Petrol tank contract/expand noise

[ibizarich]

At least I think it's the petrol tank. Especially in the warm weather, but in the cold too as the car gets warm, I will periodically hear a fairly loud noise, the kind of sound you hear if you flex metal. I'm assuming its the petrol tank, but I'm not sure. It's always done it, and I just wondered if anyone else experiences this, or if it even is the petrol tank?

[b2tus]

My Tuscan does exactly the same thing in this hot weather. Reckon it can only be the petrol tank.
One hell of a woosh when I release the filler cap.

[chris watton]

Yes, it probably is the petrol tank...... when I filled the tank up, a few Saturdays ago, after I got stuck on the M40 for almost three hours in the blistering heat, taking the fuel cap off was a nightmare! The pressure from the fuel tank was enormous, taking over 5 minutes for the pressure to escape before taking the cap fully off - thought it was gonna blow up at one point, as the noise from the escaping pressure and tank flexing back to normal was so loud!

Edited by chris watton on Tuesday 18th July 18:08

[sideways mostly]

Err don't take this the wrong way chaps but is it sucking or blowing? ( Ooh er missus).I had a blocked breather pipe that led to the fuel pump inverting a large part of the petrol tank (in a Tuscan that is not a 350 ) I thought it was expansion due to heat but nope-I needed a new tank to replace the 2D one the pump had made. One hell of a pump on the Tuscan!
Thing is,when I tried to take the petrol cap off it gripped like a bar steward and hissed like mad when I managed to open it. No-one would believe me at the time-everyone thought it was positive pressure not negative. Just a thought just in case.

[steve11]

I always thought this had something to do with the exhaust system getting hot.