'79 Gas Cap & Fuel System Vacuum
Thread Starter
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
'79 Gas Cap & Fuel System Vacuum
After my '79 sits for a couple months it will suck air for a couple seconds as I open the gas cap. It's the original tank with internal bladder. The EVAP system has all new hoses, new charcoal in the canister and verified valve operation in the canister. Is this normal or is the gas cap failing to allow air to enter? It did the same BEFORE I replaced the EVAP system hoses where I found the short rubber hose leading from the hard line to the center of the canister nearly disintegrated. Could that line from the fuel tank to the canister be clogged?
I keep thinking I've replaced all of the rubber hoses in the car but I've yet to do the little short ones on top of the gas tank. When I looked at them about a year ago they were intact and seemed OK if old.
I keep thinking I've replaced all of the rubber hoses in the car but I've yet to do the little short ones on top of the gas tank. When I looked at them about a year ago they were intact and seemed OK if old.
Thread Starter
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
I feel no air moving outwards and no odor of gas. Whenever the car sits for a while I make certain the fuel tank is quite low and my first drive is to a filling station less than 1 mile away. When driving (and filling) more regularly it doesn't happen. To repeat this happened both before I replaced all of the EVAP system hoses and after.
Race Director
Joined: May 2006
Posts: 18,648
Likes: 2,557
Not sure what your full situation is, why a low tank, is it season related? I could see if the bladder contracts as the air in the tank loses volume due to a temperature drop the tank would draw air in when the cap is opened in warm weather
Le Mans Master
Joined: Oct 2002
Posts: 7,098
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From: Las Vegas - Just stop perpetuating myths please.
Most gas caps are 2 way relief valves I recall. At least in California they can test the gas cap at any smog station if your curious. But if your really worried then you need to get a '79 service manual and study your fuel and vent system.
Thread Starter
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
Because I seem to remember reading that a locking gas cap was standard in the '79 Corvette. I was working in my uncle's auto/speed store in that day (high school) when locking Stant caps were hot "premium" sellers and the only available locking caps. "Hurst" was just one of the non-Big Three names I recall used in OEMs of the day and I guess I just thought it came with the "special" gas cap.
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Thread Starter
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
Something tells me the replacement cap will solve the problem.
Again, this makes me feel stupid. Almost as stupid as when working in the aforementioned auto/speed shop as a kid when I regularly manned the phone, looked up parts and quoted prices from that five foot-wide set of catalogs. Some known joker called one day asking for "muffler bearings" and I took the bait to ask everyone there how to find them while saying something like, "It sounds really strange but this guy wants muffler bearings." to hear "Keep looking."
Again, this makes me feel stupid. Almost as stupid as when working in the aforementioned auto/speed shop as a kid when I regularly manned the phone, looked up parts and quoted prices from that five foot-wide set of catalogs. Some known joker called one day asking for "muffler bearings" and I took the bait to ask everyone there how to find them while saying something like, "It sounds really strange but this guy wants muffler bearings." to hear "Keep looking."