I have a ‘99 456M (Built 5/98, Assembly No: 30091, Engine: 50367) I know know they had several rehashes of the fuel system (mainly fuel cooling) but I was wondering if the gas cap is supposed to be a vented or non-vented cap? I hear a hiss on opening so makes me wonder if I have the wrong cap or my vented cap is all plugged up.
No expert on 456's, but just in general, your fuel system is usually a pretty sealed affair. The motor draws fumes out of the fuel tank through an EVAP charcoal canister, so the gas tank is generally under some level of vacuum. The EPA is not with venting gas fumes directly out to the atmosphere, so your gas cap should not be venting fumes out. It may allow some air in however, since the EVAP system pulls a vacuum and would otherwise tend to wanna crush the fuel tank. The hiss on opening the fuel cap is pretty normal for most cars. Ray
Thank you! I never heard the hiss with my 575 which is what prompted my curiosity. i thought 90s era Ferrari oil cap and fuel caps were interchangeable (in terms of size/thread), but oil caps were sealed/non-vented but fuel caps had little holes in the Ferrari black script lettering for venting… hence my confusion.
My 612 does not hiss when I remove the fuel cap, and the cap does not appear to be vented. The cap is metal and looks just like the oil cap. I have no idea if they are interchangeable.
You're right that if a car has a charcoal canister it will have/need a sealed fuel cap, but your 400i didn't have sealed fuel cap originally nor a charcoal canister (it must have been "emissionized" at some point in its life).
Typed too quickly so need to correct myself: 400 had an "open to atmosphere" fuel system and no charcoal canister -- 400i has the charcoal canister.
Ok update and actual answer. Gas caps are not closed (solid/no flow of gas, think oil cap) or vented (aka free flow of gas in / out ), but gas caps are breather caps (aka air can come in but nothing goes out). You should not put a solid (aka no breather holes) cap on a 2000s era Ferrari without risk. The breather holes are in the Ferrari script (I had to use my phone flashlight to get a good look, its hard to photograph well)
I lost my OEM gas cap right before my CARB inspection and wanted to take zero chances so I found and obtained the correct PN for my late 2003 assembly at considerable expense and yes there are a few different PN’s and configurations over the vehicles life. Different prices too. Very frustrating and I do not know exactly why they are different but these cars were constantly in motion as far as changes went. The released for my 2003M 456 was the same as the last 575M PN. I found the PN cheaper by purchasing an assembly for sale on ebay that just happened to still have the gas cap on it
The tank is always at atmospheric pressure. If you hear a hiss when opening the cap, this means that your evap system has a malfunction (usually the canister is clogged). Cap sealed on 456.
