Emptying an underfloor tank

Gday team. So the past couple day I took the dog and we spent a night down at the boat just pottering around and doing a few jobs on the boat while we were there. The boat has two stainless underfloor tanks. The rear one is shorter than the front one, but deeper and holds about 70 litres. The one in front of it is not as deep due to design of the boat but is really long and I estimate it will hold around 130 litres. They are completely independent of each other with a couple of taps in the transom to switch from one to the other. The old owner had always only used the rear one, and untill now we had also only used the rear tank. I wanted to run the boat on the front tank as it will be handy for longer trips having them both full so I three 75 litres of fuel into it (bloody hell fuel is expensive now!) And switched the tanks and primed it up. Got halfway out of the marina and alarm started going off for fuel/water separator on the engine. I switched back to the back tank and limped back quietly to our berth. Took the fuel filter off the engine and tipped it out and it had a lot of water in it, I have had the floor up before and from what I could tell the tank seemed and sounded completely empty. I took the fuel delivery off the outboard and switch back to the front tank and primed some fuel through again into a bucket and there's a lot of water in it! I'm not even mad that there's water in there, I should have checked better... I am mad that it's now mixed with $200 worth of fuel!
I've resigned myself to the fact that the tank is going to have to be flushed out. It will be very tedious process trying to pump the entire tank empty using the primer bulb. Any one got any flash ideas to make the job quicker/easier? I thought I might flush it all out then put 20l or so of diesel in it and try rock the boat round a bit and flush that through also before trying to flush any fuel through, I could then put say 20 litres of fresh premix petrol in it and run it through my wee aux motor, 20hp two stroke Merc which will probably eat up any impurities better than the injected motor will.

Diesel won't work. Used methylated spirits.

The water won't be mixed with the petrol,it will sit on the bottom,the tank should fall to the outlet.Keep pumping,should not be to much.
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Originally Posted by muzza

big arsed electric fuel pump - should suck though easily

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What he said.
And avoid sparks.

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Originally Posted by muzza

big arsed electric fuel pump - should suck though easily

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Yea I was just thinking I have a couple of Cdax 12v sprayer pumps I could probably rig one of them up to the end of the fuel line and suck it through

Sounds like you have a good plan. Don't get too carried away though. Once you have emptied the water as much as possible and cleaned up with the meths just keep an eye on your water separator/filter. You'll always have some water in those tanks. Best way to stop the condensation is keep them full.

put an airline into the fill hole, with a rag tightly bunged in (and around the airline) to seal it off.
Turn the air on and it will blow it all through.
If you want to syphon it out through the fill hole, then put a hose down to the bottom of the tank as well as the air line.
Works well for syphoning fuel instead of sucking a mouthful, Just blowing into the tank with another hose is enough to start a syphon.

To be fair you could probably just drain the water and carry on without dropping all the fuel and flushing the tank. Keep a spare filter handy and keep emptying the water bowl.

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Originally Posted by Hahn

To be fair you could probably just drain the water and carry on without dropping all the fuel and flushing the tank. Keep a spare filter handy and keep emptying the water bowl.

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I reckon.
So long as it is only water and no sediment etc.

the feul can be used on low importance things so it dosent go to waste once it has settled and you syphon out all the water/crud

think lawnmower for petrol (quads handle it quite well too)

and shittly ol tractor for diesel

not airplanes or boats as its a bit hard to walk home

Id go back to just using the clean tank and above floor (20l containers) storage

C Dax pumps work great, really easy to set up safely. And then to be sure, put in a litre of meths with the first full tankful.

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Originally Posted by Husky1600

C Dax pumps work great, really easy to set up safely. And then to be sure, put in a litre of meths with the first full tankful.

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why the meths mate?

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Originally Posted by Bill999

the feul can be used on low importance things so it dosent go to waste once it has settled and you syphon out all the water/crud

think lawnmower for petrol (quads handle it quite well too)

and shittly ol tractor for diesel

not airplanes or boats as its a bit hard to walk home

Id go back to just using the clean tank and above floor (20l containers) storage

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Be cool to get that extra tank going though. Pain in the arse having the floor cluttered up.

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Originally Posted by Bill999

why the meths mate?

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Meths is hydroscopic and attracts water. It also burns cleanly so won't damage the engine. if the water is in a mist it goes through the engine ok. mates have had water/meths spray set ups for boosted cars

You'd be surprised how much water is in aircraft fuel tanks, especially in humid climates. A trick I was taught learning about water testing was when you have your bucket of fuel and it looks clean spit in it. If it sinks you have clean fuel. If it disappears you have a bucket of water. You could still have entrained water, use these if you're worried. shell-water-detector-kit/ draw the fuel through with a syringe.

the whole meths thing really is a big fairy tale, to confirm this for yourself chuck a litre of fuel into a glass bottle and however much/little water as you want, add meths and watch nothing happen.....yeah sure if you agitate it the water breaks down briefly and cant be seen but give it a minute and it reforms, it'll do this without meths anyway
Water in marine engines, even as a mist is not a good thing, its used in drag cars etc as a mist into engine as water will not compress and can be used to increase engine compression/generate more power, not a common practice for anything you want to last any period of time tho

When draining fuel tanks on trailer boats i always run a fuel hose from the outlet side of water separating filter down to bung hole and exit boat to jerry cans etc and siphon that way, checking/draining filter regularly, and remember that however a tank is siphoned there'll always be dregs you dont get so ALWAYS check the filter pre trip
Goes without saying filter should be replaced once tank drained as much as possible

Drill pump?

https://www.trademe.co.nz/a/marketpl...0?bof=TYnYGhGt

Just did a mates boat, used an air diaphragm pump and pumped the shitty fuel into plastic cube tank, filled it up with clean fuel and he away boating.
Used a small dia/length of electrical ducting as a suction dropper.

