Diesel Tank

[Liam]

We've had problems with crud in our diesel tank since we've bought the boat. I replaced the fuel filter about a month ago, and noticed that the old filter was full of what looks like black cotton wool. Anyway coming back from our week away, on Friday, I set off and after cruising for about 10 minutes the engine started racing and then slowing down, until it eventually stopped.

 

I took the filter off and noticed that after only being on the boat for about 4 weeks, it was once again filled with this stuff, which I beleive is diesel bug. I replaced the filter yet again with the spare we always carry and after bleeding, the engine still wouldn't start. The problem was that some of this stuff had made it's way to the manual fuel lift pump and blocked it. The fuel pump was replaced and after bleeding, it caused no problems for the 3 hour cruise back to the moorings.

 

We're wanting to drain the diesel tank thoroughly, as I think there's some water in there aswell which this diesel bug is living off, but the problem is that the diesel tank is completely sealed with only the fillter, breather and dipstick holes. We could use a pump to get rid of the old diesel through the filler hole but I'm wanting to do a "proper" job and make sure it's completely clean.

 

The integral steel tank is in the central engine room and is fairly accessible, and we're thinking of making some sort of inspection/cleaning hatch in but how to go about this is the question or if anyone has had to clean their tank out in the past without an inspection hatch what's the best way of doing this?

 

Thanks in advance.

[smileypete]

Hi,

 

I'd just try siphoning out any water and try a water removing additive to start with.

 

These make any residual water dissolve into the diesel instead of separating on the bottom of the tank.

 

'Fuel Set' is a well known one, there are loads more.

 

A coarse filter before the lift pump would help catch any large debris.

 

cheers,

Pete.

[DaveR]

I used a small hand / bilge pump with a suction thin tube stuck to a cane.

 

Last time I did this I took nearly three litres of crud from the bottom of the tank, since then no problems.

[Liam]

I know it's a while ago now since I posted this but thanks for the advice. We started pumping out the tank this weekend with one of those drill pumps.

 

I had no idea that the tank was that big. Before we started it was only about half full but w've filled 4 20L Jerry cans and 2 and a half 25L drums. There is only around half an inch left in the bottom now, and we're going to tackle that next weekend.

 

It was pretty akward to do really. We started off with the pipe down the filler hole but natually, pipes always curl, so although we got the majority of it out that way we needed to change our tactics. We couldn't fix a pole to the pipe as the filler pipe has a kink in it. In the end, we had to use the very small hole in the top of the tank which is covered by a small cap. We use this for dipping the tank and it's only about 1/4 inch wide. There was no room for the pipe aswell as a stick or even straightened coat hanger so what we ended up doing was putting the straightened out coat hanger inside the pipe, with the end of the pipe about 6mm from the end of the coathanger, and then into the tank that way.

 

To keep the pipe from touching the bottom of the tank I simply bent the coathanger in a few places and it seemed to stay still!

 

We're also looking into getting a hole cut in the top of the tank for inspection purposes which obviously can be covered. What I'm wondering is, how would you go about cutting into 6mm steel when the tank is in the central engine room inside the boat? Is there a need to be cautious regarding the sparks from say, a cutter mixing with the diesel in the tank? I suppose we could always pour some water into the tank before hand but what are your thoughts on this?

 

Thanks in advance

[John Orentas]

Hi Liam.

 

After you have gone to all this trouble, think seriously about modifing your fuel system to a 'circulation' type, (if it isn't already) a bit like modern cars and racing cars.. Arrange things such that there is a constant circulation: Tank, filter, lift pump, injector pump, return to tank.

 

With this system your fuel system is constantly cleaned and you will never get that build-up of sludge in your tank or anywhere else.

 

Most modern engines are supplied new in this format but for reasons known only to themselves some engine installers choose to pipe things in the old fashioned way.

[Liam]

Hiya John,

 

As it is at the moment, the engine is in it's own room and mounted centrally. The diesel tank is down the left hand side of the engine and the batteries are on the right. The fuel line runs from the top of the tank, over the top of the flywheel cover, and then into the fuel pump on the opposite side of the engine. From there it goes into the fuel filter, and then into the injectors. The fuel return pipe is simply from the top of the filter directly back into the top of the tank again next to the fuel intake. All of the hoses are reasonably short as they don't go have to go that far to where they need to be. I think the longest one is fuel tank to fuel pump which is about 3ft long.

 

I'm not sure what you mean exactly by a circulation type fuel system?

 

We have though about, and are probably going to look into fitting a second filter between the tank and the lift pump itself. What are your thoughts on this?

[John Orentas]

Hiya John,

 

As it is at the moment, the engine is in it's own room and mounted centrally. The diesel tank is down the left hand side of the engine and the batteries are on the right. The fuel line runs from the top of the tank, over the top of the flywheel cover, and then into the fuel pump on the opposite side of the engine. From there it goes into the fuel filter, and then into the injectors. The fuel return pipe is simply from the top of the filter directly back into the top of the tank again next to the fuel intake. All of the hoses are reasonably short as they don't go have to go that far to where they need to be. I think the longest one is fuel tank to fuel pump which is about 3ft long.

