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Old 12 June 2016, 02:54   #1
Country: UK - England
Town: Sandy
Make: Zodiac Cadet 285 FR
Length: under 3m
Engine: Mercury 6HP
Join Date: Apr 2015
Posts: 11
Plastic fuel tank question


In recent changeable weather I've noticed that a plastic fuel tank (12.5l genuine Mercury), part filled and stored in a garage some way from the house, has its sides collapsed in after a cool night, and bulges at the end of a warm day.

When the sides cave in there are quite sharp creases at the tank's corners.

Will this happening repeatedly weaken the tank?

How do you avoid it?

I've considered leaving the air vent open but there's a safety issue with that if. Vapour escapes.



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Old 12 June 2016, 03:29   #2
Country: UK - England
Town: East Anglia
Boat name: Nimrod II
Make: Aerotec 380
Length: 3m +
Engine: Suzuki DF20 EFI
Join Date: Nov 2007
Posts: 3,599
Pete you have to make your own choice here.

I've seen the most dramatic sucking in and bulging out of tanks over the years so I now garage store them with the vents cracked a tiny bit. The garage is well ventilated, cool and not connected to the house. I never smell any fumes from the tanks.

When travelling the tanks I always do the vent up tight.

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Old 12 June 2016, 03:38   #3
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Country: Ireland
Make: Redbay Boats
Length: 9m +
Engine: 370hp
Join Date: Feb 2008
Posts: 13,094
Pete - good advice from Fenlander there!

Chances are you already have another vented petrol tank in that shed - think lawnmower. The vent should be opened only the VERY smallest amount (do this when it's under slight pressure and as you open it you can stop at the very first release). This will allow equalisation but very little petrol vapour will follow after that. Logic says to store the tank in the coldest lowest part of the shed out of direct sunlight and away from sources of ignition (heaters, furnaces, switchgear). I keep mine beside my DIY cider "cave" - what could possibly go wrong?
"Who knows what evil lurks in the hearts of men?"
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Old 12 June 2016, 04:06   #4
Country: UK - England
Town: Sussex
Boat name: Bombard, Y-162
Make: Aerotec 380, Y-Class
Length: 3m +
Engine: Mercury Mariner 15hp
Join Date: Jul 2010
Posts: 2,784
They usually inflate/deflate a little but should not be much unless you are leaving them in somewhere with larger temp differences, if you are seeing sharp creases that is surprising as normally the material is quite stiff. Less petrol in there the worse it is.
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Old 12 June 2016, 11:26   #5
Country: UK - England
Town: Retford
Boat name: Spy-sea-one
Make: Mercury
Length: 3m +
Engine: Suzuki Outboard/25/4
MMSI: 235074042
Join Date: Oct 2011
Posts: 3,822
The only reason the tank has a breather screw is because the fuel is so close to the top of the tank and has be shut for transportation. in use bouncing about in the boat you can get a slight bit of spillage but nothing to worry about to be honest I don't shut mine unless their full and transporting to and from ( when open just cracked).
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