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kitthackeray 23-04-2017 07:03

cleaning diesel tanks that have been unused for some time.

My woosen schooner was built in Malaysia about 30 years ago, and there are three tanks each with four hatches. Theyre made from mild steel and painted outside with epoxy. Problem is, you cant get to more than half the hatches, and the internal baffles mean each tank is divided into 6.

Visual inspection shows clear diesel about 3 inches deep on the bottom, and there is some sludge, not much, at the edges and corners. This is a brown ferrous sludge, small particles only. The plates themselves and the tank sides ring true and have a light oxide coating.

So, no way to inspect all the interiors, but how to clean out whats in there??

I read a post some time ago about pumping diesel out, through a filter, and back into the tank thus filtering it till it was clear. Perhaps with the addition of a chemical??

I would be most grateful if someone can shed light on this, obviously its happened before a score of times.

Let me thank any respondent in advance - were in southern Portugal.


Kit Thackeray

Fiveslide 23-04-2017 07:28

Re: cleaning diesel tanks that have been unused for some time.
It's called fuel polishing. It really won't do much, if anything, for the sludge you're seeing unless you can break it loose somehow with the fuel being pumped back in.

Can you get us any pictures of the insides of the tanks? What needs to be removed to get to the rest of the inspection hatches and make room for a proper tank scrubbing?

kitthackeray 23-04-2017 10:40

Re: cleaning diesel tanks that have been unused for some time.
Dear Fiveslide,

Have to dismantle half the boat..... no, weve gone as far as we can with hatches. 3 tanks, 400, 500 and 700 litres. The boat is at Isaura do Mar – Sailing Cruises.

Nothing much to see in the tanks. Slight rusting on the dry surfaces. I thought to tip fifty litres in each tank and go out in a few waves for an hour. Maybe this would put the solids in suspension so they could be filtered.

Im not even sure what kind of a pump or filter you need for this kind of work, it takes power to push through a filter, but how many microns?

Grateful for your reply



sailah 23-04-2017 17:50

Re: cleaning diesel tanks that have been unused for some time.
Im copying this from another post I made so I don't have to type it again.

This is the fuel polisher I have on my boat. It works awesome. Uses inexpensive filter elements that are industry standard so probably available anywhere. My tanks are spotless after running this for 2 years.

You could adapt the design and get a 220v motor/pump but having it onboard is nice to keep it clean. There are companies that come to your boat with a polisher setup similar to this mounted on a cart and polish on the docks.

I borrowed heavily from this webpage: Strider Fuel System

The main components are (2) Shelco stainless steel filter bodies (FOSBN-786), a 12v Carter fuel pump (P4070)

The rest is just fittings, fuel line, hose clamps, a DPDT rocker switch, a 12v relay etc.

This is the schematic I used:

I custom made 2 parts which aren't really available, 1 is a bracket to hold the filters and the other is an aluminum tank bung.

Here's what it looks like installed. The aluminum bracket holds the Shelco filter housings. I bought these because they are US made, very high quality SS housings, I paid $16 each on eBay, that accept industry standard filter cartridges. I buy filters from McMaster Carr for about $5/each in any micron you could want. I use 10 micron filters and a pair easily filtered 100 hours x 72 GPH or 7200 gals of fuel with no apparent reduction in filtering capacity.

In words this is how it works:

I made a new tank bung that that I use for a fuel pickup. You can't use the engine pickup because it will starve the engine for fuel as I found out. I made the bung from aluminum. The in tank portion I tapped for a pipe thread. I used a NPT compression fitting to attach some flexible 3/8" soft copper. I test fit the dip tube until I had found the very bottom forward part of the tank. Once it was bent perfectly and the right length (lots of trial and cutting with pipe cutter) I secured it by tapping the tank for some small SS allen cap screws and black RTV sealant.

I drilled a hole in the tank using a hole saw. At first I was worried about the small amount of chips in the tank but let me tell you, the polisher works well!! Hoovered up the chips and they were all found in the first filter housing.

So the fuel pickup leads into engine compartment and into the first filter housing (1). The fuel line then exits the first filter (2) and goes to a Carter P4070 fuel pump (3). This a 72 GPH pump. It works really well. At anchor the noise would be annoying but I only run when the engine is running so it's a non issue. After it leaves the pump, it now pushes fuel through the second filter (4). From this point I would typically return the fuel to the tank. I have a sight glass I found in my parts bin to check fuel (5).

The other bit of functionality I built into the system is the polisher can act as a backup to the main engine lift pump. By opening (6), closing (7) you've now shut off the racor and are supplying 10 micron fuel to the engine. I tried this out underway and it works great. Can change out the stock Racor element, under power, and prime the Racor back up with fresh clean fuel and then put the Racor back online and go back to polishing fuel.

