gas tank condensation

Winters nearly here - a full (aluminium) gas tank needs preserving for warmer weather . . .
Well, the 27 foot powerboat is not quite finished yet and I understand wise advice not to foam in the tank - so it will be strapped onto neoprene faced drainage slats. Full air circulation.

However, would polystyrene foam insulation sheets dropped down the sides and placed on top not prevent the tank sides getting cold enough to allow internal condensation?
Or does that condensation come from somewhere else?
(petrol is bloody expensive here!)

 

In Alaska I had plenty of Condensation in the Tanks. All of them.
Anywhere the Warm meets the Cold, condensation will form.
The Tanks in my Fiberglass 27' were glassed or foamed and they rusted.
The Tanks in the Pickup, Snow Blower were in the open air and they picked up water as well.
Even the underground tanks had Condensation.
I don't think you can keep condensation out of the tanks. You probably couldn't afford it in a small boat any way.
For mounting Tanks, Straps are better than foam if you can support the weight adequately.

 

Either keep the tanks full or completely empty and ventilated while stored for the winter.

-Tom

 

I agree, we keep our tanks full all winter and never have trouble with condensation. One guy told me that he connects an expansion bottle with T connection to the went hose and the he closed the end of the went to prevent change of air in the tank from outside. Sounds kind of dangerous, if you forget to open the went when you start the engine.

Axel

 

Thank you gents.
I just wondered whether you might have experimented with some form of blanketing to insulate the tank. Particularly aluminium which transfers temperature so quickly?

 

When I flew ultralight aircraft we all used plastic jerry jug like gas tanks and were initially very concerned about condensation but it just never happened. Over 20 years of flying and nobody that I know of ever had a problem. I installed new aluminum diesel tanks in my Willard and have had almost no water in them either. This winter I'm going to leave the tanks half full and take samples to see how much water forms in the tanks.

 

I keep aluminium fuel tanks empty. Never had a water problem

 

Why worry about a bit of condensation in your boat's tank? Install a water separator and check the glass bowl regularly.

Most of the water originates from the underground tanks in the fuel station. I once was the first early morning customer in a marina and got more than two fuel filters/separators could handle.
The sad thing is that you pay gasoline prices for water!

 

Thank you very much for your advice gents, I shall heed it.
Alaska - lordy I thought it too chilly here in Blighty . . .

 

The temperature changes make a tank act like a pump. When it warms up, the air/gas mixture expands and vents out. When it cools, moist air gets sucked in through the vent.