Author Topic: Fuel tank vent - petrol smell  (Read 229 times)

Jakob

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Fuel tank vent - petrol smell
« on: 25 May 2019, 04:51 PM »
When I originally bought our 450SEL it was on LPG. A few years ago I converted it back to petrol. Since then it's always had a bit of a petrol smell about it, but recently it's gotten quite bad.

I've checked all the fuel lines, pump, etc and there's no leaks. I'm pretty sure it's coming from the fuel tank vent that exits under the left-rear of the car (no emissions stuff on our car). Two questions:

1) can anyone think why it's so stinky?

2) the tank obviously needs to breath in as fuel is pumped to the engine. Would there be any issues with putting a one way valve of some kind on the end of the vent pipe so air can go in, but not come out?

daantjie

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Re: Fuel tank vent - petrol smell
« Reply #1 on: 25 May 2019, 10:01 PM »
Do you have the charcoal canister setup on the engine bay? The vapours are drawn via this canister and check valves into the inlet.
Daniel
1977 450 SEL 6.9 - Astralsilber

Jakob

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Re: Fuel tank vent - petrol smell
« Reply #2 on: 25 May 2019, 10:06 PM »
Cars in Australia didn't come with the charcoal canister setup. There's a line from the tank but it just vents to atmosphere under the rear left seat.

ptashek

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Re: Fuel tank vent - petrol smell
« Reply #3 on: 26 May 2019, 12:57 AM »
At the back of the tank, bottom left side under the rear parcel shelf  trunk-side are two pipes which feed through the chassis through a large foam seal. Have you checked these as well?

Is the breather blocked by any chance, and the tank is venting elsewhere as pressure builds up? Could be via the fuel level sender seal at the top.
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TJ 450

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Re: Fuel tank vent - petrol smell
« Reply #4 on: 26 May 2019, 07:17 AM »
It depends on the year, post ‘76, the K-Jet cars, are supposed to have a charcoal canister in the engine bay. Prior to this, or the D-Jet cars, they just vented as described.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

Jakob

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Re: Fuel tank vent - petrol smell
« Reply #5 on: 26 May 2019, 08:55 PM »
The vent isn't blocked. With the fuel filler cap off, I can blow through the line easily. With it on, the tank pressurises slightly when I blow through it and then vents back out when I stop (top tip, don't breath in immediately after doing this or you'll end up with a mouth full of fumes).

Jakob

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Re: Fuel tank vent - petrol smell
« Reply #6 on: 30 May 2019, 09:03 PM »
So I checked under the car after a drive today. It's dripping a small amount of fluid out of the vent - possibly petrol. So it seems like the fuel tank is pressurising and forcing petrol out the vent? Any ideas why?