Fuel tank pressurising

[Yatesy350i]

Hi All

Can some one please point me in the right direction for this one please?

I've filled the car up today and never managed to get 50 quid in it before. But now as soon as I turn the ignition on petrol jets out of an overflow pipe behind the rear wheel arch. If I remove the filler cap the fuel will come back up the filler pipe and spill out?

Any ideas?

Cheers Karl.

[mrzigazaga]

Yatesy350i said:

Hi All

Can some one please point me in the right direction for this one please?

I've filled the car up today and never managed to get 50 quid in it before. But now as soon as I turn the ignition on petrol jets out of an overflow pipe behind the rear wheel arch. If I remove the filler cap the fuel will come back up the filler pipe and spill out?

Any ideas?

Cheers Karl.

Hi Mate...This happened to me one morning..I had a faulty seal on the filler cap, Which is non-vented..However yours sounds like a restriction somewhere..I believe the fuel system to be closed loop type..The atmospheric breather works as a pressure relief and also an anti-vacuum which builds up as the fuel drops..The pressure build up inside the tank should come out via the breather at there rear of the car...Don't start the car..Remove the filler cap and blow up the pipe if you can to see if it is clear...There might be petrol sitting in it that is acting as a stop..Although it should either be sucked back or out with pressure but it could be enough to start a syphoning motion although I'm sure it shouldn't...Ziga

[ElvisWedgely]

I've had a similar problem before when I filled the tank right up to the top and when I moved the Wedge a short distance a lot of petrol started to over flow near the rear wheel arch on the passenger side where the overflow is. The Wedge has two tanks connected in the middle by pipes. Somehow overfilling doesn't go down too well, so I never overfill the Wedge, even on a long journey. Always three quarters full.

I dont know why it would overflow when the ignition comes on though. That sounds a bit weird, unless it's leaking elsewhere when the ignition is switched on.

Tony.TCB.

Edited by ElvisWedgely on Friday 11th April 14:26

[digga951]

Mine does this too... very annoying!

I've never been able to solve the problem, but my theory is that the cold fuel expands once it warms up inside the tank, especially as it has the exhaust running underneath it. The excess then comes out of the tube which runs from the filler neck, through the boot where the hinges are and then down to just behind the rear nearside wheel. Opening the fuel filler seems to have the same effect - lots of fuel pouring out.

I just make a note to not over fill it now, and especially not if I'm going to do a short journey or park up for a while soon after filling.

Dan.

[Yatesy350i]

digga951 said:

Mine does this too... very annoying!

I've never been able to solve the problem, but my theory is that the cold fuel expands once it warms up inside the tank, especially as it has the exhaust running underneath it. The excess then comes out of the tube which runs from the filler neck, through the boot where the hinges are and then down to just behind the rear nearside wheel. Opening the fuel filler seems to have the same effect - lots of fuel pouring out.

I just make a note to not over fill it now, and especially not if I'm going to do a short journey or park up for a while soon after filling.

Dan.

Thanks Dan

And the rest of you for that matter. I've just tried the return to rank line running into a petrol can and then flicked the ignition on. Pump runs fuel returns to can no fuel coming up the filler. So as you say it's ne of those quirks or there is a problem with fuel or air transfer between the tanks?

Is it worth perusing this further or should I just drain some fuel and accept it as the norm?

Many thanks Karl.

[mrzigazaga]

It does sound like its a matter of you overfilling...If you have ever syphoned petrol from a car before then you will know that once it starts flowing it will continue to do so until interrupted ...This may just be the case.

If there is an abnormal pressure build up due to the breather being blocked then you would experience a large pressure release when you remove the filler cap...
I do recall when this happened to me the car was parked on a camber O/S in and it poured out the filler cap down the side of the car and along the sill as i turned it on..However the day before i did overfill....Ziga

[V8 Fettler]

Is this related to the recent warm weather? Wedge twin tanks are a bugger to get rid of airlocks, trapped air is cool when tank is being filled, soon warms up in the sunshine and expands.

Strange hip motions required against the side of the car when filling. Some of the older contingent might recall "The bump" circa 1974.

Don't "brim" it unless driving some distance immediately.

[wooly350i]

From a plumbing perspective in relation to air locks its important to allow pipes to drop all the way to the pump without deviating upwards, the same applies to the pipes linking the tanks , I've seen them kinking downwards because the pipe may be too long, would be better to kink sideways than vertically , air locks can occur easily in pipework that raises and lowers and is a bugger to get rid of when relying on gravity as the connecting pipes between the tanks don't benefit from the pump pressure.
Just my two pence worth of bks, wooly.

[Yatesy350i]

Removed a few litres of fuel. No more problems.

Cheers Guys