Small rubber fuel line leak at the frame rail.

[Fuggers]

Here's a scary story. I take my 72 c20 for what will be it's last fuel fill-up before winter. The tank had maybe 1/4 left and still filled another 20 or so gallons, I think (I checked my receipt later and the total bill was 70 bucks). I didn't hear or smell anything unusual so I hopped back in and fired it up, drove a couple miles to get lunch. When I stop and get out I noticed a trail of fluid going right into where I backed the truck up to the curb.

I pause for a moment then take a peak under the truck to see fluid really pouring out. I first assumed it was coolant because I had just topped it off and don't have an overflow tank yet, it was kind of a hot day. I then realized it's way too far back to be coolant . It was shooting all over the ground about a foot back from the cab on the passenger side. I quickly take a peak under there and notice fuel spraying out from the upper rubber line that connects the two hard lines right at the frame. It was literally spraying from 12 different pin holes and gushing from 2 larger ones, directly onto my resonator on the exhaust. I start to panic and get my dog out of the truck immediatly.

To make a long story shorter. I didn't have the leash and had to call my wife to quickly come down and pick the dog up. All the while I'm standing there waiting for the truck to go up in flames and watching this puddle grow larger and larger. She showed up and I ran across the street to an Ace hardware quickly purchased two large had tanks, some house to siphon with, some fuel line, and a screws driver. I ran back, siphoned out 10 gallons and the leaks all completely stopped. The tank is still half full but there isn't a single drop on my garage door after about a week.

What happened? I have fuel line to replace this small section but I'm assuming as soon as I unhook that hose I'm going to get the other half of the tank pouring out. Is this upper hose for a different portion of the in cab tank? Was the pressure just high enough to show all the cracks and holes? I got this truck about 6 months ago, it's very well taken care of and I've filled the truck a couple times before without this happening.

The black line is the one that leaked like a colander. The tape was me trying things in a panic. Any recommendations for my next step?

[custom10nut]

Time to replace all your rubber lines. They don’t last forever. Fortunately for you, your truck didn’t burn up.
This little rubber hose is necessary for the flex of the fuel line and vibratio.
It’s an easy fix and doesn’t take long.
Just make sure you use fuel grade hose and clamps.

[dflarsen77]

If you don't want the tank to siphon itself empty, your 72 should have a rubber line coming right off the sender (I think they do anyways). Pinch it off completely with some kind of clamp (fuel is the fatter one), and it only leak out what's in the whole line. If it doesn't have that hose, you can just take the sender out. Same idea of taking away the source. Then I recommend replacing all the rubber lines unless you've done them yourself recently.

Although now that I look at your pic more, it looks like the one leaking is your vent or return line, the skinnier one. Either way, the idea is the same, cut of the source, replace the rubber lines. And don't take a smoke a break while you're doing it!

[GMCPaul]

Thank the EPA and our government, old rubber fuel hose will dissolve with the E10 ethanol we are stuck with today.
A fix is PTFE style performance hose and the special fittings required to use the hose
The ethanol is also causing steel fuel lines to corrode and will corrode brass & cause lead & tin solder to break down and fail.
Paul Jr @ GMCPauls

[Andy4639]

One more suggestion. When you do this set a fan up at the front of the truck blowing the fumes to the rear are vise versa depending on how it's parked. Let the truck be cold.
Take some vise grips and clamp the old hose coming from tank. Take the other old end off. Put new clamps on new hose and tighten the one end and have the other ready. Loosen the other old clamp and pull it off and replace with new hose quickly. Tighten new clamp and your done.

[72c20customcamper]

Originally Posted by GMCPaul

Thank the EPA and our government, old rubber fuel hose will dissolve with the E10 ethanol we are stuck with today.
A fix is PTFE style performance hose and the special fittings required to use the hose
The ethanol is also causing steel fuel lines to corrode and will corrode brass & cause lead & tin solder to break down and fail.
Paul Jr @ GMCPauls

This is why I'm glad we have non ethanol high test in my area. But I still use gates barricade carborated fuel line. The

[Fuggers]

Thanks guys. I feel incredibly lucky my truck didn't burn up. It was just gushing directly onto my hot exhaust. I'll have to search down and replace all the rubber sections.

