Topic: car gas caps

[2wheels]

Does anyone know.
How to test a car (honda civic) gas cap.
I know there is a pressure relief valve built into the cap. What pressure?
There is also a valve to allow vacuum to be built up in the tank, but does this also got a relief ?
Thanks

[mrbreeze]

The only way I know of would be to take it to a smog station. They have the machine to test if the cap holds pressure. I don't know about out of California but in this state the cap must function properly or else the vehicle will fail the smog test.

[DH]

Got an evap code? To answer your question, there's a purge valve, and a vent valve. It gets interesting and more complicated from there. IIRC, they can do a smoke check on the evap system, and it will reveal leaks in the system, including a cap. Just my .02, not knowing your exact issue.

[2wheels]

Engine light is on.  It is an evapluation code.  When I open the cap to refill sometimes I hear the hiss of air and othertimes no.  I don't need to fix it I am just curious and I cannot get a explanation of how the cap shoud work.  I have read and do mostly understand how the evap system works.  14 year old car, not worth the$ to get it repaired.

[cb650]

Well these bikes are 35 + years old so they not worth repairing?   If it just needs a new $10 cap wouldnt it be worth it?  Now it might not be worth a shop rebuilding the whole engine.  My understanding the emissions caps are supposed to keep vapors in but let air in as fuel burns off. 

[2wheels]

I understand keeping itgoing but with all the road salt few cars last 15years everything just rots.  So you have to be realistic when the end nears.  I did buy a walmart cap but the engine lights. Is still on and off.  The cap has 2 springs inside holding 2 rubber seals.  Ifit was just a total seal these would not be required so this iswhat left me wondering just what is thecaps job.