I just had this happen twice this past week. My 70 El Camino SS 396 has a vented gas cap on it. I filled it up at the local gas station and came home and parked it on my lift. Raised up the elky and drove my 69 Dodge Charger under it. Came out the next day and my car cover on my 69 Charger was soaked in gas. It seemed that from the heat of the weather, the gas expanded and went out around the gas cap, down the filler neck, and dripped onto the frame and onto my charger. Fortunatly, the charger was ok with the exception of a stained car cover. Today, I was working on the elky and when I was done, raised it back up and drove the Charger under it again. After a couple hours, I went outside to close up the garage and smelled gas. I looked and now again I had gas running down the filler neck coming from the gas cap. This time, it ruined my white tail stripe decal and loosend the adhesive for the trunk weather strip since it ran down into the trunk channel. graemlins/angry.gif

This is a brand new GM vented gas cap and the previous one that was on there did the same thing. I doubt that it can be the gas cap as this only happens when the tank is between full and 3/4 of the way full and only happens on warm / hot days even with high humidity. Can anyone tell me what to do as I was ready to put a nice impression of my fist in the quarter panel of my elky. Help is desperatly needed with this problem as a friend of mine has the same problem when he parks on a hill after filling up his chevelle.

I also forgot to add, the gas is not in the filler neck at least that I can see with a flashlight when the cap was removed. The only thing I can think of which is forcing the gas up the filler neck and with the pressure, forcing the gas around the rubber gasket. Can anything be done to correct this problem??????? :confused:

did that car come originally with a vented cap or a non-vented gas cap?

The elky from what I have read originally came with a vented cap. The car is pretty much all factory original so I doubt that the gas cap was changed out before I did it. I would say maybe about 90% all factory original as the car has only 44,000 miles on it.

Anyone else have this problem? If so, how did you fix it???

I wonder if when you are filling it up it is getting an air bubble trapped in the tank and when you raise it up the fuel is sloshing aroung and it is burping back, I would try not filling it all the way up and see if it has this problem. Also does it have an overflow tube on the filler neck? Just a thought

Joe,

this is a 4 post lift that I have that you drive onto the ramps and just raise the whole car up. There is no real rocking or bumping of the car as it pretty much remain motionless. As for the fill tube, I dont think there is any overflow tube on it. There is only one filler neck tube that goes into the tank. I think if you overfilled it, it would probably just come out of the fill neck part. I am thinking about possibly drilling a very small hole into the gas cap so the tank would vent better. I wouldnt prefer to do this but I also dont want to keep ruining the finish on my Charger.

What would happen if I ended up drilling a small hole into the gas cap? Would that relieve the vapor pressure when the weather gets hot out? Wouldnt that also let moisture get in? :confused:

Do a search before you drill the cap, it seems I remember a member trying that and the problem changed, everytime the car moved forward gas sloshed and came out the hole he drilled.
I have a vented cap on my 70, but always wondered why pressure built up if the cap is supposed to be vented. It turned out the caps vent inward, they will let air in as the gas level drops but the check valve in the cap won't let pressure out. I tried 3 different new caps and they all did the same thing and built up pressure, but none ever leaked gas like yours. I think you need a new cap and I would also check the top of the filler neck to see if there is anything interfereing with the cap and filler neck making an air tight seal.

Wayner,

The neck of the gas tank is in excellent shape and is not out of round. When I take off the gas cap on a hot / humid day, the cap litterally blows out of my hand with the pressure that has built up in the tank. The problem is not with the car sloshing the gas around as it did not appear to leak when I brought it home from the gas station. The problem was when the car was sitting still and NOT moving on my 4 post lift. I checked the gas cap and it does allow air in but has resistance letting air out. It did let air out but at an extremely slow rate. ( I know, I probably should not have put my mouth on the gas cap but that was the only way to check to see if the valve inside the cap was working). I also have done a search with numerous combinations and have found no results of any difinitive answers. This is a concourse car and I really do not want to change any physical appearance aspect of the car. It is almost like the gas cap has too much resistance venting outward but has plenty of room to breathe inward. graemlins/clonk.gif

Brian,

Sounds like you need to try some different caps, but I also find myself asking why this thing is building up so much pressure. Literally blowing the cap off when you remove it? That's just not right.

How long are you driving it before parking on the lift and experiencing the problem? Are you saying that you bring it down, start it, drive it for a mile or two, fill it with gas, drive back a mile or two and put it back on the lift and it happens?

