Diesel fuel blowing back out of filler - anyone else had this? (1 Viewer)

Feb 11, 2017
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Last week I had something I've never experienced before. On going to fill up with diesel, I undid the filler cap and diesel gushed back out of the cap, soaking me! Obviously pretty unpleasant being covered in diesel, but I'm wondering if anyone else has had this problem?

It's a 2015 Ducato 3 litre engine, and was probably a quarter full at the time. It's fairly common to have a sort of vacuum when taking the cap off the filler but to be honest that has happened with all 3 of the Sevel vans we've owned. Obviously it was extremely cold at the time which may have played a part in this, but just wondering if anyone else has experienced it? A word of warning - try to stand well back when opening the diesel filler cap!!
 

pappajohn

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Not doubting you but...

It's NOT a sealed vessel.... If it was it would collapse as the pump draws fuel from it or the vacuum would prevent fuel being drawn.
Any pressure would be vented to air through the same breather system.
 
OP
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Feb 11, 2017
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Whatever the case is, it certainly caused a fair amount of smelly diesel fuel to squirt out! But I’m sure it’s not just me that has had the noise when opening the fuel filler, which may not be a full vacuum, but surely implies some sort of suction being broken?
 

mikebeaches

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Not had the blowback of diesel - thankfully. But certainly experienced the vaccum effect plenty of times when opening the filler cap on our X290 and previous X250.

About 45 years ago I had a petrol car breakdown on Spaghetti Junction M6, because the filler cap had become blocked and prevented fuel getting to engine. Took cap off, with difficulty, and huge whoosh as air entered. Engine started straightaway after that. Lesson learned.

So it must be a partial vaccum on the Sevel vans?
 

mike mcglynn

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I used to get a whoosh of air when taking off the fuel cap on my 2006 Ducato its something like negative pressure differential I think.

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Feb 16, 2013
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once had a bedford ha van , always seem to be running out of petrol but never showed empty and could never get much in, anyway on investigation what had happened , at some point the vent must have got blocked and the sides of the tank had been sucked together trapping the gauge and halving the capacity, new tank cured it and always been wary of blocked vents ever since.
 
Aug 6, 2013
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Modern vehicles cannot vent directly to atmosphere. There's normally a canister in the breather line to catch vapour that is purged at an appropriate time using engine vacuum and controlled by the ECU. The tank will have a slight depression when opened. I don't understand how a vessel with internal pressure below atmospheric can spew fuel - especially one that is only quarter full. Take a close look down the filler tube - there may be a small bore pipe in there that is the breather. Maybe the fuel trap in the breather line is malfunctioning.
 

TheBig1

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many many years! since I was a kid
i would say a faulty breather fuel trap too
 

TheBig1

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an inrush of air ejecting fuel trapped in the breather. I realise the op said they got soaked in diesel, but from experience a little goes a long way and stinks

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OP
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Feb 11, 2017
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an inrush of air ejecting fuel trapped in the breather. I realise the op said they got soaked in diesel, but from experience a little goes a long way and stinks
It certainly stank! Obviously I don’t know the exact volume, but it was enough to leave clothes (sweatshirt and trousers) distinctly damp.☹️

So why would fuel be trapped in the breather? It hasn’t done before, ever, and didn’t when I filled up again a few days later (standing well back, of course!). Could it be related to the cold?

And - it’s probably pretty clear by now I’m not at all technical - if as people have said the fuel tank system is not in any way sealed, how come I, and a number of other posters, have regularly had the sound of a seal breaking when undoing the filler cap?

I just really don’t want this to happen again...
 
Aug 6, 2013
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But that's going to cause excessive vacuum... Where has the pressure come from.
There's nothing to cause pressure in the tank except a blocked vent and heat.... And at this time of year that's doubtful.
Here's a picture of a tank breather & vent system (just to confuse :)):

Diagram-pic_0.jpg


1 Fuel tank cap, poss. with venting valve 2 Fuel tank 3 Fuel pump 4 Canister purge valve/regeneration valve 5 Intake manifold 6 Fuel tank pressure valve

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pappajohn

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Looks to me like that's venting the tank to the inlet manifold via 6, 7 and 4 rather than venting directly to atmosphere.
7 appears to be some kind of separation chamber to remove liquid from the fumes and 8 could be some kind of recirculating valve to send liquid back to the tank.
Still doesn't explain where the tank is getting its pressure from.
 

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