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Getting fuel out of an underfloor tank

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Post Options Post Options   Likes (0) Likes(0)   Quote Dagwood Quote  Post ReplyReply Direct Link To This Post Topic: Getting fuel out of an underfloor tank
    Posted: 15 Jul 2022 at 8:14am
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Looking to get the fuel out of an underfloor tank (yes it's my boat!) to use in the car and replace with fresh stuff.

Syphoning won't work that well - not enough height.

The outboard draws it up through a water separator / filter so I'm thinking of a fuel line with the same fitting and a 12 volt pump and I can pull it through this filter which is an added bonus.

Has anyone done something similar? - if so what sort of pump did you use? 
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Post Options Post Options   Likes (0) Likes(0)   Quote gkd@igrin.co.nz Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2022 at 8:32am
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How big is the tank? Where is it located? Take off filler hose, put syphon hose thru bung hole and info tank
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Post Options Post Options   Likes (0) Likes(0)   Quote Dagwood Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2022 at 8:57am
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About 80 litres under the floor of a 530 Stabi. The filler and feed hoses are sods of things to get on and off (thick walled and short runs.
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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2022 at 9:20am
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I presume you can't take the tank out or is it just too heavy with the amount of fuel in it?
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Post Options Post Options   Likes (0) Likes(0)   Quote Dagwood Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2022 at 9:51am
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Originally posted by smudge smudge wrote:

I presume you can't take the tank out or is it just too heavy with the amount of fuel in it?
Nah , all welded in... 
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Post Options Post Options   Likes (0) Likes(0)   Quote Dagwood Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2022 at 10:17am
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Thinking that something like this might work but not sure if it'll cope with a smaller diameter hose and the restriction of the filter...
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Post Options Post Options   Likes (0) Likes(0)   Quote Malcolm in the Middle Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2022 at 4:02pm
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How old is the fuel, and how full is the tank?

My outboard mechanic advised you can often get away with topping the tank with a bit of high octane fuel (yep the extra expensive stuff). This will help replace the overall octane which reduces  as the fuel ages.

Also depends on what you are going to use the motor for. If skiing (not likely this time of year) you will want best octane, but if cruising then not so crucial


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Post Options Post Options   Likes (0) Likes(0)   Quote Bounty Hunter Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2022 at 9:18pm
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you could get one of these;



obviously going to be a little bit of shagging around removing 80 odd litres - but they are useful to doing your own oil changes in the future

No disintegrations!
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Post Options Post Options   Likes (0) Likes(0)   Quote FarmerBrowne Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2022 at 9:56pm
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Purchase 2 metres of outboard motor fuel line - same diameter as the fuel line from the water filter to the outboard motors filter.  Disconnect where the line joins the outboard filter and connect to the 2 metres of fuel line (the piece of pipe on this sprayer (www.mitre10.co.nz/shop/number-8-pressure-sprayer-5-litre/p/234818) generally fits inside the fuel lines and can be used to connect the two pieces of fuel line together).  put your empty fuel container on ground behind boat.  Use the manual fuel pump to get fuel started flowing and once started it should continue to syphon on its own till tank is empty.  Generally takes around 20 minutes for 20 litres of fuel.

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Post Options Post Options   Likes (0) Likes(0)   Quote MarkE Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2022 at 4:33pm
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Originally posted by Dagwood Dagwood wrote:


Syphoning won't work that well - not enough height


cant you just tow boat to a higher spot and then syphon? seems like the easiest solution...
Sea Strike 18' Centre Console - Under Construction....Build Thread here
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Post Options Post Options   Likes (1) Likes(1)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2022 at 5:26pm
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Dagwood, if the fuel isn't 'too old' I would add some higher octane fuel (if it's say half full). An alternative would be to add an octane booster. Outboard motors have a relatively low state of tune  compared to a car. 

I presume it is a four stroke? Two strokes have a  low compression ratio compared to a four stroke and are much more forgiving around octane ratings. My mate left his boat at my place for over 2 years (it was a  carbureted 140hp Mariner2 stroke) and we went fishing one day and it didn't miss a beat in 2 hours of motoring. It had a full tank when he stored it here which helps. If you're using Gull fuel water absorption may be an issue. Small quantities go 'off' faster but unless your boat has been sitting for 6 months or more on a  half tank or less I wouldn't be too concerned. 

Having said all that I'm not a mechanic.
Best gurnard fisherman in my street
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Post Options Post Options   Likes (0) Likes(0)   Quote Kandrew Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2022 at 6:01pm
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That’s a good idea, like a driveway with a retaining wall.
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Post Options Post Options   Likes (0) Likes(0)   Quote Kandrew Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2022 at 6:26pm
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The problem is when petrol gets old it losses it’s ability to hold the oil in suspension which can be fatal for 2 stroke.

This pump looks good might buy one myself

https://www.repco.co.nz/en/4x4-adventure-escape/travel-touring/jerry-cans/mechpro-blue-battery-operated-electric-siphon-pump/p/A6117722?rgfeed=true&cid=google-shopping&utm_source=google&utm_medium=cpc&gclid=EAIaIQobChMIjIXRz-L8-AIV4JpmAh1W8QNjEAQYASABEgIUbvD_BwE

I’ve used these types of pump before as well.

https://www.topmaq.co.nz/drum-pump-auoi1650?gclid=EAIaIQobChMImdWE0eP8-AIV15lmAh1SzgYhEAQYBSABEgJW2vD_BwE
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Post Options Post Options   Likes (0) Likes(0)   Quote Dagwood Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jul 2022 at 2:53pm
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Thanks for the suggestions guys, some stuff to consider here...
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Post Options Post Options   Likes (0) Likes(0)   Quote Dagwood Quote  Post ReplyReply Direct Link To This Post Posted: 17 Aug 2022 at 8:36am
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Just an update for anyone interested. 

My outboard is connected to the fuel separator via a standard female tote tank fitting. This allows me to connect it to a separate tote tank I carry on board for an emergency / reserve.

I went out and bought another female fuel fitting, fuel line and a 12v fuel pump from Trademe ($20.00). Using a cigarette lighter connection and an inline switch I had in the box of "S%^t that might be useful one day" I assembled everything and mission accomplished!

Fuel is pulled through the filter and water separator at a rate that would allow this to work effectively and can be put into a 20 litre jerry can outside of the boat (fumes and spillage). It would take 15 - 20 minutes to fill so easy to potter around doing other jobs while keeping an eye on it. Self priming, no mess, no risk and no need to suck petrol fumes.

Can now easily cycle it into the car before there's a risk of it going bad with min effort.. 
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