To power the setup, I run it off a DPDT rocker switch mounted on the port external side of the engine compartment (quarterberth area). In the down position it runs the pump off the 12V system, so it's ON any time the main battery switch is on. In the UP position, it runs when the engine is running, I tapped power from the Balmar smart regulator, fed this to a fused 12v relay. This is how I run it 99% of the time. So when the engine is running I'm polishing the contents of the tank 2x an hour. For spring commissioning I run it for a few hours and make sure I've gotten all the junk at the bottom of the tank.

If I were to do it again I think only one filter is necessary. These filter elements are pretty large. I ran the same pair all season long with maybe 100 hours of engine time. When I took them apart the first filter housing had all the aluminum chips and black sludge. The second filter was spotless. I would normally change a Racor mid season but when I checked it it looked new too. I assume this is because the polisher runs through far more fuel in an hour and caught all the junk before the Racor had a chance too. The turbine bowl also was free of almost any sediment compared to the year before. I ran the 2 filters because I bought 2 on ebay for $16.00/ea and I like overdoing things. If you were to run a single filter you'd want the filter before the pump to protect it, thus "pulling" fuel through.

dbaublis 24-04-2017 09:23

Re: cleaning diesel tanks that have been unused for some time.
2 Attachment(s)
After a clogged filter during a turbulent sail (the boat was new to me and had not, apparently, been sailed hard in heavy weather in a while) I re-plumbed my fuel filtering-pumping system to provide ability to both prime the Racor filter and use the Racor as a kidney. It also puts the fuel pump after the Racor, which is the preferred configuration as the Racor operates best in suction. Here is my piping flow diagram with normal operation flow path shown by the green line. The pump is represented by the circle with a triangle in it.

For kidney operation (Red Line), I replace the operating filter (usually 30 microns as the engine fuel filter is 10 microns) with a 2 or 10 micron filter and let the systems run while at the dock or in heavy weather sailing. I am putting a switch in to allow pumping operation with the ignition off. Set the valves as indicated. When done, remember to change filter back to operating filter, empty the bowl as necessary and reset the valve lineup. You may or many not need to prime the system again.

To prime (Blue line), set the valves as indicated and just crack the cover of the racor to allow the air to escape. As soon as the bowl in the racor fills, keep an eye on the level as you don't want to geyser diesel out of the top of the Racor. When almost or completely filled, stop pump and re-valve to normal operation. The rest of the system can now be bled as normal. New diesels do not need to be bled.

Stirring the tank can be done with hard sailing or anything that will agitate the diesel. It is not as effective as high pressure cleaning of the tank but will get most out as well as filter any new fuel which may be dirty or contaminated. The entire system just required some valves, fittings and new hose, which was a good idea in any event. Next design will have more optimization done on the fittings and valving.

DeepFrz 24-04-2017 09:50

Re: cleaning diesel tanks that have been unused for some time.
sailah, You have it right, IMO. Something you might do, as you have two filters already installed, is put a 2 micron element in the second filter. Well done.

sailah 24-04-2017 12:47

Re: cleaning diesel tanks that have been unused for some time.

Originally Posted by DeepFrz (Post 2378335)
sailah, You have it right, IMO. Something you might do, as you have two filters already installed, is put a 2 micron element in the second filter. Well done.

Thanks! I would be remiss in not giving full credit to SV Strider and her skipper who was my inspiration into modifying the system to meet my needs.

In my second filter housing (the one the pump pushes through back to tank) I have a 5 micron filter. Maybe I forgot that from the write up. First filter is 10 micron, second is 5. My engine filter is 2 micron.

McMaster does have 2 micron available though , but they're 11 bucks instead of $4.86 :biggrin:

I think the other thing that works very well was the careful fitment of the dip tube to be a the very bottom corner of the tank. Any sediment that collects in this area gets immediately sucked up by the polisher and not the engine dip tube. I usually run the polisher for a minute before I start the diesel for this reason.

Originally I used their diagram and shared the common dip tube already in the tank. I found out the hard way, barely making it thru Hull Gut on sail with my 7 y/o daughter, all her friends and moms, that the polisher pump wins the battle with the engine pump:banghead:

Once I added a dedicated polisher dip tube, it's been flawless.

Maka 24-04-2017 13:51

Re: cleaning diesel tanks that have been unused for some time.
The question remains: How does one break loose the gunk in the bottom of the tank?

DeepFrz 24-04-2017 13:58

Re: cleaning diesel tanks that have been unused for some time.
You get everything set up so you can reach in and scrub it out. Or you get things so you can get a pressure washer in to wash it out. Sometimes there is no easy way. I got caught off the NW corner of Cuba with a clogged fuel line. I wouldn't want that to happen to anyone.

