fuel tank pressurising


Hi I have just bought a 1989 (carb model)sportrak in great condition and am really pleased with it, however the fuel tank in pressurising in the warm weather which suggests the breather is blocked. I have traced the pipes from the tank and they dissapear into the body work, how do I get to the breather?

Nothing wrong.

Pressurising is normal. Also pressurised whilst driving.


I have had many cars do this not just a Daihatsu thing. I find it is more noticeable when you've driven a distance from a full tank and stop to refill. I was always under the inpression that all modern fuel systems are pressurised.


All daihatsu models pressurise their tank slightly, this is due to environmental regulations which limit the vehicles emissions from fuel or fuel vapours. They have a small plastic tube on the end of the breather pipe, this contains two opposing sprrings with a ball bearing between them. This sits in a rubber seal, as the tank uses fuel it creates a small vacuum, once it reaches around 3psi it forces the ball against the spring one way to admit air into the fuel tank. As the fuel expands from heat, the ball is forced the other way against the other spring to let pressure out.
If vehicles are used off road, or simply get older, the springs and ball corrode, it takes more pressure to move them either way. So if you have excessive pressure, remove the valve and clean with a good penetrating oil, and lubricate it with a few drops of engine oil annually.

If the pressure is not excessive, simply lubricate annually to prevent problems.

fuel tank pressure

Hi my 1998 Feroza has pressurised since it was new and it is normal. I only know when at a garage and you get that odd noise when removing the fuel cap. My Feroza was made for the middle eastern market and has an additional charcoal filter in the petrol system to absorb any evaporated fuel.


mick pretty