2.0 petrol locking fuel cap.

[olebrock]

I have just bought from the 'shop' a replacement Bongo locking petrol cap and notice there is no depressurizing hissing sound when stopping the engine and undoing the locking cap which was very evident with the original Mazda cap.
Is or could this be a possible problem for the petrol injection system. ie no/low pressurized petrol tank?
I have had this fitted for a couple of weeks and only noticed the difference when stopping to re-fuel, I havn't noticed any difference in performance but would like the experts' opinion.
Many thanks,

[apole]

Hi,

I didn't think the tank on a bongo was pressurised at all. I just thought it was drawn from (and excess returned to by the pump) at normal pressure.

The vent in the cap is to allow air to get in when fuel is drawn. The hissing you heard before was probably due to a blocked vent in the old cap causing a slight vacuum.

Could be wrong of course but that is what I thought.

Andy

[olebrock]

Hi Andy, you could be right, but I get a strong wiff of petrol fumes when opening the Mazda cap (air/fumes coming out), with the replacement locking cap there is no hissing or strong wiff. If air was going in as you suggest I would not get the strong petrol smell ?
The Mazda cap has a solid o-ring at the base of the thread but the new locking cap has a 'c' cross-section shape seal, wondering if this is not sealing correct ?
regards,

[missfixit70]

Why do you want a seal? Either vacuum or pressure in the tank is a bad thing IMO.

[stringman]

You certainly should not have any pressure in the fuel tank. As mentioned above, the hissing will be caused by the vacuum in the tank which has been created by the fuel being used up being released. If you get a smell of petrol I would suggest that this is caused by petrol fumes being displaced by the in rush of air.

The fuel filler cap will be designed to breath to prevent a vacuum being caused so I agree that your old fuel cap probably had the breather blocked

[Bob]

Yep, I recon you've fixed a small problem you didn't know you had, before it caused a breakdown.

Well done.

[olebrock]

Mny thks for your replies, I know that some fuel injection systems (common rail ?) use a small pressure in the fuel tank and I just wanted to be sure this was not the case with Bongo. All running well now