Bleemus 24-04-2017 16:18

Re: cleaning diesel tanks that have been unused for some time.
A professional with a high capacity fuel polisher can do it just fine. An additive to help loosen the sludge is added and they must alternate the position of the return line to get all the sludge into suspension. Baffled tanks without multiple access ports are a real challenge. Contact FuelTec Systems in North Carolina and ask them if they have any pros with their gear in your area. Its the best.

Ken Z 24-04-2017 16:32

Re: cleaning diesel tanks that have been unused for some time.
dont know of avialability of resources if you can pump out and remove your tanks and take them to a radiator shop and have them clean them out . I did that this spring with my pearson, a aluminium tank, when partially cleaned out i found the pitting to be bad, I replaced the tank. good luck.but they did a good job on other tanks, dont do it with poly, but you have steel.

Lepke 24-04-2017 23:43

Re: cleaning diesel tanks that have been unused for some time.
The issue of dirty tanks/fuel comes up every month or so. It's not that complicated. If you have a primary filter like Racor that has a element and a design that separates out water and a secondary of almost any kind, you have a basic fuel polishing system. I have dealt with long sitting diesel/dirty tanks at least a hundred times maybe hundreds of times. Unless someone shoveled in dirt or sand in volume, your filter system will filter it out. Using a good fuel conditioner will break down the sludge with a few fillings along with the motion of the ocean. The sludge dissolves (with a good conditioner) into tiny particles your filter catches. The conditioner helps extract any water so your filter housing separates it out. Carry extra filters, but you probably won't need them.
For example, my current boat has 1942 steel tanks that had no inspection openings. The fuel had sat for 6 years. At the time I used Algae-x conditioner at about 3x the normal mix. With it I added new fuel so the old fuel was about 60% Some tanks were empty so I added new fuel and 3x conditioner. I did a sea trial, no problems, Changed the filters and came home (500 miles, North Pacific in winter), no problems. 2 years later, I put in inspection ports during a remodel. I went inside to inspect. The tanks were clean, no sludge, light surface rust. Some pits in the bottom that I welded. I now run a 2 micron (in the primary) I change it at about 500 hours by vacuum gauge reading. My mains alone pump 70+ gallons an hour thru the primaries. So in 500 hours about 35,000 gallons (plus what ever the generators and boiler used) have been thru the filter.
I use a conditioner every time I fuel at the normal mix rate. I have clean (2 micron) fuel and I make sure I buy clean fuel. Currently I use Archoil AR6200 and it is excellent. It also helps the burn so much I get about 10% better mileage. My diesel 4x4, 3/4T PU gets 25mpg at 65mph. and I use about 8.5 gallons an hour @ 10kts in an 83' 80 ton boat w/DDs. I usually buy it on Amazon or Ebay. I don't make any money on it.

kitthackeray 25-04-2017 01:15

Re: cleaning diesel tanks that have been unused for some time.
I would like to thank all those who replied to my query. Sailah really went to town and the guy with the ex uscg boat has obviously seen a dirty tank or three. Thanks to all, I have my answer and will get the job done.


Kit Thackeray currently in Portugal

Squanderbucks 25-04-2017 04:24

Re: cleaning diesel tanks that have been unused for some time.
Regardless of your ability to remove the sludge at the bottom you will forever be plagued with dealing with the very fine rust clogging your fuel filters. The surface oxidation caused by storing the tanks nearly empty for an extended period of time exposed the steel surface to oxygen and no matter how you get the sludge out this will likely always be a problem.
Theoretically if you could get out any scale, and sludge the tanks could be filled with Ospho mixture and allowed to pickle for several days the drained and flushed might be helpful.
To continue using these tanks you should clean as best as you can possibly installing additional cleanout ports and install two or three filters in series such as Racor 30, 10 and 2 micron sizes each with filter monitoring gauges. And once cleaned keep the tanks full as much as possible.
Squanderbucks was built with 100 gallon steel tanks and I removed them back in the 90's and replaced them with custom fiberglass ones.
Very fine rust is very hard on the injectors of a diesel or carburetors of gas engines.
I had a gas engine boat that had gas purchased in an out island place where the fuel was carried down to the boat by rolling 55 gallon steel drums to the boat - what a nightmare - the boat was forever dealing with the bronze micron filters on the carb being clogged at the most inopportune times.

Snowpetrel 25-04-2017 05:17

Re: cleaning diesel tanks that have been unused for some time.
Maybe consider a day tank of some sort. Only put filtered fuel in it from the potentially contaminated tanks.

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