Dan

Dan,

This problem occured after the elky was sitting for a while on the bottom part of the lift and then I brought it for gas the next town over. Maybe a 10 minute drive or so. When I went to fill it up and took off the gas cap, there was probably about 1/8 of a tank of gas left as it took like 17 gals of gas. When I returned home from getting the gas, I swapped out the places with the elky and charger so now the Elky was up top and I could start wiping down the undercarriage for an up coming show. The elky sat undriven for about two days in cool weather (70s) untill we had a hot/humid day (of about mid 80s-90s). This is where the problem started with the vapor building up and the gas pushing out. I had a similar instance last year where not that much gas was dripping down the filler neck with hot weather. this was late in the season last year in which I found an NOS vented gas cap to replace the what I thought was faulty one. The old one as well as a Stant one from a local auto parts store did the same thing as it is doing now. I thought I had the problem solved with the NOS cap but I guess after I put it on last year, we didnt have any really hot or humid days. I dont know what to think anymore as this is really starting to get the better of me and I am ready to just drill a small hole into the cap. The only thought I had about when the gas cap got blown off of the filler neck when I removed it was that it was down to 1/8 of a tank of gas in which there could have been a lot of vapor build up there which all vented at once when I removed the gas cap. Other than that, I am at a loss for ideas and words..... graemlins/clonk.gif graemlins/angry.gif :confused:

Must be a frustrating problem Brian.

Let me make sure I understand. From your last post - the way I'm reading it, took the car out, drove 10 minutes, filled it up and took 10 minutes to drive it home. You put the car on the lift, where it remained for two or so days and the weather was cool. Then it got warm and humid again.

Question#1: did you drive the car the day it was hot/humid, then park it on the lift, and THEN it started spewing? Or did the car simply remain on the lift, undriven when it started spewing? Meaning, was it on the lift for the two cool days, and remained there without being driven when it became warm/humid?

Question#2: Does your 70 use a fuel return line from the pump?

Here's where I'm going. Needless to say, the gas is stored in underground tanks, where it remains at ground tempature - fairly cool. You then pump 17 gallons of cool gas into your tank. I just don't see how 17 gallons of cool gas can heat up enough during a 10 minute drive to cause enough expansion or fuel vapor to leak past the cap.

Although the weather got warmer and more humid, the car is indoors, the sun isn't beating down on it, the fuel isn't being heated beyond the ambient tempature of the garage. So I'm struggling to understand how, if the car had been sitting all that time without being driven, it spontainiously started leaking due to pressure build up.

Sorry, I think I'm missing a key peice of the puzzel!

Food for thought. I'm in the Washington DC area so we get to, um, "enjoy" the same kind of weather you've got there in Jersey. Hot and humid. My '66 Impala, with the tank and filler neck very low and more horizontal, sits for days/weeks in my garage - with full afternoon sun beating on the garage door, with a full tank of gas without ever leaking a drop. When my wife gets home and parks her car in the garage and closes the door, it gets even hotter in there. The Impala has a NON vented cap and uses a vent line that goes up into the trunk and loops back down. There's never a heavy gas smell in the garage while it's been sitting there.

Another question: what blend of gas are you using? Did you fill up at a station that you don't normally use?

Dan

Dan,

Yes you have the situation correct as you stated in your first paragraph.

Question 1 : The day it started spewing gas, I did not drive it. It had been sitting on the lift in the air for about two days or so. QUOTE-"Meaning, was it on the lift for the two cool days, and remained there without being driven when it became warm/humid?" This is absolutly correct.

Dan, the car sits indoors inside one of those CoverIt garages. It is not 100% water tight but does one hell of a job keeping the water and other elements out and keeping my cars dry. One thing I will say about the garage I have....if you have ever been inside a green house on a hot day, this is exactly what it feels like inside my garage. The heat inside it just gets very muggy and humid more than what the outside temp is. I guess this is because the light comes in through the cover even though it is tan and acts like a greenhouse effect. In the summer on a hot day it sucks to work in there even though I have the roll up door open, it still gets hot. A plus in the winter time though as it seems to retain the heat.

Question 2 : I guess it might be the above part about the greenhouse effect which could be causing my problems. Although, I would still think the vented gas cap would allow the vapors or pressure to escape and keep it at an equalized pressure. The last couple of days it has been fairly cool so I have had no problems with it.

