Air in fuel tank

Most cars I have owned, have had a small hole in the filler cap in order to prevent a partial vacuum as the fuel gets used.When I remove the filler cap on the Exige, it sucks in air like a Beirut street walker. This is a bit worrying. Apart from placing an increasing strain on the fuel pump as the fuel level decreases, it must be continously flexing the fuel tank’s walls.Any ideas anybody?

Hmm… I have the same thing.Although, my Impreza does the same thing if more than half empty.Could give Lotus Technical a call and find out ?

Could you please?

I read somewhere (in the manual?) that the fuel tank is pressurised and I always thought it was this pressure that was causing the air rush. Could be easily wrong though (my memories getting worse now I’m the wrong side of 30).

This is in fact normal for modern vehicles. Legislation prevent petrol tanks from being vented to the atmosphere, they are now vented through the engine via a charcoal canister, this only happens very slowly hence when you open the tank, sometimes you hear the air rush in. Of course this venting through the engine has a downside on performance, and if you look at the posting make about getting 340bhp/tone from a 340R you will see a section on removing the charcoal canister, and venting the fuel tank in the normal way. Hope this helpsChris.

Regarding the pressurised fuel tank, Hitch is probably confusing it with Lotus’s warning that the fuel line between the fuel pump and injectors remains pressurised at all times and needs to be depressurised before doing any work on the fuel system.The reply by H15EXG seems to suggest that it may be prudent to undo the fuel filler cap every now and then to stop the fuel pump from having to struggle against an increasing ‘pull’ from the fuel tank side. Under certain conditions (near empty tank, big throttle) it could lead to fuel starvation, because the pump is required to deliver max fuel (push)against max vaccum (pull).

I think you will find the fuel pump is more than capable of supplying the fuel, regardless of the amount of fuel in the tank or the throttle position. I just find the sucking in of air when you open the fuel cap a little disconcerting. Chris.