The other day I pushed my luck on running out of petrol and ended up pulling in to fill up with just "5 miles trip remaining". I managed to get 55 litres of 97 RON into a tank which is claimed to hold only 45 litres. I understand that there is a button inside the filler pipe that allows you to "overfill" the tank and perhaps I inadvertantly pressed it with the fuel nozzle? Any other possible explanations?

The other day I pushed my luck on running out of petrol and ended up pulling in to fill up with just "5 miles trip remaining". I managed to get 55 litres of 97 RON into a tank which is claimed to hold only 45 litres. I understand that there is a button inside the filler pipe that allows you to "overfill" the tank and perhaps I inadvertantly pressed it with the fuel nozzle? Any other possible explanations?

 

That is what you probably did, unlilkely that the pump was actually measuring inaccurately.

 

I have got over 50 litres in on several occasions, deliberately, by leaning on the expansion tank bridging valve  at the side of the filler.   I thought it holds about 6 litres so 55 litres is fillling  the main tank, expansion tank and quite a bit of the neck.

 

I have run the Fabia more than 12 miles past zero on the fuel computer, I have heard someone do more than 40 miles but that has got to be in to sucking some air territory and therefore cavitation  of the fuel pump and giving the fuel system a bad time has got to be happening.

 

I think 55 litres is just about possible.  On fillling up on one occasion, pushing the expansion tank valve down, probably got in around 12 galllons ie about 54 litres, drove from Worcester to Glasgow and back, 610 miles, and still have 15 miles left on the range computer, not bad for a 180 hp petrol engined car ie well over 50 mpg!  

Edited 14 November, 201411 yr by lol-lol

I normally fill up with 5 or 10 miles range left and vent the tank to get between 50 - 55 litres in.

The other day I pushed my luck on running out of petrol and ended up pulling in to fill up with just "5 miles trip remaining". I managed to get 55 litres of 97 RON into a tank which is claimed to hold only 45 litres. I understand that there is a button inside the filler pipe that allows you to "overfill" the tank and perhaps I inadvertantly pressed it with the fuel nozzle? Any other possible explanations?

Probably did as you said yes. I've done it before by accident.

Were you filling at a funny angle?

Take care, the tank is 45 litres or pretty near, 

you are 'venting' and brimming up the pipe & the expansion pipe.

 

Do not do that then Park Up, it is dangerous.

you have no expansion available which is rather important if the weather changes,

ie it gets hot / sunny.

 

The Venting is handy to extend the range before the next fill up when doing a journey.

 

george

 

PS

Not trying to start a debate again, but IMO (there are plenty of threads on Super Unleaded & Twinchargers.)

You might find it better to use 99 ron Minimum Tesco Momentum 99 or Shell V-Power Nitro 99 Minimum if available 

rather than the other UK Super Unleaded 97 Minimum from Sainsbury, Esso or BP.

The Recommended Fuel is 98 RON, 

but at least using the 97 is preferable to using 95 ron minimum Unleaded.

Edited 14 November, 201411 yr by goneoffSKi

Glad to hear that you aren't trying to revive one of your rants again George but your theory about 99 RON really is complete and utter nonsense. The VAG Twincharger engine is designed to run or 98 RON -or- 95 RON as required by some obscure EU QANGO.

 

The Fabia vRS quite satisfactorily achieves this magic by manipulating the engine timing using a knock sensor (delaying the ignition when using lower octane fuel and advancing it with higher octane fuel). There is an argument that says that 98 RON is optimal and you should always use that. However, 99 RON is no better or worse than 97 RON unless you are taking the car to a track day or thrasing it along some Autobahn.

 

Stick to 97 RON mate, it is widely available and is cheaper than 99 RON which is apparently only available from Shell garages or your local grocer

 

ps - I have no idea why you managed to overfill your tank by some 20%, you were probably ripped off!

Has your research not shown the issues some have had with Spark Plugs.

 

You have been reading about them for near a year.

 

?

Are you coming along to the vRS get together next May to see the cars in the flesh?

Its doubtful hes 'been ripped off' by getting that much fuel in.

Its much more likely hes accidentally vented the tank..

I put in 40.8 litres this afternoon with "Just 25 miles to go". Calculated MPG since previous fill-up was 48.

The same figures for the earlier fill-up were 54.65 litres and 34.6 MPG.

Overall (credible) MPG since I bought the car is 39.5 over about 8,000 miles.

The only logical conclusion is that I must inadvertantly have depressed the "overfill" button 430 miles ago.

