Gush of air from fuel tank

[lemonade]

Hi,

The other day when I went to fill up my car as I opened the fuel cap a gush of air was released. Is this normal or should I be worried?

Cheers

 

[rodenal]

Wouldn't worry about it, particularly if you were very low on fuel

 

[The_One]

its normal

 

[Brookert]

I would have thought it would be a gush of air going in? To relieve the low pressure created by the missing volume of fuel?

 

[p_r_i_m_e]

its petrol vapour from an almost empty tank

 

[Mickie]

the tank is sealed, when the tank is run low and its hot outside the tank fills up with gas and an increase of pressure from petrol.

once you open the cap it obviously removed that pressure..

sorry for my poor explanation

 

[lemonade]

Nah it wasn't air going in, as soon as I twisted the cap it started releasing air, before I even touched the fuel pump. The fuel tank wasn't completely empty, it was at the last bar, so there was a bit left. I guess it could have been the heat as it was really hot that day.

 

[Matt82]

The Evap system should make a slight vacuum in the tank. None of my cars have made the gush sound tho with working Evap

 

[Stormster]

My Civic does it all the time, nothings gone wrong with it yet lol

 

[shauncr91]

My car does it every time I fill up.

 

[ganesh]

My car does it every time I fill up.

Same here.

 

[PiKe]

Nah it wasn't air going in, as soon as I twisted the cap it started releasing air, before I even touched the fuel pump. The fuel tank wasn't completely empty, it was at the last bar, so there was a bit left. I guess it could have been the heat as it was really hot that day.

I'd love to know how you can tell the difference between air going in or coming out by the noise it makes?

 

[Mickie]

it makes no sense for air to be sucked in, but if he has his hand close by he very likely could have felt the gas flow past his hand

 

[Shad]

Keep an eye on this. If there is a problem with the venting system for the tank then it could lead to an excessive pressure build up. I had this on the Caterham after the last rebuild; managed to get a kink in the vent hose so the tank couldn't breathe. The pressure was so high that the bottom of the tank bulged and split.

May not be so bad if your tank is a normal plastic one on a road car though! But keep an eye on it, a small whoosh on an empty tank is quite normal.

 

[Dogbreath]

Keep an eye on this. If there is a problem with the venting system for the tank then it could lead to an excessive pressure build up. I had this on the Caterham after the last rebuild; managed to get a kink in the vent hose so the tank couldn't breathe. The pressure was so high that the bottom of the tank bulged and split.

There is no vent hose on a modern production car. The fumes are vented to a charcoal canister, and this is purged by the engine under certain operating conditions. It's therefore quite normal to have some positive pressure within the fuel tank.

 

[Brookert]

it makes no sense for air to be sucked in, but if he has his hand close by he very likely could have felt the gas flow past his hand

why wouldn't it? If a volume of fuel in a sealed container is removed, and no air has replaced it, what would happen to the pressure of the tank?

 

[Vita]

My car does it. I always wondered why it said 'Open fuel cap slowly'.

 

[tigerstyle]

are you putting lemonade in your tank again lemonade?

 

[PikeyPriest]

why wouldn't it? If a volume of fuel in a sealed container is removed, and no air has replaced it, what would happen to the pressure of the tank?

Because there will be a way to let air in surely. Otherwise there is no way the fuel pump could function. Try pumping 50L of water out of a fixed airtight box and see how far you get before the tank collapses or you can't pump anymore.

 

[phil675]

She's a gusher!