The type of gas I run in all of my antiques is Sunoco Ultra 94 which I have been using ever since I have gotten all of my cars, so that has unchanged unless Sunoco added something new to the gas.

Today it was mid 80s or so with relatively no humidity and the gas cap was fine and had no pressure behind it when I opened it. I checked it before I pulled the elky out and let it sit idleing for a while to burn up some of the gas. When I pulled it back in, I again checked the gas cap and still no pressure behind it.

I graemlins/clonk.gif am graemlins/clonk.gif completely graemlins/clonk.gif baffled...... graemlins/clonk.gif graemlins/clonk.gif graemlins/clonk.gif

I agree the problem sounds like the gas cap I am not sure if they are like a Rad. cap that has diff. pressure ranges. But I am wondering if like it was said in an earlier post that you are expanding the fuel as you drive it back and, when you drive it up on the ramps it may lock some fuel in the neck due to the pressure build up and this may be causing fuel to push out. Did you have this problem when you have had it parked down low I just wonder if it is getting hotter sitting up top cause heat obviously rises I would check on the cap start with the easy fix. if you can't do any good with the cap maybe look at another vent solution GOOD LUCK smile.gif

When the elky is on the bottom spot (ground), I have not had any problem with gas spewing out. This could also be because it is cooler on the ground than up in the air closer to the point of the garage. Also, when the car has been on the ground, those days have not been as humid as what the day was when it spewed gas last.

Well Brian, given the fact that the thing spontainiously spews, which - incidently, reminds me of my youngest son when he was a baby, confirms that the fuel in the tank isn't being heated by the exhaust system nor by fuel being returned to the tank from the pump. There's not heat in the system other than ambient. Also confirms that pressure isn't building in the tank from returning fuel.

I'm still having trouble buying into the notion that air temp 7 or 8' high in your enclosure gets hot enough to cause this to happen. Think of all the folks that take these cars to shows, in the heat of the summer, with the sun beating down on them while parked on an asphalt parking lot. No spewing problems. It would be interesting to know what the temp is up there on a hot day. Got an out door thermometer you can stick to the side of the lift leg at the same height of the tank?

So, my guess at this point is the cap isn't allowing whatever pressure builds to escape (duh!) There's a handful of options as I see them.

1) Try some other caps. Obtain different brands, from different locations if possible. I understand the NOS thing but NOS isn't necessarily the best solution if the part has been sitting around for 30 years. I wouldn't run a NOS t-stat for instance.

2) Loosen the cap when you park the car on the lift. I think this is a viable option.

3) Leave the Elco down, put the Charger up. Would be interesting to see if the Charger did the same thing under the same circumstances.

Dan

When the car is on the lift is it level or tilted down on the filler side? A tilted car can cause the bottom of the fill tube to be below the gas line and prevent any trapped air from geting out when it expands. Seems like a full tank would not need much of an angle for gas to block the bottom of the tube.

Dan,

My elky has never spewed gas at any car show so why it is or was spewing gas out inside my garage on the lift. I checked the gas cap again today and no pressure was behind it still. I am totally confused.

I will certainly try that idea about using the outdoor thermostat and see what the temp variations are. I can almost guarantee there will be at least a variation of 5 degrees if not more inside on a hot day than the outside temp.

So far, I have tried 2 different gas caps from 2 different stores. One is an NOS one that is on there, one is a Stant (which I think made them for GM). I have even thought of just removing the gas cap all together though when it is on top but the thought of having my battery tender charger on at the same time and something sparking is just a bad idea.

The charger does not have the problem as there is a vent line that connects to the filler tube and goes down through the trunk floor.

Shooter...

The lift is set up so that when it is at rest on the safety's, the car is perfectly level. (at least it was when we set up the lift 3 yrs ago). I highly doubt the lift has settled crooked on the thick asphalt in that time as the lift still looks the same when the car sits on it.

