Fuel Leak - is this normal

Hi I am new to this forum and would ask for some advice. I have a 1989 2.5 TD 90 county, I get about 250 miles to a tank, approx 25 mpg, it has not spent much time off road. When I take the fuel cap off to fill up there is a big release of pressure, is this normal? I also have a large fual stain around the filler cap. I was getting much less mpg and noticed the breather pipe near the filler was not on properly, I adjusted this. I was wondering if the pressure was forcing fuel out of the filler cap and I could be getting better mpg. what is putting the fuel under so much pressure, unless this is normal.

thanks
Russell.

sounds like the tank breather is blocked, so while the diesel is being pulled out by the pump this causes a vacuum in the tank. hense the rush of air when you take off your cap. take the pipe off and give it a good clean, this should cure it.
better get it sorted soon or the next thing to go will be your pump.
as for the stain around ya filler cap. try and be a bit more acurate next time

Hi

thanks for the reply I will give it a try, do you mean the breather pipe that goes from the top of the tank to the side of the filler?

thanks
Russell.

yep, thats the one.