Mate, there's petrol pouring out of your boot....
Discussion
I think that's what the guy in the Volvo shouted at me this evening while I was stuck in London traffic... Cue immediate pulling over into a side street, turning engine off and running round to the back of the car where I did indeed find petrol pouring back out of the fuel tank (which I had just filled up as normal) and dripping onto the hot exhaust!! 
After sending my girlfriend into a very conveniently located mini-supermarket to get anything to stem the flow (thank god they stocked kitchen towels!), we managed to start soaking the petrol up and a firm tighten on the filler cap stopped it pouring out. I nearly went nuts at some girl who walked passed, casually smoking a cigarette!
After 5 minutes trying to work out what to do, I decided to loosen the cap and see what happened. After an initial spurt of fuel down the side of the boot again, I was left with a filler nozzle full to the brim with petrol. I tightened the cap, got my girlfriend to start the car and after 2 mins of rough running the car settled down and seemed ok, so I loosened the cap (engine still running) and petrol started to fill back up into the filler nozzle again. I quickly tightened the cap, left it running 10 mins and then drove down a couple of sidestreets to make sure no more fuel was coming out which it wasn't. We then set off into traffic again with everything ok until 10 mins from home, the car stalled at a roundabout and every subsequent time we came to a halt (i.e. the engine wouldn't idle). Back home, a quick release of the fuel cap followed by a large whoosh as the pressure equalised restored normal running.
Has anyone else had the problem of petrol pouring back out of the tank, down the boot? The only thing I can think of is that there must have been an airlock in the tank when I filled up. The stop-start London traffic meant the exhausts heated up the petrol tank causing expansion that forced petrol back out of the filler nozzle. The rough running at the end of the journey presumably was caused by the cap being too tight, and there being too much of a vacuum in the petrol tank for the engine to draw fuel from at idle... Does this sound feasible?
Must admit I was a bit shaken afterwards when I saw the puddle of fuel that had dripped off the exhaust and onto the road!
After sending my girlfriend into a very conveniently located mini-supermarket to get anything to stem the flow (thank god they stocked kitchen towels!), we managed to start soaking the petrol up and a firm tighten on the filler cap stopped it pouring out. I nearly went nuts at some girl who walked passed, casually smoking a cigarette!
After 5 minutes trying to work out what to do, I decided to loosen the cap and see what happened. After an initial spurt of fuel down the side of the boot again, I was left with a filler nozzle full to the brim with petrol. I tightened the cap, got my girlfriend to start the car and after 2 mins of rough running the car settled down and seemed ok, so I loosened the cap (engine still running) and petrol started to fill back up into the filler nozzle again. I quickly tightened the cap, left it running 10 mins and then drove down a couple of sidestreets to make sure no more fuel was coming out which it wasn't. We then set off into traffic again with everything ok until 10 mins from home, the car stalled at a roundabout and every subsequent time we came to a halt (i.e. the engine wouldn't idle). Back home, a quick release of the fuel cap followed by a large whoosh as the pressure equalised restored normal running.
Has anyone else had the problem of petrol pouring back out of the tank, down the boot? The only thing I can think of is that there must have been an airlock in the tank when I filled up. The stop-start London traffic meant the exhausts heated up the petrol tank causing expansion that forced petrol back out of the filler nozzle. The rough running at the end of the journey presumably was caused by the cap being too tight, and there being too much of a vacuum in the petrol tank for the engine to draw fuel from at idle... Does this sound feasible?
Must admit I was a bit shaken afterwards when I saw the puddle of fuel that had dripped off the exhaust and onto the road!
rmaurer said:
The rough running at the end of the journey presumably was caused by the cap being too tight, and there being too much of a vacuum in the petrol tank for the engine to draw fuel from at idle... Does this sound feasible?
I don't think the cap can be too tight because the tank vents through a carbon filter. If you overfilled it is it possible that the pipe to the carbon filter filled up to and therefore couldn't vent? So when the cap was applied it created a vacuum because of the blocked vent pipe? Or something like that?
Had the same initial problem with the Tusc once last summer. Was out for a drive on a very hot day. Filled up the tank, pulled in a few miles later at our next pre-defined stop, and restarted when I came back and restarted it, found a whole heap of petrol pouring out of the back. Scratched my head for a couple of minutes then drove off. Never had a problem since (that was last June or so).
Fuel expands when it warms up, so filling to the brim with cold fuel could cause trouble if it heats up quicker than you are using it up?
The good news is that it is almost impossible to get petrol to light just by dripping it onto a hot exhaust, it needs a spark or flame to light it. (The flash point of petrol is above the boiling point, so it boils before it catches fire. Oil and hydraulic fluid on the other hand will spontaneously ignite if you get them hot enough.)
The good news is that it is almost impossible to get petrol to light just by dripping it onto a hot exhaust, it needs a spark or flame to light it. (The flash point of petrol is above the boiling point, so it boils before it catches fire. Oil and hydraulic fluid on the other hand will spontaneously ignite if you get them hot enough.)
GreenV8S said:
The good news is that it is almost impossible to get petrol to light just by dripping it onto a hot exhaust, it needs a spark or flame to light it.
Thanks, that's good to know!
UKBoB said:
In your opinion, after a fill to the brim (which is what I do every time) how much driving is necessary to bring the fuel level back down. 5 minutes worth at 2-3k revs?
I filled up to the first click of the pump, then put an extra 50p in (normally it takes £1-2 more after the first click) so I didn't think it was too full... I still soaked up 2 whole kitchen towel rolls worth though, and left probably 1/2 a pint on the road! Seemed like a lot when I was fighting to stem the flow! That was after 15 mins of idling since we'd left the petrol station...
UKBoB said:
In your opinion, after a fill to the brim (which is what I do every time) how much driving is necessary to bring the fuel level back down. 5 minutes worth at 2-3k revs?
I don't know, but you may be able to work it out if you can estimate how much it overflowed by. For example mine has a 45L tank so 5% (guessed) expansion would correspond to 2L ish, call it half a gallon, ten miles of normal driving or perhaps half an hour in a traffic jam.
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