Water in Fuel Tanks

[4129R]

Has anyone else experienced water in the fuel tanks?

The water sinks to the bottom, so not much in the tanks will be sucked into the fuel pump and stop the engine from running, and it will spread into both tanks if only 1 is leaking. 

I have checked both tank tops, and neither is leaking. There was about 2 pints in the tanks after the car was standing for about 9 months.

The filler caps are tight and the rubber connectors to the tanks are both new.

Is it just condensation in a damp climate? 

[Kendo]

That is a lot of condensation in nine months. How would the damp air get in the tank? Does it have vents open to the air? (No filters on them?) Could the water have been there nine months ago? Contaminated gas? I’m in arid California, so little recent experience with humid environments.

[4129R]

That is a lot of condensation in nine months. How would the damp air get in the tank? That is exactly what I cannot understand.

Does it have vents open to the air? The tube to the long filter is not there and like most cars, that long filter side to side went years ago
(No filters on them?)

Could the water have been there nine months ago? No the tanks were fitted completely dry.

Contaminated gas? No, 20 litres of super unleaded fuel was poured in from a jerry can, and carefully checked before it went in.

I’m in arid California, so little recent experience with humid environments.

In the UK, we have had the wettest 18 months on record.

[Grumblebuns]

Isn't there a overflow vent in the filler neck just below the grommet? If its open to atmosphere, the constant change in temperature over time will cause the tanks to "breathe". Is that enough time to cause all of that condensation you are experiencing?   

[Kendo]

That’s the vent I was thinking about. I imagine it would depend on how full the tanks were, how much air volume could change with each “breath”. Another thought, are there gas formulations that like to absorb moisture from the air?

[SwiftDB4]

Alcohols like ethanol absorb more water than straight gasoline.

[Grumblebuns]

I don't know the ethanol percentage in the UK. Do they even use ethanol over there?

[4129R]

I have to use Super Unleaded, rather than normal Unleaded, which has a larger alcohol content. E5 petrol is made up of 95 per cent unleaded petrol plus 5 per cent ethanol (which is why it’s named ‘E5’). E10 petrol is much more beneficial to the environment, containing 10% ethanol and 90% regular unleaded petrol – and was introduced to help the government meet its climate change targets.

The breather hole in the filler neck is very small.

If the fuel was hydrophilic, it would absorb moisture from the atmosphere.

I just cannot see how so much water gets into an apparently sealed pair of tanks except for tiny breather holes which point 45' down. .