Pressure In Fuel Tank

[MartinShorthose]

After I have driven for a few miles and stop to refuel, a seemingly huge amount of pressure is released as I remove the fuel cap.

Is this common or do I need to replace my fuel cap?

[ColinBarber]

That is normal

[redneck]

i asked a lexus dealer about it...it's a special "pressure release" system that's used

[maneesh]

Yes, normal, but can seem scary to those who don't know, particularly when the car has a very empty tank, considerable vacuum pressure builds up inside. They used to have a name something like "foo-foo" valve on old Toyotas which had a special valve to let the pressure out when you twist the cap. They used to call it a foo-foo valve as the hissing noise "used" to make a similar sounding noise.

Remember, you've got a large tank when empty (85 litres).

[redneck]

so definetely no smoking

[GreyBeard]

i think you'll find it's a vacuum, so unless you drop your fag in the tank, you should be fairly safe! and for the PC lot, you shouldn't be smoking at all when you remove the filler cap!

[paulydude]

I remember when this first happened to me. Blamed the wife!!!

[MartinShorthose]

Thanks for your input - it is definitely pressure and not vacuum!

[TonyGoose]

Thanks for your input - it is definitely pressure and not vacuum!

In that case hang on tight to the fuel cap.

Wouldn't want it launching off and taking someones eye out

[ROYT]

MY '94 LS does the same it's normal,I just unscrew the filler cap slowly.

My old Merc. and Honda did the same!

[Rob]

They used to call it a foo-foo valve as the hissing noise "used" to make a similar sounding noise.

LOL - a "foo-foo valve" is a common term used to describe something that doesnt really exist / name unknown etc only ever heard it in context to aircraft!

[d3fy]

Like Foo Fighter - UFO

[Steve]

i thought "Foo" was a term used by Mr T

[d3fy]

:D As in , ' I a'int getting on that plane foo' :D :D

Foo

[aido]

Foo

Some of those definitions are just mental!

And not quite on topic but yeah, my fuel cap makes the noise too - it's a good time to let one go and everyone just thinks it's the fuel cap

[ColinBarber]

http://www.lexusownersclub.co.uk/knowledge...x_v2&id=96&c=15

[davepruce]

Sorry Colin, I have to disagree!

On my LS400 '94, I have to hang on to the cap (a little exagerated but not much!) to stop it being blown across the forecourt. If it was a vacuum, then it would be difficult to remove the cap!

Surely the pressure is there to aid in petrol delivery to the engine, a partial vacuum would do exactly the opposite.....

Cheers

Dave

[ColinBarber]

I think the EEC system works differently on newer models which is what my link describes. On older systems the tank can have +ve and -ve pressure at certain times. Check valves in the system should prevent either condition getting excessive.

+ve pressure is controls by check valves in the fuel cap and one of the valves in the charcoal canister. -ve pressure is controlled by another valve in the charcoal cansiter.

If you are getting excessive pressure then you should get your charcoal canister checked.

[GreyBeard]

what's a / where's a 'charcoal canister'?

[sjrainsford]

The charcoal cannister is for the Evaporative Emissions Control System.

[GreyBeard]

thank you, so where is the EECS then?? near fuel tank, exhaust, throttle? on the shelf in the garage cos they forgot to refit it??

talking of which, my garage, after an oil and auto fluid change 'lost' the under-engine protection sheet (fibreboard i guess) and when i asked them to re-fit it, they claimed it was never there! so if you're thinking of using a garage in newbury for your vehicle repairs, PM me first to check that it's not the one i spent £4,000 with!