Air diaphragm pumps are good.
No sparks, no fumes and work under water.
We use them to pump out flooded sumps/pump rooms.
No worries of running dry.

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Originally Posted by Grasshoppa

the whole meths thing really is a big fairy tale, to confirm this for yourself chuck a litre of fuel into a glass bottle and however much/little water as you want, add meths and watch nothing happen.....yeah sure if you agitate it the water breaks down briefly and cant be seen but give it a minute and it reforms, it'll do this without meths anyway
Water in marine engines, even as a mist is not a good thing, its used in drag cars etc as a mist into engine as water will not compress and can be used to increase engine compression/generate more power, not a common practice for anything you want to last any period of time tho

When draining fuel tanks on trailer boats i always run a fuel hose from the outlet side of water separating filter down to bung hole and exit boat to jerry cans etc and siphon that way, checking/draining filter regularly, and remember that however a tank is siphoned there'll always be dregs you dont get so ALWAYS check the filter pre trip
Goes without saying filter should be replaced once tank drained as much as possible

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I agree re meths absorbing the water.

I did an experiment where I nearly filled a two litre Coke bottle with petrol then topped it up with some and added a fair dash of meths - and shook the bottle to blazes, the petrol etc all mixed into a murky fluid but twenty minutes later it had settled into three distinct levels like a fancy cocktail.

Maybe I was expecting too much and had more water than the meths could handle or something - but that was MY experience with this theory.

You can buy water absorbing "chemical socks" , put them in, let then settle to the bottom, take them out - they will.be quite swollen. I don't know the proper name for them sorry but I've used them on tractor and digger tanks here.

The methanol in methylated spirits can make small amounts of water miscible in the fuel. It can probably only deal with low levels of contamination. Using meths has definitely saved my arse a couple of times with water in fuel in old carbed cars. Fuel injected petrol engines can cope a little better with small amounts of water contamination. There are concerns about E10 fuel which contains ethanol causing problems in older outboards so I still would not use meths as if alcohol remains in the system over time it can apparently degrade rubberised parts like orings and affect some plastics.

I'd be more concerned about the source of the water for the future. Could the tank breather be letting water in somehow? Is there some way water could get in through the fuel filler hose or cap. Could condensation be an issue through big temperature changes/low fuel levels for extended periods in the tank? I run one of these these so it's easy to dump any water rather than biffing the whole filter cartridge and you could use two in series preceded by a primer bulb to halve the load if problems persisted

Oo always wondered where to buy these kits from. Very handy for cloudy ago

Where did you get the fuel from?? its not an uncommon thing for the fuel to be contaminated at the pump. I've towed lots of cars with water in the gas after they gassed up.

Petrol or Diesel its mostly fatal to these new fuel injection pumps and systems. Esp common rail diesel. Any water in there and its history.

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Originally Posted by tac a1

Where did you get the fuel from?? its not an uncommon thing for the fuel to be contaminated at the pump. I've towed lots of cars with water in the gas after they gassed up.

Petrol or Diesel its mostly fatal to these new fuel injection pumps and systems. Esp common rail diesel. Any water in there and its history.

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And yet you see the pathetic sieves they install as fuel filters in modern cars. FFS, a few drops of water in a common rail and it 10-12K worth of damage. How about actual, proper water separators and 2 micron filters??

Fuel Doctor was made for this scenario and works a treat if its to much of a prick taking the outlet off the tanka nd using the fuel pump to drain the tank into a suitable container
a decent water separator/filter should be next on the shopping list
https://www.supercheapauto.co.nz/p/f...070201#start=2

This is a common problem on moored boats. Best (but sorta expensive) way to mitigate it us to keep the tanks full - this prevents the condensation that produces the water.

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Originally Posted by Tentman

This is a common problem on moored boats. Best (but sorta expensive) way to mitigate it us to keep the tanks full - this prevents the condensation that produces the water.

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And any steel farm tank. I have an old 1000L tank, the mechanic in me hates the idea of the rust and water forming inside it, but keeping it full defeats the purpose or having it. Two good quality filters give piece of mind especially when it empties and you see how much rusty sediment is caught by the first filter/water bowl.

If you have fuel, you probably have water. A drain tap on the lowest part of the tank is really the best solution if it's going to be a while between trips if that's possible. Otherwise just keep good quality filters and emptying the separator bowl.

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Originally Posted by Ryan_Songhurst

Yea I was just thinking I have a couple of Cdax 12v sprayer pumps I could probably rig one of them up to the end of the fuel line and suck it through

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If it's a short exposure to petrol you'll probably be OK, but just be aware that hydrocarbons are unforgiving to elastomers / soft polymers that are not rated for them. I don't think the sprayer manufacturer would have had petrol/oil/diesel in mind when specifying the pumps for their application.