Petrol Incident 2

[arcturus]

This is getting embarrasing and I need some help before I blow up a forecourt!! This problem started intermittantly at the end of last summer, disappeared over the winter (in spite of using the car all winter), but has now come back with a vengence.

Having filled up with petrol, when I start the engine, petrol comes pouring out of the filler cap and out of what I presume are the tank vents on each side of the car.

This continues for about 10 seconds after engine start and annoys both the forecourt staff and me who has just paid for the wretched stuff. This will then continue to happen every time I start the engine, until I have burnt off about 10 litres.

I don't want to be stuck putting only 30 litres in at a time 'cos I use the car most days and I would be forever going to the petrol station.

Any clues as to what I should be looking for when I get under the car this weekend.

1986 350i by the way.

Thanks in advance.

Sniffer

[mrcrappy]

mine holds about 35 litres, neither tank is blocked ( replaced all pipes and checked holes etc) both tanks are filling properly, if i take the breather off in the nearside rear wheel arch fuel pours out when i fill it up (the breather has a cap on it). if i fill up with more than about 15 quid and park with the nearside wheels up a curb or on an incline fuel pours out of the overflow ( top of filler cap) and also in hot weather the fuel seems to expand and go to the top of the filler tube, if i take the cap off it depressurises and goes back into the tank. its got me puzzled too and does my head in filling up loads on long journeys. good luck and let us know how you get on .
cheers jon.

[GreenV8S]

Don't know much about your setup but I think you have twin tanks with a balance pipe between them? Presumably you have a feed to the engine and a return from the pressure regulator. This is just a guess, but if the feed and return were not to the same tank, then in effect the fuel pump is transferring fuel from one tank to the other, and hopefully the fuel is returning via the balance pipe. The amount flowed by the balance pipe would depend on the level difference between the two tanks, and it might need a few inches of difference before it flows enough to keep up with the fuel pump. But if both tanks are fairly full, the 'high' one might overflow before this happens. All of this is pure guesswork but it might pay to follow the pipes and see where the feed and return come from. If they come from different tanks, I would say that is your problem.

[arcturus]

Thanks for the input. I am hoping to have a good go at sorting it tomorrow (Sunday). I have also noticed that the amount of fuel spat out increases with the ambient temperature.

Incidentally, I was under the impression that fuel capacity was in the region of 12 gallons/55 litres. I only ever get 40 in from when the fuel guage is below empty.

Will report back when I have news.