p38 v8 fuel tank breather?

dove · Feb 10, 2011

everytime i fill up with petrol (very often)when i remove the cap there is a hissing noise ,is this normal?.dont know if its pressure or vacum.anyone else get this?where would the breather be located,on the actual cap?the hissing lasts for 2-3 seconds,it runs fine doesnt seem to be starving of fuel.thanks

wammers · Feb 11, 2011

dove said:
everytime i fill up with petrol (very often)when i remove the cap there is a hissing noise ,is this normal?.dont know if its pressure or vacum.anyone else get this?where would the breather be located,on the actual cap?the hissing lasts for 2-3 seconds,it runs fine doesnt seem to be starving of fuel.thanks

Don't know if it's normal to be honest. Don't have a V8. Maybe it is as there is a tank pressure sensor involved. The V8 does have a very complex evaporation control system. Read about it in RAVE, if you can understand it your a better man than i am Gungadin.

Lone_Wolf · Feb 11, 2011

My 4.6 V8 does the same.

hoarec · Feb 11, 2011

So does mine......

j the range · Feb 11, 2011

mine to its just normal..

alfaitalia · Feb 11, 2011

I think its happened on every fuel injected car I have had inc my current one. The lower the fuel level the more the hiss, probably because there is more space for fuel to be vapour (ie expanded) then when nearly full. Well it makes sense to me!

dove · Feb 11, 2011

thanks guys,sounds like it is a normal thing for them do will read rave and see what it says.

Ridesafe · Feb 11, 2011

Perfectly normal; the lower the fuel level, the longer the hiss. As fuel level lowers with use the "space" (vacuum) is filled with petrol vapour, the hiss is vapour escaping.

Catty1952 · Feb 13, 2011

Mine does the same too

al-one-arm · Feb 13, 2011

mine tells you about the hissing on the fuel cap?

muddylane · Nov 25, 2011

Hi Everybody
I was going to ask the same question, but i think you have all provided the answer, i have the same on my 4.6 hse,

Brian

jt_armstrong · Nov 25, 2011

The wife's '99 4.6 hisses like a cat but my '97 doesn't make a sound. If the hissing is normal what's wrong with mine?

busa1300 · Feb 20, 2016

Mine hisses?? '98 HSE

oakey · Feb 20, 2016

Mine hisses especially after a long run but I thought it was sucking in to prevent vapour escaping and thereby saving the environment

MrGorsky · Feb 21, 2016

It's escaping pressure and perfectly normal.

The EVAP thing allows pressure to rise in the tank (with fluctuating ambient temperatures) to 5 - 7 kpa, and then if it rises above that a valve opens and any petrol vapour is sent down a tube to the charcoal cannister (thing by the EAS) where it is sent into the engine next time it's started.

Once you screw the filler cap down, it's a closed system so there could always be up to 7 kpa waiting to escape when you open the filler next time.

Ullapool · Feb 21, 2016

It happens with my 2.5TD as well.

wammers · Feb 21, 2016

RAVE SAYS.

Fuel filler cap
The fuel filler cap is designed to allow the fuel
tank to vent during the first half turn. When
removing, carefully loosen the cap one half
turn until resistance is felt, then pause to
enable fuel tank pressure to be released. Once
the pressure is released (hissing has
stopped), it is safe to fully remove the cap.
When replacing, tighten the cap clockwise
until you hear the fuel cap ratchet at least
three times.

busa1300 · Feb 21, 2016

Cheers

Thought it was a blocked breather and the pump was trying to suck the fuel tank inside out. I've seen it happen on GTE Astra

lazbaz · May 22, 2021

wammers said:
RAVE SAYS.

Fuel filler cap
The fuel filler cap is designed to allow the fuel
tank to vent during the first half turn. When
removing, carefully loosen the cap one half
turn until resistance is felt, then pause to
enable fuel tank pressure to be released. Once
the pressure is released (hissing has
stopped), it is safe to fully remove the cap.
When replacing, tighten the cap clockwise
until you hear the fuel cap ratchet at least
three times.

Does this mean the tank is designed to withstand pressure and vaccum?
I would have thought there would be a vent/release or intake system so when the fuel level goes down it lets air in and should it become pressurised by fuel vapour (hot day) it would release it.
any comments by anyone?
Regards

p38 v8 fuel tank breather?

dove

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wammers

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Lone_Wolf

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hoarec

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j the range

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alfaitalia

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dove

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Ridesafe

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Catty1952

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al-one-arm

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muddylane

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jt_armstrong

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busa1300

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oakey

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MrGorsky

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Ullapool

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wammers

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busa1300

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lazbaz

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