remove the water from the fuel. Btw, have you changed the o ring on your fuel filter recently, often a source of the problem.

Anyway, our design:

Pete

Our portable looks very similar to Pete's, but w/the racor 500 instead.

The system that Nick illustrated is also similar our "designed" polisher system except it has a centrifugal drop out "filter" as a polisher. So far (knock on wood), we have not needed to install the in-line polisher since we take the time to keep the water out by per-filtering our fuel before it goes into the tank. The in-line polisher is on my list, but not the priority list.

IMO the in-line polisher system is something useful for high volume fuel tank capacities (>200 gal.) or if one gets fuel from questionable sources.
For the OP with possibly a 30 gal. capacity, it maybe a bit overkill to put in an in-line system vs. good pre-filtering practices and periodic full tank filtering to keep things in check.

[Knock-on]

Thanks for the feedback.

I have a clean tank now and plan to keep it that way

I need to put a system in place as might be in a situation where need to separate sea water from contaminated fuel without available assistance.

Main question is what value has something like a Racor have over a CAV?

[a64pilot]

In my opinion for a polisher to work correctly, it needs to be done like Jedi describes.
First you need to be pumping a LOT of fuel, then you need the suction hose and return hose to be positioned in such a manner to get a stirring current going in the tank, and that takes high volume.
If you don’t do this then your only “polishing” a small area around the suction hose.
Of course you can do it under way and hope that stirs things up enough.

But if your not clogging filters, what’s the point? And if you are clogging filters, find out why, don’t just band aid the problem.

So far as fuel return rate, the only spec I know of is for the Dodge PU truck with of course the Cummins engine, it’s used to determine if there are injector problems, bad injectors return too much fuel, but for it, it’s 180 ml in 30 sec with the engine fully warmed up and at 1200 RPM.
That is a whole lot of fuel.
Fuel is used primarily as a cooling agent for Diesel engines, my Duramax even had a fuel cooler just as the return fuel was dumped back onto the tank, lots of fuel flow keeps the HP pump cool and the injectors too, compressing fuel to high pressures significantly increases its temp.

At the end of a day motoring, feel your fuel tank, I bet it’s warm.

[Bill O]

Originally Posted by Knock-on

Thanks for the feedback.

I have a clean tank now and plan to keep it that way

I need to put a system in place as might be in a situation where need to separate sea water from contaminated fuel without available assistance.

Main question is what value has something like a Racor have over a CAV?

IMO the racor is a little better since it does 2 types of particle/water reduction in one. The "turbine" creates the centrifugal action and drops out heavy particles and water which collects in the bowl. The second, is the water repellent filter. With the CAV you can't do a visual inspection of the filter since it enclosed in metal.
Maybe it just personal preference but many have complained about air leaks in the CAV filters.
If you are not in a hurry, look around for a used Racor 500 and it will be much cheaper than new, even if you need to rebuild it.

[RaymondR]

On my old boat I had a Rube Goldberg gizmo that I built out of a spaghetti storage jar with a 12V gear pump to circulate the fuel and a Finsbury oil change pump in parallel with the gear pump to prime it. The filter element was a fabric bag made from two layers of heavy denim.

I found that if I circulated the fuel around a few times that even with a bad infestation the bag filter was sufficient to clean the fuel to a degree where I did not need to change the engine filters. I concluded from this that the DIY filter was doing a sufficiently good job of filtering out the particles of gunk so as to not require any further filtering.

[Pete7]

Originally Posted by Knock-on

Thanks for the feedback.

I have a clean tank now and plan to keep it that way

I need to put a system in place as might be in a situation where need to separate sea water from contaminated fuel without available assistance.

Main question is what value has something like a Racor have over a CAV?

Both will work, but the Cav filter is available the world over on a Sunday morning. Couple of ££ from the local auto factor this side of the pond.

Pete

[noelex 77]

Originally Posted by a64pilot

So far as fuel return rate, the only spec I know of is for the Dodge PU truck with of course the Cummins engine, it’s used to determine if there are injector problems, bad injectors return too much fuel, but for it, it’s 180 ml in 30 sec with the engine fully warmed up and at 1200 RPM.
That is a whole lot of fuel.

Deisel engines vary significantly in how much fuel they return, but that is less than 0.4 litres a minute. Given the low engine hours of a typical sailboat this is a very small amount of filtered fuel compared to an installed fuel polishing system. The fuel polishing system also has the advantage that it picks up the fuel from the very bottom of the tank where the water and sludge accumulate.

The reason installed fuel polishing systems work is that they filter the total fuel volume on a regular basis, eliminating the environment where diesel bug can grow. A small amount of extra fuel filtered while the engine is running may help, but it is not the same. Our main engine has not been run for 10 days, but we have filtered an estimated 2000 litres of fuel from the very bottom of the tank with the polishing system during this period of time.

Polishing systems are not expensive, but are arguably overkill if you have access to good quality clean fuel, but it is a fallacy to think that the small volume of filtered fuel returned to the tank by the engine is the same thing.

However, don’t neglect the other good fuel practices. Fuel polishing is only one part of good fuel management. Try and buy clean fuel from high volume retailers. Test a sample of the fuel before accepting it. Use a filter before it enters your tank. Make sure your fuel intakes cannot ingress rain or seawater (the typical flush deck fuel fill relying on “O” ring to stop water entering the tank is silly, in my view). Use a biocide. Have large access hatches for cleaning in your tank, and consider installing a day tank system if this is practical.

As a final step, a small amount of diesel in a jerry can with a system to enable the engine to draw the fuel directly from this separate source can get you out of trouble if your man tank is clogged up with fuel bug. This only requires a few parts such as some fuel hose, but could be difficult to rapidly jury rig in an emergency if you have not considered the problem beforehand.

Fuel problems are unfortunately very common on long distance sailing boats.