Curious about your problem (related to my own on my '69 years ago), I did some research.
http://www.inlinetube.com/Gas%20Tanks/Chevy%20Car/CGM34K.htm
and
http://www.inlinetube.com/Gas%20Tanks/Chevy%20Car/CGM34J.htm
They obviously have two different tanks for different regions where the 1970 Clean Air Act applied, and not.
I notice you're in NJ, but the question is, is your Elky a California car? If so, the following definition applies for EEC (evaporative emissions control):
evaporative emission control system: (EVAP pr EEC) A system for reducing evaporative emissions by means of a sealed fuel tank, a vapour-liquid separator, a three-way valve, an activated carbon filter, and a network of interconnecting hoses. Also called "evaporation control system"
See here for details of the 1970 emissions changes
http://tranhaz-mat.sctc.edu/Emissions_Testing/vehicle_air_emissions.htm
You are suffering from probable expansion of the gasoline due to heating. All I could find was that recommended fill levels for warmer ambient temperatures is 95% of full, meaning leaving at least 1 gallon of empty space for liquid expansion. Some info I found specified 90% of full, meaning 2 gal of empty space! (for a 20 gal tank)
As I learned, in 1970 they significantly changed emissions rules, resulting in the installation of the charcoal canisters, and 'non-vented gas caps'.
If your car has had the charcoal canister removed (was probably damaged), and the vent tubes on the tank plugged, installing a vented cap is a problem. With no vent, your gas goes out the filler when full. My '69 was a California Chevelle, and had an air pump, and I seem to remember a canister in the engine comp. It had a vent tube that looped into the trunk, and vented into the frame. It always took a sealed cap, and it was a '69.
My bet is that you should be using a non-vented cap. Check your tank for vent tubes. If they're there, there might be a way to vent the tank and not leak gas w/o looking for original emissions equipment that probably doesn't exist. I have no idea what your vacuum lines are like on your Elky, but I seem to remember my original motor had a line going to a cannister that looked like a coffee can mounted on the driver side next to the radiator, with a line connected to the tank. When I overfilled mine, the gas would leak out the vent tube in the frame all over the ground, as my cannister lines were long ago plugged with varnish. I personnaly have never seen a restored Chevelle with all emissions equipment, but I'm sure they're there. I'm really surprised nobody else was able to cover the cannister issue. As NY/NJ had the same air quality problems as CA in 1970, even if your car isn't a CA car, I bet it originally had a cannister way back when.
Mine did in '69.

On that subject, a question for you racers: Is gasoline expansion the reason why safety rules specify a 'bladder type' fuel cell? I never saw that explained, but it makes perfect sense to me now.

JR

JR,

My gas cap is a vented cap. I do not have the carbon canister which is I think started in 1971 on all cars. My car is not a california car as it was sold in Florida. My gas tank only has 2 lines coming from it. One for the fuel supply and the other that comes from the fuel pump is the fuel return. There is no other vent tubes on this car as the cap is the only "vent" the system had.

Well, you've got me. I didn't even know before researching it that some Chevelle's/El Camino's had fuel return (or vapor) lines.

My instinct tells me that something isn't right on your tank, or that your Elky isn't level on the lift, and it 'burps' gas out the filler when the pressure builds when the tank is 'full'.

Let us know what corrected it.

JR

I let the car idle for a while outside one day to burn off some of the gas. I also took the gas cap off and drilled a 1/16" hole into the center of it to allow a little more venting out of the cap. This way, excessive pressure will not add up and cause any more problems.

just my 2 cents worth. Isn't there a vent line going to a charcoal canister? If that line is clogged or pinched it could be causing your problem.

JUST MY 2 CENTS AGAIN. I really don't think it's a good idea to drill a hole in the cap. All it would take is one person to walk by or linger around that area with a lit cigarette or some other ignition source to come in contact with those fumes and that would be it. There has got to be an explanation to the problem. I'm all for modifying cars, that's half the fun, but on fuel venting systems, I would be careful .

Roberts68,

The 1970 El Caminos did not have a carbon canister. There were two lines going from the tank up to the fuel pump. One being a supply line and the other being a return line. The gas cap itself was "vented" as it said on the cap so gas vapor would still escape whether or not a tiny hole was drilled in the gas cap or not. A guy who was at the Super Chevy show who was parked next to me also had the same problem since he bought the car in 1970. He showed me the trick to drilling the hole and not making it visible. Also, it is harder than you think to start a fire with fuel vapor. I am a volunteer fireman and there is a specific range where fuel vapor can ignite. You can literally throw a lit cigarette into a pool of gas without it catching fire most of the time. (Kids....don't try this at home). Hollywood has made it seem that the slightest little spark can make a whole car blow up which is the farthest from the truth possible. Anyway, I dont want to go into a lecture of Chemistry as this is not the Team Chemisty web board. :D Anyway, I do appreciate your concern but I highly doubt anything will happen. If it does, you will see a story posted on here. graemlins/thumbsup.gif

