Fuel Tank Vent Needed?

[HawkRod]

I have a 1970 Road Runner with a FAST fuel injection system. I had a custom aluminum tank made with a fuel pump in it. My system runs at 43 PSI.

My tank came with a vent, and I ran a vent line to the top of the area where the axle sits. The problem I have is that the vent line spits fuel out of the tank when it is full and it builds up some pressure. I was considering redesigning my vent line to improve it, but then I thought:
Can I just block off the vent line and let my tank be pressurized?

Modern day cars have their tanks under pressure. Can anyone think of an issue with doing this?

As always, I appreciate the help and thoughts you might have...

Hawk

 

[5.7 hemi]

Don't do that! Get a vented gas cap instead. That will solve your problem.

 

[metaldad]

seems i have the same issue.
have had the cap semi tite, to allow pressure to escape
something else to buy.

 

[bigmanjbmopar]

You can use a non vented cap and drill two 1/8" holes on opposites sides being careful not to damage the gasket (I say this because sometimes it's hard to find a vented cap that fits), also the vent line needs to be extended the factory made a loop or forced pressurized fuel to have to travel uphill for a long distance with the theory that it would only make it so far in the line then drain back into the tank and used two lines one short one long for uphill and downhill venting.

Whatever you do DO NOT CAP A VENTED LINE! unless you like blowing up!


Another alternative is to get a charcoal canister and put the vent line to that, all of those have a another vent valve on them that will force open and vent outside after the fumes are filtered. This is the most modern method of venting, and will keep the smell out of your garage remember to make the lines loop and as long as possible.


Do you have a return line from the injection system back to the tank?

 

[HawkRod]

Don't do that! Get a vented gas cap instead. That will solve your problem.

Thanks - yes, I do have a vented cap (a 73-74 style gas cap), along with the vent at the top/front of the tank. This setup is what leaked.

You can use a non vented cap and drill two 1/8" holes on opposites sides being careful not to damage the gasket (I say this because sometimes it's hard to find a vented cap that fits), also the vent line needs to be extended the factory made a loop or forced pressurized fuel to have to travel uphill for a long distance with the theory that it would only make it so far in the line then drain back into the tank and used two lines one short one long for uphill and downhill venting.

Whatever you do DO NOT CAP A VENTED LINE! unless you like blowing up!


Another alternative is to get a charcoal canister and put the vent line to that, all of those have a another vent valve on them that will force open and vent outside after the fumes are filtered. This is the most modern method of venting, and will keep the smell out of your garage remember to make the lines loop and as long as possible.


Do you have a return line from the injection system back to the tank?

Thanks JB. So first, to answer your questions / suggestions: I have a vented 73/74 style cap on it now. I do also run a full return line with the Fuel Injection back to the tank. If I modify my vent line I was going to both lengthen the line as well as put a small surge tank into it where the vent enters at the bottom and exits at the top. This way, if some fuel is traveling up the line the air can "burp" itself past the fuel and exit, and the fuel can eventually drain back.


Can you help me understand why capping a vented line will make me blow up? My 70 is an original California car, and it used a non vented cap, a special tank and a sealed expansion tube that sat in the trunk. If my current system pressurizes due to lack of a vent, what will happen? The pressure could force fuel through the fuel lines, but my fuel line wants to be pressured at 43 PSI anyway. I guess the return could become a bit of a problem if it has too much pressure, but I can't imagine that the tank would have more that a few PSI of pressure.

Not disagreeing with you, just trying to learn and understand...

Thanks,

Hawk

 

[bigmanjbmopar]

Sure,

It's not so much your set up its today's fuel, unless your running 112 - 118 octane gas. 89-93 is going to have a good amount of ethanol in it which when hot expands and evaporates at a higher rate than the older gas. What used to be plenty of expansion space on the OE set up now becomes barely to not enough with today's gas.

I realize you're not really using any OE parts in your setup but the gas will still expand, so now you need more of a modern fix to a modern problem. I would say if you feel your tank is up to par with modern efi system then yes block off the vents and give a good run hot and full, bring it in shut it off and see if you any smell or gas is trying to bleed out anywhere. With the vents now do you lose any pressure? do you have a guage on the regulator? at 43 psi and vents it you may see a drop after you shut it off. I thought you were using your OE tank just modified, but you have a whole new custom tank? Baffles and all?

