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Old 22nd May 2016, 22:32   #1
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Default Pressurized hissing sound when opening the fuel tank?

So my Bro in law just bought a 2nd hand City ZX because he is a learner. He came over to pick me up today for the first time so I decided to add some System G to his car since its a 2007 model. When I unscrewed the fuel cap, there was a hiss and quite a bit of pressurized petrol fumes came out, I mean I could see the vapour haze and it lasted for around 5 seconds continuously.

The car is parked in the hot sun all day at home as well as in office parking.

Is this cause for any alarm or is it just due to the heat ? Does it indicate a blockage somewhere in the fuel inlet ? Is it a known/common problem with the City ZX ?

Help would be appreciated. Thanks
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Old 23rd May 2016, 01:47   #2
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Post re: Pressurized hissing sound when opening the fuel tank?

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Originally Posted by Mortis View Post
When I unscrewed the fuel cap, there was a hiss and quite a bit of pressurized petrol fumes came out, I mean I could see the vapour haze and it lasted for around 5 seconds continuously.
Evaporated fuel vapors are handled by the EVAP system in modern cars where the fuel vapors are stored in a canister & then burnt off in the engine.
Check the picture in this post (Alto K10 AMT problem: Gearbox moving to 'N' unexpectedly) for how the canister typically looks like.
Quote:
Originally Posted by Mortis View Post
The car is parked in the hot sun all day at home as well as in office parking.
Very hot ambient temperatures will lead to accelerated fuel evaporation, however, it wouldn't hurt to have the EVAP system checked for any kinks or other blockages.
You could also have the ECU checked for any error codes related to the EVAP purge valve.
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Old 23rd May 2016, 10:09   #3
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Default re: Pressurized hissing sound when opening the fuel tank?

Quote:
Originally Posted by Mortis View Post
So my Bro in law just bought a 2nd hand City ZX because he is a learner. He came over to pick me up today for the first time so I decided to add some System G to his car since its a 2007 model. When I unscrewed the fuel cap, there was a hiss and quite a bit of pressurized petrol fumes came out, I mean I could see the vapour haze and it lasted for around 5 seconds continuously.
I own a '07 City Zx and have heard the hiss only when I refuel after a long time (like 1 month) but have never noticed any fumes, the same hiss is present even in my '12 City iVtec, so I do not think it is a matter of concern, my cars are also parked under the open sun. The hiss which I am talking about, lasts for approx half a second max.

You mentioned that the car was bought second hand, it is possible that even the previous owner/car dealer must have added some additives, that may be the cause of those extra fumes and hiss. IIRC my SA had clearly told me that Honda does not recommend any fuel additives/cleaners so please ask them before using System G, my car has clocked over 90000 kms without using any such additives and I still enjoy that free revving Vtec engine. Actually my SA even asked me not to fill up BP's Speed etc in any of my cars, as those fuels have got additives which choke the throttle body.
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Old 23rd May 2016, 10:34   #4
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Default re: Pressurized hissing sound when opening the fuel tank?

Hi Mortis, This is normal when the car is parked in the sun. Nothing to worry about.
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Old 23rd May 2016, 10:59   #5
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Default re: Pressurized hissing sound when opening the fuel tank?

The hiss is a normal phenomenon, ideally keep the tanks at more than 1/2 full to keep the fume formation and vapor loss at check. Hiss means your fuel tank vapor system is working properly and not releasing harmful fumes out.
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Old 23rd May 2016, 14:23   #6
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Default re: Pressurized hissing sound when opening the fuel tank?

Thanks a lot. Just wanted to clarify as the quanity and pressure of the fumes seemed to be quite a bit, A lot of vapour had built up in there and I havent experienced such a phenomenon in any of my cars before so I thought its better to clarify
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Old 28th October 2017, 15:48   #7
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Default Pressurised air coming out of fuel tank?

My Jazz X model has been giving a fabulous service over the past 6 years and has run slightly under 50 k kms. While I will be giving a 6 year ownership review in about 2 weeks, I have a question.

On the 27th October, the car was running low on gas and went to a gas station to fill her up. When the attendant, opened the cap, there was "husssh" noise with the air from Petrol tank going out and with some pressure. The sound was kind of muted and I was surprised, because it is the 1st time that this has happened. The attendant told me, "Sir, once in a while open the tank and then close it".

But am still surprised as to why it happened. Any thoughts ?
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Old 28th October 2017, 16:38   #8
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Default re: Pressurised air coming out of fuel tank?

Quote:
Originally Posted by aaren View Post
...there was "husssh" noise with the air from Petrol tank going out and with some pressure. The sound was kind of muted and I was surprised, because it is the 1st time that this has happened. The attendant told me, "Sir, once in a while open the tank and then close it".

But am still surprised as to why it happened. Any thoughts ?
Not to worry. When the petrol in the tank is sucked by the engine, air replaces it. Sometimes there is a delay, and there is a small vacuum and hence a negative pressure. Also, the volume of air inside the tank will change when hot and cold, and so the pressure. What you heard was just the tank equalising the pressure with the atmosphere.

This happens especially after a long drive, and the tank is almost empty.
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Old 28th October 2017, 18:08   #9
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Default re: Pressurised air coming out of fuel tank?

It's a common occurrence caused by pressure difference inside and outside the tank. Nothing to worry about. It happens with just about all cars.
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Old 28th October 2017, 18:20   #10
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Default re: Pressurised air coming out of fuel tank?

Mod note. Thread moved to 'Technical Stuff' section.
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Old 30th October 2017, 13:21   #11
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Default Re: Pressurised air coming out of fuel tank?

Please check your charcoal canister vent valve. It may stuck close. Also do you experience any problem while filling like filling nozzle get shut off early.
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Old 30th October 2017, 13:36   #12
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Default Re: Pressurised air coming out of fuel tank?

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Originally Posted by dracul View Post
Please check your charcoal canister vent valve. It may stuck close. Also do you experience any problem while filling like filling nozzle get shut off early.
Here is a useful video related to the subject

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Old 31st October 2017, 14:49   #13
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Default Re: Pressurised air coming out of fuel tank?

Quote:
Originally Posted by aaren View Post
there was "husssh" noise with the air from Petrol tank going out and with some pressure.
Are you sure it was air going out of the tank, rather than air coming in?
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