Brain, I have the same problem with presure building up in my 70.Tank will blow up like balloon and buckle trunk floor.The New fuel tank I installed does the same thing.I also drilled a hole in vent of cap.It fixed the problem,but created another.Gas fumes not only leaked out,but when I'd take off gas would come runing out. At $2.50 a gallon for Sunoco Ultra I put orginal cap back on and try to remember to relieve pressure build up when I park car.Some day I will figure it out????..........Jim

Jim,

I see you fill up with Sunoco Ultra also huh??? Thats all I put in my 3 antique cars. I have not had a problem with the tank distorting or the floor buckling. Guess I have been lucky. Is your car a 70 Elky also???

Heat rises and the full tank of gas expands when hot seing that you have the car raised up that will increase the heat in the fuel tank also the gas cap will take air in when the fuel cools and contracts . then when it gets hot it holds the pressure in causing your problem you need a a 2 way vented cap it sounds like you have a one way vented cap on it JMHO...Mike graemlins/thumbsup.gif

Hi, I'm new to the forum and have a similar, but worse problem with my 69 Elko. I'm pressurizing my tank while driving, at any fuel level. The longer I drive, the more it smells like a fuel bomb about ready to go off. After driving from California to Arkansas, my dog just refused to get back in it because of the fumes. No sign of it ever having a canister or return line. Problem didn't appear until I replaced the fuel pump with a Holley - could it be leaking back and causing the pressure? It has a vented cap, but I guess they only allow for combating vacuum? Any help would be appreciated as I really don't like the idea of a Viking funeral.

Terry

Terry,

What I did was drill a 1/16" hole in the gas cap. Yes, it lets out gas vapor, but it wont allow the tank to pressurize like you are saying. This seemed to correct my problem and the minimal amount of vapor that comes out of it now wont hurt anything unless you decide to stick a lit cigarette down into the filler neck.

Thanks Brian,

I'll drill the cap, but I'm still concerned about where all the pressure is coming from - just drove down my gravel road to get the mail - 3 mile round trip, less than half a tank of gas and had pressure built up when I got back.

Terry

Terry, how much pressure did you have build up? If it was a little, that is normal from the sloshing around of the fuel. It it was big enough to blow the cap out of your hand, you have other problems other than drilling a small hole in your cap. How are all of your fuel lines? Is that an original vented tank? Some things to consider.

Brian,

It builds up a LOT of pressure, will almost blow the cap out of my hand. Drove the truck for two years, stock,with no problems, then shoved in a GM high performance crate motor and a 700R4 - that's when I put the holley pump on it. other than that, the fuel system is the same as it always was - I think the pump is probably the culprit - when I drove it out from California, my son came with me, driving my vette - same basic drive train and gears - he got around 29 mpg and I got about 12 - and smelled like it was going to blow up all the way. I think it's just putting out too much pressure above idle and is somehow bleeding back to the tank.

Terry

Brian,

It builds up a LOT of pressure, will almost blow the cap out of my hand. Drove the truck for two years, stock,with no problems, then shoved in a GM high performance crate motor and a 700R4 - that's when I put the holley pump on it. other than that, the fuel system is the same as it always was - I think the pump is probably the culprit - when I drove it out from California, my son came with me, driving my vette - same basic drive train and gears - he got around 29 mpg and I got about 12 - and smelled like it was going to blow up all the way. I think it's just putting out too much pressure above idle and is somehow bleeding back to the tank.

Terry

Terry, on my SS396 motor fuel pump, I have a fuel line feed from the tank to the pump either a 3/8 or 5/16" line, a 1/4 return fuel line to the tank, and a steel line that goes from the pump up to the carb. Does your new holley fuel pump have only one inlet and one outlet? Maybe this is the problem as your excess pressure is being forced back through the feed line somehow and pressurizing your tank. just a thought!

Hi Brian,

No return line on it at all, think I'm going to pull that Holley pump off and put a stock unit on it - it's making the secondarys flood anyway, just too much pressure - but it's chrome and looks good in there - rats.

Terry

Chances are if your elky came with a return line, that would be your pressure relief. Might want to post a question in the fuel section to see if the 1969's had a return line or not.