Where did you get the tank? Have you called them and ask them why they put vents on it? (IF IT'S CUSTOM) if you are trying to use a OE style tank then that's your problem.


READ THIS - Here is a great article to help you out about your problem, also you may want to call aeromotive for better advice than mine

http://www.hotrod.com/how-to/engine/1322-aeromotive-bolt-in-stealth-fuel-delivery-system/


"the Aeromotive fitting that is connected to the vent hose coming from the tank sending unit connection. The best way to install this vent is with a minimum 180-degree loop in the hose to prevent accidental siphoning from the tank through the vent hose."







some info on todays gas

http://www.eia.gov/tools/faqs/faq.cfm?id=27&t=10

( http://oilprice.com/Alternative-Energy/Biofuels/How-Much-is-Too-Much-Ethanol.html

"As it stands, the Renewable Fuel Standard (RFS) requires refiners to buy alternative fuels to meet a target of 18.15 gallons of renewable fuels blended with gasoline in 2014. The oil industry is hoping to see this lowered to 14.8 billion gallons." )


http://www.eia.gov/workingpapers/pdf/ethanol_blend_ratio.pdf



( Blow up, well how about imploade? lol

http://www.eia.gov/workingpapers/pdf/ethanol_blend_ratio.pdf )

 

[HawkRod]

JB,

Thanks for the additional information. I do have a custom built aluminum tank specifically built to have fuel pump built into the tank, and it has all baffles and high pressure fittings for AN fittings for all fuel lines.

Why does it have a vent? Great question that I cannot answer. I will digest the information and do a bit of research. Appreciate the help!

Hawk

 

[bigmanjbmopar]

No worries, I think worst case get the one way check valve fitting from aeromotive and at least you won't get the spill maybe just the smell which is better. Venting doesn't hurt and is a good safe way to prevent tank blow out issues. Call Aeromotive and ask for advice they sell other brand stealth tanks like gto etc they should be able to tell you what you need.

Just wanted to add, not that my car has EFI but my stock 69 RR setup would spill gas out of the vents on hot days when full. first thing is you find out that the replacement tanks these days flip the vent lines for some reason, then you learn todays gas expands faster than the old days so between fixing my flipped vent lines and venting my cap and adding a longer line with a filter to the short vent on my setup I was able to eliminate the spill over, occasionally on real hot triple digit days I get a little smell but nothing like it was.


Oops almost forgot here is another great site for tanks in your situation


http://www.tanksinc.com/index.cfm/page/ptype=results/category_id=146/mode=cat/cat146.htm

 

[383man]

When the manufactors went to non vented tanks they went to a pressure/vacum release cap because they sealed the system so no fuel vapors get into the air. They vent the tank fumes into a charcoal canister which will store them and then when the engine is running they purge the fumes from the charcoal canister into the eng as the eng will just burn the fumes in the cylinders when running. The cap will vent pressure and vacum at certain setting so you dont worry about it building to much pressure or building to much vacum on cooldown which can collaspe a tank. Many also used a vapor recovery tank where the fumes went into a small tank and any fuel that may get into will drain back into the tank. The first year Mopar sealed the fuel tank system which was around 1971 or 1972 they actually vented the fuel tank into the eng crankcase as you can tell when you have one of them because the breather cap on the pass side valve cover will have 3 nipples on it instead of the normal 2 as the third line comes from the gas tank. Then when the car starts the fumes in the crankcase get pulled and burnt in the eng through the PCV system. I thought about doing that on my 63 as it came with a vented cap and on real hot days I can smell gas fumes in the gargae. Ron

 

[mopar 3 B]

I want to read the post after the tank vent was removed and nonvented gas cap installed.
Which will the tank do first explode or collapse? My vote is for collapse. If the tank is going to build pressure it should vent past any pump installed, blow the carb needles form their seats and flood the engine. But this is an injected vechical which bypasses excess fuel back to the tank. Interesting

 

[HawkRod]

I want to read the post after the tank vent was removed and nonvented gas cap installed.
Which will the tank do first explode or collapse? My vote is for collapse. If the tank is going to build pressure it should vent past any pump installed, blow the carb needles form their seats and flood the engine. But this is an injected vechical which bypasses excess fuel back to the tank. Interesting

So the vent has not been removed - I am exploring options. As you say, a standard tank may have issues. But has anyone REALLY seen a tank explode or collapse? I buy fuel for my mower in a 5 gallon plastic tank. It absolutely shows evidence from expansion and contraction of fuel vapors. But modern day cars handle this all the time. What is different?