I had a Monte Carlo a few years back.. And I went about 30 miles on zero.. Bear in mind some of that was going around a ton foolishly, but there was a reasonably good looking girl at the end of it, turned out the only company I got was the rac bloke who had to pick me up when it ran out.. I usually got 25 out of a 'zero' as I used to lose my wallet all the time.. But I've never got more than 42 into my vrs..

There is no 'expansion tank', but there is a certain volume of space in the tank that you can't fill without venting some air (and fuel vapours) out of it. This comes about naturally and deliberately as a result of the filler neck not meeting the tank at its highest point. What I don't understand, is why Skoda provide a means to accidentally or deliberately fill this expansion space? I'm pretty sure I searched the Mk1 owners manual for any mention of the 'button' without success. Do you guys get any info about it in your manuals?

 

If there's a safety, or environmental reason for not filling this expansion space, surely there should be guidance on how to use, or avoid using, the vent button? I know on the Mk1 forum, diesel users routinely use it, but petrol users are often warned off, and the only explanations I can remember seeing are that petrol expands more than diesel, and that overfilling a petrol car may bugger up the carbon canister.

 

Thoughts? Understanding?

There is no 'expansion tank', but there is a certain volume of space in the tank that you can't fill without venting some air (and fuel vapours) out of it. This comes about naturally and deliberately as a result of the filler neck not meeting the tank at its highest point. What I don't understand, is why Skoda provide a means to accidentally or deliberately fill this expansion space? I'm pretty sure I searched the Mk1 owners manual for any mention of the 'button' without success. Do you guys get any info about it in your manuals?   If there's a safety, or environmental reason for not filling this expansion space, surely there should be guidance on how to use, or avoid using, the vent button? I know on the Mk1 forum, diesel users routinely use it, but petrol users are often warned off, and the only explanations I can remember seeing are that petrol expands more than diesel, and that overfilling a petrol car may bugger up the carbon canister.  Thoughts? Understanding?

The is a seperate pipe to the filler pipe that runs parallel with the filler pipe bu tis effectively blanked off at the top bar a small pipe that runs to the vent button/valve.

 

When the fuel cap is on the valve is open alllowing air to travel along it. Or you can depress it when filling the tank and the fuel will fill that pipe too.

 

It is not the petrol expands more than diesel as it heats up but that the flash point, or the temperture that the fuel has significant evaporation is only 2 c with petrol.   So even with the temperature at only a few degrees the pressure above the fuel can rise.   Due to emission laws the cap should not vent fuel unless in extreme circumstance hence their circa 5 litre "plenum" chamber to cope with this.

 

As I have written on another thread, particularly with petrol, only fill the plenum pipe if you are gonig to use at least that much fuel ie about 60 miles immediately so the car is not parked and warming up and the fuel in the tank have insufficient space to evaporate and condensate in to.

Petrol emits vapours, diesel does not really at ambient temperature. If a petrol fuel tank is vented and then overpressured (e.g. due to an increase in fuel temp), petrol vapour will be going elsewhere. Smelly, potentially dangerous (vapours can e.g collect in a garage and explode next time you flip the light switch) and environmentally unfriendly. So while venting the fuel tank, even permanently (aka ventectomy) is more than welcome on diesels, it most definitely is not recommended for petrol engined cars. If you really must do it on a petrol, drive at least 50 miles right after filling up.

Ah, useful stuff, thanks. None of the pipes going to the fuel filler area look like they'd hold more than a litre though, other than the fuel filler pipe itself. Can anyone explain the funky shape of the one nearest the '6' in this diagram?

 

It hadn't occurred to me that the filler cap presses that button as it's screwed in   . Hence why it's not mentioned in any manuals; it's not intended as a user control, just as an automatic 'process' that happens during refuelling. Before unscrewing cap, vent open: after opening cap, vent closed; after replacing cap, vent open again.

 

Edit: Bit of an unfortunate design, in that it is so easy to press the button accidentally with the nozzle, especially if re-fuelling from the 'wrong' side.

After you have Brimmed the Tank on a vRS & can see the petrol, Venting it can get 7 Litres more in.

 

So covering 50 miles after Venting might not be enough miles covered.

Do not Vent a car unless you are on a Trip and using the Fuel.

Be sure you have not Vented the Tank & then park up a car.

Edited 29 November, 201411 yr by goneoffSKi

So does this not matter on a Diesel then? I have found this really useful recently, its allowing me to only fill up once a week which is great, saves a few trips to the fuel station!

 

I do park the car in the garage afterwards, not noticed any smells