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Subject: Fuel Tank Draining

Dear Tony

Have just had a central heating specialist examine heating on boat for 3 hours (in the rain!) He says he thinks the problem is contaminated fuel from the tank - the central heating fitting is leaking rusty coloured fuel when he takes it off. He has taken it for examination and should return it next week.

I'm a bit out of my depth with this. Will I have to drain the fuel tank? If so, how do I go about it and where do I get equipment from (or is there someone I can call to do this?)

Or is there anything else I can do to clear up the possible fuel contamination problem.

Many thanks Emma


Dear Emma

The answers to all this is "it all depends".

If the colouration really is rust, you should have a filter in the line (like the engine fuel filter) that should remove the rust particles. If the fuel is stained brown I fear its the dreaded diesel bug and that will be attempting to block the engine filters and fuel system as well as causing problems for the central heating system.

I assume we are talking a Wabasto/Mikuni/Ebbs type central heating system here, so I think you may have to drain your tank, change all filters and clean/purge the fuel lines. The new fuel will then need treating with a fuel additive. One with a biocide at first and after a few months I would prefer to see you switch to one that simply removes water from the tank.

Again you do not tell me what type of boat you have, but if its a narrowboat you can often get a pipe down the filler hole and use an electric or manual pump to remove all the fuel and water. Some NBs draw fuel from the bottom of the tank, so providing the tank is not under the engine or anywhere odd, simply undoing a suitable pipe joint would allow you to drain the tank into a series of containers.

I am sure any boatyard or engineer will be happy to do this for you - at a price.

As far as equipment is concerned, all you need is containers (4 or 6 pint milk bottles? - lots of them) if you do have a feed from the bottom of the tank.

If you have something to drain the engine oil, you might be able to adapt that to pump out the tank - eventually. You might also be able to use one of those pumps that fit onto an electric drill

You may even be able to hire a suitable pump, but as I say, it all depends.


Tony Brooks


NOTE recently I have tested a kit that is supposed to tell you how bug contaminated your fuel is. I fear it will tend to overstate the case, but this would give a fair indication about what may be wrong. The product is called Marine16, but may not be easily available yet.



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