I think the big question comes down to the tank. I do NOT know for sure that my tank is built to handle the pressure changes, so it could get dents or have issues without the vent. I am currently exploring a better vent system. I'll post more on what I come up with after the holidays and I get some time to design it...

 

[Yatzee]

I also have a custom aluminum tank with a vent spigot on the left front top side of the tank. It was made 1/2 inch I.D. and slightly barbed. This is actually a fill vent to prevent the tank from burping when filling but also serves as a vent for expansion and vacuum created by the fuel in the tank as it is depleted or expands from heat. Teed into the fill vent is a 3/8 vent line that exits at the top of the rear wheel well and has a double check valve mounted on the end. It allows air into the tank under vacuum conditions and prevents spillage in the event of roll-over - their a must have. The fill vent goes back to the filler tube and attaches to 90 degree barb fitting I soldered onto the fill tube extension about 2 1/2 inches below the cap, on the side of the fill tube. Mine is side fill and when filling the air at the top of the tank exits right back into the fill tube. The vent mounted at the top of the inner rear wheel well keeps pressure and vacuum in the tank at zero and when parked in the garage there is absolutely no fuel odors present. You can get the check valves online at many places - their not cheap but really a must.

 

[bigmanjbmopar]

Modern day cars have vents and expansion tanks / canisters / backflow preventers to clean the vapor and recycle it back to the motor for clean burning, part of the smog stuff. Plus todays cars are made to run on todays gas with computer controlled systems to monitor everything. That's why I think if you apply some more modern day equipment to your setup it will work.

Example of backflow preventer you could get. http://aeromotiveinc.com/products-p...pecialty-adapters/one-way-check-valve-orb-06/


Also consider -

http://www.summitracing.com/parts/dsr-080401/overview/

http://www.summitracing.com/parts/tnk-vvr/overview/ (Probably the easiest solution for you right here for $15)

http://www.tanksinc.com/index.cfm/page/ptype=results/category_id=160/mode=cat/cat160.htm


Other Alternatives -

http://www.autozone.com/collision-body-parts-and-hardware/fuel-tank-vent-valve

So the vent has not been removed - I am exploring options. As you say, a standard tank may have issues. But has anyone REALLY seen a tank explode or collapse? I buy fuel for my mower in a 5 gallon plastic tank. It absolutely shows evidence from expansion and contraction of fuel vapors. But modern day cars handle this all the time. What is different?

I think the big question comes down to the tank. I do NOT know for sure that my tank is built to handle the pressure changes, so it could get dents or have issues without the vent. I am currently exploring a better vent system. I'll post more on what I come up with after the holidays and I get some time to design it...

 

[HawkRod]

I finally finished my fuel tank vent. I haven't filled up my tank and used my car much, so I can't yet tell you if this works or not. I will update this thread once I know how well it works.

So my idea was to use a radiator overflow tank. The one I bought is a stainless 2" round unit. It has two connections. The first connects directly to the bottom, so fluid laying in the bottom of the tank can run out of this connection. The second connection is a tube that goes through the bottom and the tube is open near the top of the tank. So fluid would need to be near the top of the tank before it would escape from the second connection. Here is a picture of the tank:


Since this tank will be on its side at an angle, I wanted the second connection to be as high up in the tank as possible. I bent a small piece of line to connect it with the internal tube. It would connect and sit approximately as I show here (obviously inside):


I'll update this thread again in a month or two once I filled the tank in warmer weather and see how well it works.

Hawk

I connected my fuel tank vent to the first connection (this is the lower line in the picture below). This means when air expands and pushes fuel into the vent line, it will all end up in this overflow tank. The air can pass out through connection two and out of the tank (This is the upper line in the picture below). The fuel can then run back down into the fuel tank.
The only way that fuel will end up on the street is if more fuel is pushed out than the overflow tank can hold. Then it will flow out connection two. I made a temporary bracket that bolts to existing bolt holes, so nothing was drilled or messed with from an originality perspective. If this solution works, I will come back later and make a nicer looking bracket. The whole assembly is out of the way of the axle as well.

It's hard to describe, but hopefully that description made some sense. Here is a picture of the setup under my car: