CL500 Fuel Tank Pressure?

[Jumbojim]

Gentlemen

When I open the fuel filler cap I notice a rush of air into/outoff the tank, I cannot tell which, Is this right or have i got a problem in the making?

 

[Tinkerer]

Think that it should be a vented fuel cap and so this should not occur, pretty sure mine is checked on every MOT. Other than that I'm afraid I cannot help.

 

[grumpyoldgit]

Some fuel tanks are slightly pressurised. Not sure on the CL's.
I did read an article about a guy who drilled a small hole in his fuel cap because he thought it should be vented and then had to go and buy a new one when he had problems with the car not running properly.
If no one gives you a definite answer, check with a MB dealer first.

 

[Jumbojim]

Mr Oliver from Prestige Cars can you answer this please?

 

[hotrodder]

Fuel tanks haven't had a 'simple' open vent for years due to evaporative emissions. Don't know the exact detail for a CL but pretty much everything involves an active vent(s) where fumes are stored in a charcoal canister* to be fed to the engine. This means it's usual for the tank to be subjected to a small pressure or vacuum

If the rush of air is small enough that you can't tell if it's pressure or vacuum in the tank it sounds normal to me. If something is wrong with the venting system resulting in excessive pressure differential i would have thought it'd be more obvious... kinda like the difference between opening a half full bottle of semi flat soda versus a half full fresh bottle that's been shaken if that makes sense

* these are a service item that's often missed (long interval/not something obvious etc)

 

[kth286]

Fuel tanks haven't had a 'simple' open vent for years due to evaporative emissions. Don't know the exact detail for a CL but pretty much everything involves an active vent(s) where fumes are stored in a charcoal canister* to be fed to the engine. This means it's usual for the tank to be subjected to a small pressure or vacuum

If the rush of air is small enough that you can't tell if it's pressure or vacuum in the tank it sounds normal to me. If something is wrong with the venting system resulting in excessive pressure differential i would have thought it'd be more obvious... kinda like the difference between opening a half full bottle of semi flat soda versus a half full fresh bottle that's been shaken if that makes sense

* these are a service item that's often missed (long interval/not something obvious etc)

Agree with that - it's normal for the whoosh.