[geezer#99]

A little fuel on the exhaust is nothing compared to popping the hood and seeing gas boiling on top of the intake!
That’s a heart stopper!
The fuel was spraying out because of the vapour pressure in the tank. The pressure had no where to go since you don’t likely have a vented gas cap.

[Fuggers]

I went to replace the line today, pulled the hose off and no gas came out. I started wondering where it went to and traced it back to what I assume is the fuel pump/sender? It has been replaced and the return line isn't even connected. I don't see a place to connect it anywhere.

What I am assuming is that return line sits higher up on the fuel tank and I filled the gas tank to higher level than I have before and the gas started coming out of the tank from the return line into the tank. If it hadn't leaked at this hose it probably would've come out of the hard line in the engine bay.

I don't believe I have a vented cap, if I just cap this return line will everything still function properly? Im thinking it won't because it can't get air in. Did the previous owner replace with a newer pump that doesn't have a return line? Do I just need a vented cap then I can plug this? Hopefully the pictures help

[geezer#99]

Did you follow the two lines back to the tank?

[Andy4639]

One line on the fuel pump on lower front right side of motor is the supply line to the pump from tank. The other line should go up to the caburator.
Look at the tank inside the truck how many lines coming out of the tank?
If 2 are more find the supply one that runs to the pump on the motor. Then the other 2 can be used for venting. Hook them up any way you want to vent the tank are just loop them together and buy a vented cap.

[Fuggers]

I can't get my seat forward to look at the tank. Underside of the truck has two lines coming out of it from the tank area that run up to the pump on the motor. Upper line doesn't connect to anything anymore at the fuel pump. This is the line that was leaking when I filled the tank all the way up.

Maybe I just cap it under the bed and buy a vented cap? Were the original pumps 3 lines and one was this return line? This is the only explanation but I can't figure out how to it why it hadn't leaked until now. Maybe I just hadn't filled it up high enough

[Andy4639]

Originally Posted by Fuggers

I can't get my seat forward to look at the tank. Underside of the truck has two lines coming out of it that run the the pump on the motor. Upper line doesn't connect to anything anymore at the fuel pump. This is the line that was leaking when I filled the tank all the way up.

Maybe I just cap it under the bed and buy a vented cap? Were the original pumps 3 lines and one was this return line? This is the only explanation but I can't figure out how to it why it hadn't leaked until now. Maybe I just hadn't filled it up high enough

I have never seen a stock fuel pump with 3 lines. As stated. 1 is the supply from tank the other is outlet to carburetor. That other line under the truck is for the charcoal canister I would think.

[Fuggers]

Originally Posted by Andy4639

I have never seen a stock fuel pump with 3 lines. As stated. 1 is the supply from tank the other is outlet to carburetor. That other line under the truck is for the charcoal canister I would think.

Interesting, okay I just assumed it went into a fuel pump for a return line. Your diagram suggest it's a lower vent line (in my truck there are two lines coming out of that floorboard grommet) but as you can see in the second set of pictures it used to have a clamp on it at some point. There is only one line into the pump then hardlined almost all the way to the carb. It seems silly they would go through the trouble of venting all the way to the engine bay with hard-line just to leave it open, unless this is what the charcoal canister would be for. I've never heard of it but will do some googling. I think I'll just replace that section of line and be careful not to fill the tank too full for now.

I appreciate your help, thanks

[Pro299]

Yeah, you're looking at the lines for the evap system. Today I started the process of unhooking everything to do a crate engine swap on my 72. I noticed the extra lines beside the fuel supply line itself. At first I thought the evap canister was hooked up, but turns out someone had cut and tapped off the lines at some point in the past. I'll get a new canister and hook up the lines before I drop in the new engine.

[Fuggers]

Originally Posted by Pro299

Yeah, you're looking at the lines for the evap system. Today I started the process of unhooking everything to do a crate engine swap on my 72. I noticed the extra lines beside the fuel supply line itself. At first I thought the evap canister was hooked up, but turns out someone had cut and tapped off the lines at some point in the past. I'll get a new canister and hook up the lines before I drop in the new engine.

