Fuel Tanks

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    Posted: 07 Apr 2019 at 5:44pm
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Somebody has advised me that steel fuel tanks need to be kept topped up because of the condensation/water issues
I was talking outboard engine not diesel with him so is this really an issue all the time or more in hotter months ?
And what about underfloor tanks that aren't steel is there still the same issues
Apologies if this has been covered recently, didn't see anything in quick search
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr 2019 at 6:38pm
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This was covered a few yrs back quite a few from memory, so may time ti bring back up
Condensation requires moist air.

The common thought is that as ambiant temp changes.. Ie say 5 deg at night and say 25 degs day in the sun.. It will suck air In over night.
But what happens is even at low temps the vapour pressure of fuel is still to great and the fuel will still evaporate faster than any air that will get sucked in.
This is also substantuated that dropping a match in a tank it will explode. That's a myth because that would require air in the tank.. A lot of air.. And to collect any significant moisture one hell of a lot of air.

The most common issue of moisture in under floor tanks is due to a poor or non existence of the O ring on the filler cap. Water rain, or waves, sits inside the cap then leaks past down into the tank.

Good practice is to fill up on the way to the ramp.. This mixes good fresh fuel into the older more stale fuel.


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Post Options Post Options   Likes (0) Likes(0)   Quote Photofisha Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr 2019 at 6:50pm
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Interesting info thanks for your reply
So is there any merit in filling your tank full when it’s being stored for any length of time because of the reduced air in tank
Fuel degrades overtime so that has to be taken into consideration also, from my side of things be using the boat all year round but always more rest days in winter ☠️
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2019 at 11:24am
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There is no air in the tank.. There is fuel vapour.
If ca car that is regularly used always has the tank full as practically possible.. It will have a very small increase in economy over letting the light come on then fill.
It is a slight.. Not signicsnt.
A classic car hot rod or a boat that is only used occasionally, eg say put away for the winter, come out late spring, should have min fuel in the tank.
It is not uncommon to have starting issues due to the more voiltile components of the fuel to evaporate off. It is these components that make starting easy.
By having the tank low.. Then filling right up the degraded fuel is diluted many times over and when the. Ix gets to the compustion chamber it fires up easy
A tank that is stored full will still loose these higher voiltile components.
Also of note, in plastic type tanks these can permiate out between the molecules of the plastic.
A tank that is very near or Mt will have air in it.. And as a result is a potential bomb waiting for an ignition spark.
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Post Options Post Options   Likes (0) Likes(0)   Quote krow Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2019 at 4:36pm
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Originally posted by Steps Steps wrote:


But what happens is even at low temps the vapour pressure of fuel is still to great and the fuel will still evaporate faster than any air that will get sucked in.
This is also substantuated that dropping a match in a tank it will explode. That's a myth because that would require air in the tank.. A lot of air..

A tank that is very near or Mt will have air in it.

Air or no Air? is this a bob each way?LOL
 
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Post Options Post Options   Likes (0) Likes(0)   Quote Photofisha Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2019 at 7:13pm
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