Yesterday while sat at the lights (in gear, clutch depressed, naughty), the engine had a little 'flutter', bit of wobble on the revs and a bit of engine noise, we'd just set off so the engine was cold. This afternoon we've just come back from a drive (to the local dealer to look at mark IVs ironically) and when I locked the car there was a whirring / grinding noise which upon closer inspection is coming from the fuel filler flap, and it is doing it whenever I lock the car. Finally, as I had the flap open I decided to open the filler cap (no idea why) and there was a release of gas from the fuel tank. The car has never done any of these three things in the past as far as I know. What is going on?

 

Mrs W wondered if someone has tried to siphon fuel off, but I'm on 425 miles for this tank of fuel so if they have they've not taken very much. Could the low fuel level also be something to do with it (currently showing range of 25 miles).

 

All very odd. Thanks

1 hour ago, GWoodhouse said:

Yesterday while sat at the lights (in gear, clutch depressed, naughty), the engine had a little 'flutter', bit of wobble on the revs and a bit of engine noise, we'd just set off so the engine was cold. This afternoon we've just come back from a drive (to the local dealer to look at mark IVs ironically) and when I locked the car there was a whirring / grinding noise which upon closer inspection is coming from the fuel filler flap, and it is doing it whenever I lock the car. Finally, as I had the flap open I decided to open the filler cap (no idea why) and there was a release of gas from the fuel tank. The car has never done any of these three things in the past as far as I know. What is going on?

 

Mrs W wondered if someone has tried to siphon fuel off, but I'm on 425 miles for this tank of fuel so if they have they've not taken very much. Could the low fuel level also be something to do with it (currently showing range of 25 miles).

 

All very odd. Thanks

The noise at the filler cap could / was most proably pressurised vacuum leaking slightly.  The fuel system is pressurised including the fuel tank to prevent escape of those hydrocarbons into atmosphere. After 5 years or so it is not totally unheard of to need to replace the fuel filler cap due to the o ring compressing or decomposing.

 

The release of pressure is nothing to worry about. As discussed above it is normal even if you haven't noticed before.

 

The flutter - who knows.  Monitor, see if it happens again. No Engine light I assume? You could get a scan if it really worries you. 

 

 

The noise from the filler flap will be the locking mechanism, probably obstructed by something and not able to complete its cycle.

 

I don't have on on the Yeti, my MKII Octavia had a solenoid, yours sounds like it is a motor.

45 minutes ago, TheClient said:

The fuel system is pressurised including the fuel tank to prevent escape of those hydrocarbons into atmosphere.

 

The release of pressure is nothing to worry about

That is a contradiction in terms, to prevent gases leaking or venting to atmosphere storage vessels, microbiology laboratories etc are maintained under a partial vacuum. You spoke of a "pressurised vacuum" so you seem to have covered all the bases!!!

 

That said the fuel tank may have a slight positive pressure if the engine is shut down and the fuel cap is removed quickly afterwards, that is because unscrewing it closes the valve to the expansion bottle of the  evaporative recovery system so that it can not fill with fuel if you overfill or do not put the pump nozzle all the way in, closing off that valve means any pressure in the tank will be released to atmosphere.

 

Edited 5 June, 20224 yr by J.R.

1 - Engine 'flutter' noise - Mine has done this, and usually when cold (and/or if idling slightly higher). I'm led to believe it can be auxiliary services starting up / using power from the engine (e.g., air con or heating), which dips slightly to accommodate the additional load and then re-balances the revs. So theoretically, totally normal 👍

 

2 - Fuel filler winding / whirring - The fuel cap has a locking mechanism inside which prevents opening when the car is locked. As with other areas of the car that can avoid getting planned preventative maintenance, the mechanism can lose its smoothness without lubricant.

 

3 - Pressure release - as the others have stated, this is also normal.

18 hours ago, J.R. said:

That is a contradiction in terms, to prevent gases leaking or venting to atmosphere storage vessels, microbiology laboratories etc are maintained under a partial vacuum. You spoke of a "pressurised vacuum" so you seem to have covered all the bases!!!

 

That said the fuel tank may have a slight positive pressure if the engine is shut down and the fuel cap is removed quickly afterwards, that is because unscrewing it closes the valve to the expansion bottle of the  evaporative recovery system so that it can not fill with fuel if you overfill or do not put the pump nozzle all the way in, closing off that valve means any pressure in the tank will be released to atmosphere.

 

Ha ha. That's a lot of text to argue with semantics without altering the conclusion.

 

Anyway, a vacuum is the result of negative pressure. But I fear we may be heading of course. Yours was the fuller answer though!! 

22 hours ago, GWoodhouse said:

Yesterday while sat at the lights (in gear, clutch depressed, naughty), the engine had a little 'flutter', bit of wobble on the revs and a bit of engine noise, we'd just set off so the engine was cold. This afternoon we've just come back from a drive (to the local dealer to look at mark IVs ironically) and when I locked the car there was a whirring / grinding noise which upon closer inspection is coming from the fuel filler flap, and it is doing it whenever I lock the car. Finally, as I had the flap open I decided to open the filler cap (no idea why) and there was a release of gas from the fuel tank. The car has never done any of these three things in the past as far as I know. What is going on?

 

Mrs W wondered if someone has tried to siphon fuel off, but I'm on 425 miles for this tank of fuel so if they have they've not taken very much. Could the low fuel level also be something to do with it (currently showing range of 25 miles).

 

All very odd. Thanks

I think there are two issues here.

No idea about the engine flutter, but as to the fuel filler cap noise, the locking mechanism on the fuel flap can fail. There's a thread on here about it somewhere.

It's a pain to fix IIRC, so if it is on the way out, some timely preventative action could save you a bit of bother.

Of course it might be something else, but it's worth knocking off the "could-be" list.

Edited 6 June, 20223 yr by EnterName