Thanks. Now I know what I'm looking for. I'm just surprised at the amount of had that came out of this line after filling my tank all the way up. Would an evap canister have prevented that I wonder?

[RichardJ]

O'Reily offers 3 pumps for a 72 C20. This one has the return line and seems line the better solution.

[Fuggers]

If the previous owner replaced with a fuel pump that doesn't have the return line where is that excess gas going now? Out the exhaust? Excuse my ignorance

[Andy4639]

67 trucks had one line coming out of the tank. The 71-72 models had two lines. One was supply the other a vent that had the canister line that I think you are seeing under the truck. Look under your battery and see if the canister is there are the bracket. Most people just do away with them.
Me, I would take the hose loose at the tank and would cap it off and buy a vent gas cap.

[Fuggers]

Originally Posted by Andy4639

67 trucks had one line coming out of the tank. The 71-72 models had two lines. One was supply the other a vent that had the canister line that I think you are seeing under the truck. Look under your battery and see if the canister is there are the bracket. Most people just do away with them.
Me, I would take the hose loose at the tank and would cap it off and buy a vent gas cap.

Yeah I think you're right. There isn't a canister or a bracket but it clearly used to connect to something. Any idea why has would come pouring out of this line though? Even if the rubber hose hadn't been leaking wouldn't the gas just have come out where the canister used to be? Is there supposed to be some sort of way to prevent gas from reaching this vent line inside my tank I guess is my question?

[Andy4639]

Originally Posted by Fuggers

Yeah I think you're right. There isn't a canister or a bracket but it clearly used to connect to something. Any idea why has would come pouring out of this line though? Even if the rubber hose hadn't been leaking wouldn't the gas just have come out where the canister used to be? Is there supposed to be some sort of way to prevent gas from reaching this vent line inside my tank I guess is my question?

No for the short answer.

The line is open all the way up to the motor so unless you put pressure on it it only got what was sloshed up into the hose which couldn't be a lot.

[Pro299]

Originally Posted by Fuggers

Yeah I think you're right. There isn't a canister or a bracket but it clearly used to connect to something. Any idea why has would come pouring out of this line though? Even if the rubber hose hadn't been leaking wouldn't the gas just have come out where the canister used to be? Is there supposed to be some sort of way to prevent gas from reaching this vent line inside my tank I guess is my question?

I don't think there should be raw gas getting to the evap canister. It's only supposed to capture the fumes of hydrocarbons from the tank and store them in the charcoal until you start the vehicle and those fumes are sucked into the engine to be burned. Not sure you'll reach a solid answer unless you follow each line from your tank to see if deterioration or shadetree engineering caused the problem.

[Fuggers]

The tank definitely overfilled and was escaping the gas tank through this vent hose. It filled more than any previous fill up and the extreme leak didn't stop until I siphoned 2 5 gallon cans out of the tank in the parking lot.

I really appreciate the help guys, I'll replace this small rubber section and be careful not to fill the tank to an extreme level

[darrellyates]

Originally Posted by GMCPaul

Thank the EPA and our government, old rubber fuel hose will dissolve with the E10 ethanol we are stuck with today.
A fix is PTFE style performance hose and the special fittings required to use the hose
The ethanol is also causing steel fuel lines to corrode and will corrode brass & cause lead & tin solder to break down and fail.
Paul Jr @ GMCPauls

PTFE hose is normally just PTFE (commonly known as teflon) in another carrier. PTFE by itself can't be used for a hose, it isn't an elastomer or flexible, so it depends what carrier it's in. Usually, today, it's in a nylon carrier which is an excellent polymer for fuel resistance, including ethanol fuels.

For modern rubber fuel hose, make sure it's Viton rubber. That's a synthetic that's resistant to ethanol. Most are marked as not only fuel line, but E85 compatible (E85 is 15% ethanol, which is the highest commonly manufactured I believe).

This post is correct, ethanol in gas will dissolve most any other rubber including EPDM, and latex based rubber products.

I've even seen radiator hose used as fuel neck connecting hose, and of course vacuum lines used for gas tank vents, and heater hose for fuel lines. Will swell, degrade, dissolve in a matter of weeks not years.