 

I'm not sure what you mean exactly by a circulation type fuel system?

 

We have though about, and are probably going to look into fitting a second filter between the tank and the lift pump itself. What are your thoughts on this?

 

 

Hi Liam.

 

I think you already have a circulating system, but yes you can't have too many filters, the conventional way these days is to have a pre-filter immediately after the tank, then onto the lift pump input, output to the fine cartridge type filter / water trap, to the injector pump and return to the tank.. The drain from the spill tubes can go virtually anywhere into the circuit.

 

There can be variations in all this but the thing to remember is that the fuel must constantly return to the tank, you can usually hear it splashing in when you operate the lift pump, bear in mind to that the injector pump does not need any kind of pressure on it's supply, more a question of making the fuel available.

 

As an added bonus if you avoid 'dead ends' in the pipework the low pressure system will then be 'self bleeding'.

[smileypete]

Is there a need to be cautious regarding the sparks from say, a cutter mixing with the diesel in the tank? I suppose we could always pour some water into the tank before hand but what are your thoughts on this?

 

Good way to seriously injure or kill yourself...

 

cheers,

Pete.

[ChrisPy]

in an industrial environment you would need to 'inert' the tank before cutting. That is done by introducing nitrogen until there is only a small percentage of oxygen in the tank. Trouble is that nitrogen in a confined space (your engine room) could be dangerous for you unless you wear breathing apparatus.

 

I would drill a large hole and introduce a nibbler that will cut any shaped hole you want in steel up to about 6mm thick.

[howardang]

in an industrial environment you would need to 'inert' the tank before cutting. That is done by introducing nitrogen until there is only a small percentage of oxygen in the tank. Trouble is that nitrogen in a confined space (your engine room) could be dangerous for you unless you wear breathing apparatus.

 

I would drill a large hole and introduce a nibbler that will cut any shaped hole you want in steel up to about 6mm thick.

Just a word of caution if you drill the tank lid. Make very sure that you get rid of all the swarf.

 

Howard Anguish

[Liam]

Good way to seriously injure or kill yourself...

Could you please expand on that one... ?

 

 

in an industrial environment you would need to 'inert' the tank before cutting. That is done by introducing nitrogen until there is only a small percentage of oxygen in the tank. Trouble is that nitrogen in a confined space (your engine room) could be dangerous for you unless you wear breathing apparatus.

I would drill a large hole and introduce a nibbler that will cut any shaped hole you want in steel up to about 6mm thick.

What we plan to do is to drill four holes in the steel, and then use either a cutter or a jigsaw or something along those lines to make the hole, if you like. I'm only guessing that it's 6mm thick steel, as there's no edges or anything which are exposed to measure but it certainly doesn't sound, or feel more than 6mm when you're stood on it.

 

 

Just a word of caution if you drill the tank lid. Make very sure that you get rid of all the swarf.

 

Howard Anguish

Thanks Howard. Once we've drilled the tank and have the inspection hatch, we'll be able to access the tank properly and give it a good clean out.

[dacaB]

It occurs to me that a bit of research is necessary first. If you could buy a 'fitting' that is a screw access hatch then the job would be comparatively simple. ie: mark the hole using the 'fitting' as a template, cut the hole and drill the fixing points, bolt in the surround, permanantly, screw in the inspection hatch, not forgetting to clean out all the nasty first.

 

Maybe a nice shiny brass jobby............ big enough to allow you to get a hand, an arm, a torch and some rag thru the hole and still be able to see what your'e doing

Edited November 13, 2007 by dacaB

[smileypete]

Could you please expand on that one... ?

 

The cutting torch may ignite flammable fumes and air in the tank and cause an explosion.

 

I'd try some extra filtration and fuel additive first.

 

cheers,

Pete.

[Liam]

We wouldn't be using a cutting torch and definately no naked flames. Something along the lines of this...

 

[Yoda]

If you wish to cut into your diesel tank then do it when it's drained on a cold day and make sure you have a fire blanket with you.

 

Drilling and cutting can ignite the contents but they will only burn (relatively) slowly. There is more chance of swarf getting into the fuel system than a fire so you will have to weigh up which you can deal with the best. When you have it opened up make sure to give the tank and then the whole system a good clean and filtering.

 

I cannot commend this activity.

[Liam]

Thank you. I might give this a second thought now.

[bottle]

Liam

 

Something like this Nibbler would probably do it but as it names implies it 'nibbles' the metal away, lots of bits of metal into the tank (magnet to remove) and a bit of practice before use would be required to get a straight cut.

 

This one will only cut metal up to 3.2mm though. Probably best to hire.

[smileypete]

We wouldn't be using a cutting torch and definately no naked flames. Something along the lines of this...

 

 

Gawd!

[onthecut]

Crikey Liam -----

 

 

Sparks, carborundum dust, swarf -- you'll have a hat trick of nasties with that grinder, plus sparks showering alll over the engine room and batteries -- don't go there !! As Chris says, I'd go for one drilled hole, but then I'd look at using an air hacksaw (If you can arrange a compressor). Use a quality blade, smear it with grease to help trap swarf and off you go. Don't try and rush it and it will do a nice job for you.

 

Mike.