Lotus Elan

Leaking tank or evaporation?

PostPost by: jensmartin » Wed Apr 10, 2013 7:40 pm

Hi all!

I filled the tank on my +2 -72 in december and measured the petrol level down the filler neck with a stick. 3,5 months later the level had dropped 5 cm (2 inches). No driving of course :) Is this a leak or could it be evaporation? Seems like a but much to evaporate to me?
For what I can see, without having tanken the tank out, I can find no signs of leaks anywhere.

Any ideas?

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PostPost by: bobm3142 » Wed Apr 10, 2013 9:59 pm

The rate of evaporation depends heavily on how much the tank is ventilated. If you leave the cap off it will evaporate fairly quickley especially if it is warm.

If the tank has a leak in the boot then you would smell it quite easily.

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PostPost by: Robbie693 » Thu Apr 11, 2013 12:31 am

Because of the size of the vent pipes, fuel in a Plus 2 evaporates a fair bit. It also smells a fair bit!

I'd bet on it being evaporation, if you have a leak it should be pretty obvious - stains on the garage floor, moisture around the tank, top of diff etc.

Some plug the vent tubes when not it use - do a site search for whiskey corks and you'll see some discussion about this very matter!

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PostPost by: Spyder fan » Thu Apr 11, 2013 9:41 am

Hi Jens,
I agree that it is evaporation rather than a leak.

Why did you fill the tank if you were not going to use the car, apart from the waste from evaporation the octane level of the fuel will have deteriorated by now.

Here's an interesting article from BP regarding storing fuel. It suggests leaving the tank half full if the car is not to be used for a while and that fresh fuel should be added before starting the engine.
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PostPost by: jensmartin » Thu Apr 11, 2013 5:18 pm

Very interesting reading Alan! Thanks alot. So probably it's not a leak I have.
The BP document states that after 5 week 15% of the volume is lost! Seems to explain my lost two inches of fuel.

I've been learned that you should let the tank be full to collect less water when stored for a long time, this seems to be wrong.

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PostPost by: rfurzer » Fri Apr 12, 2013 2:45 am

Not driven since December!

My +2 plots trouble if I leave her for more than a week or so.

The best place to lose the petrol is down the throats of the webers!

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PostPost by: peterako » Fri Apr 12, 2013 7:26 am

My +2 uses more petrol when stood still than when driving....

Evaporation...... :(

Would be more acceptable if the huge breathers actually allowed me to FILL the tank (tank evaporates less the fuller it is).

So, my solution is to drive it as much as possible.

It's more economical that way....at least that's what I tell 'er indoors...... :)

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PostPost by: h20hamelan » Tue Apr 16, 2013 12:37 am


I am planning on newer teflon lines combined with steel or... along the length or backbone. As well as fuel injection clamps.

Rubber does allow evaporation and so do the +2's vent system.

There are posts to using a modern fuel breather vent (internals of a gas cap) While using the flip lotus external. You need to remove the spring etc. But it has been working on my car.

vote for 1/2 full/empty then fill and start. run empty and fill with fresh fuel
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