Fuel leak issue.

[70 RR]

I bought a 1970 Roadrunner recently and I have an issue with a fuel leak. The car has a new tank, new lines and sending unit. I don't like to mess with fuel tanks so I took it to a mechanic friend of mine and he told me that the sending unit had a return line and that my car didn't require one. He plugged the hose and I though my problem was solved. My driveway is on a slight hill and if I back the car in (with the front of the car lower than the back) the tank begins to leak. The thing that has me baffled is that it doesn't leak until about 10-15 minutes elapse. Is this because pressure has built in the tank? Aside from dropping the tank, is there anything else to check for? It seems like it is coming from the return line but I can't say for sure. The cap is not vented and I don't think a vented cap would work due to the location of the filler neck, am I right? I have a 440ci 6bbl and I am wondering if I should just get a sending unit without the return line. The problem with that is the only sending unit I can find without a return is a 5/16" and I believe I need at least a 3/8". Any thoughts?

 

[Propwash]

Best bet would be to get under there and look to see where it is running out. The crappy aftermarket sending unit retaining ring and seal are known to leak now days, so that would be another place to look. The retaining ring tends to be too loose and about the only fix is bending down the three slide lock tab's on the tank itself so it puts more pressure on the retaining ring and seal. There is a lip around the sending unit, as well as a lip/seam around the mid point of the tank where fuel could gather before starting to drip down. Maybe that is a possibility? I wouldn't imagine pressure is building up in the tank if your vent lines are free and clear. As far as your gas cap, it is non-vented and leave it that way. You'll have fuel all over the place if you put on a vented cap, being it's location. Anyways, take a peak under the car....Tighten up any hose clamps under there and see what it does from there. Good luck

 

[70 RR]

Thanks, do you happen to know where the vent tubes are supposed to vent to?

Best bet would be to get under there and look to see where it is running out. The crappy aftermarket sending unit retaining ring and seal are known to leak now days, so that would be another place to look. The retaining ring tends to be too loose and about the only fix is bending down the three slide lock tab's on the tank itself so it puts more pressure on the retaining ring and seal. There is a lip around the sending unit, as well as a lip/seam around the mid point of the tank where fuel could gather before starting to drip down. Maybe that is a possibility? I wouldn't imagine pressure is building up in the tank if your vent lines are free and clear. As far as your gas cap, it is non-vented and leave it that way. You'll have fuel all over the place if you put on a vented cap, being it's location. Anyways, take a peak under the car....Tighten up any hose clamps under there and see what it does from there. Good luck

 

[70 RR]

Thanks, I will check all connections and the retaining ring.

 

[WileE]

Go to Herb's, or one of the Mopar vendor & get the proper gas tank vent set.

 

[440+6]

All 440 and hemi's had the 1/4 inch return line.

 

[Propwash]

Thanks, do you happen to know where the vent tubes are supposed to vent to?

You have (2) Vent lines....The ports are located in the front upper left corner of your fuel tank. The port to the inside has a vent line shaped like a "U" and tucks in next to your shock crossmember. Your port on the outside has a vent line that runs up through the trunk floor, to the right towards the right inner wheel well, takes a u turn and then goes back through the trunk floor, dumping into your right frame rail. Lotta different folks sell the vent line set if you're looking for them...Classic Ind., Year One, Megaparts, Fine Lines, Inline tube, Right Stuff Detailing, like WileE mentioned "Herbs" and many others.

 

[193rdsow]

Just went through this issue with my '69 RR. Prop wash is spot on with reference to the vent lines. The previous owner had my vent lines installed backwards on one side and had nothing on the left vent. I filled up and spilled several gallons out the vent. You can simply use rubber fuel line as vent line. Be sure though, that the vent line going into he trunk, is on the right vent tube.

 

[Dennis H]

Same issue. 69 Coronet R/T. Nose down leaked. Rerouted the vent in the forward part of the tank higher into the trunk. Solved.

 

[70 RR]

Ok, first off I want to thank everyone for the replies. The return line on my sending unit is currently blocked off with a bolt and a clamp, is this OK to do or is there another application? When I got the car two months ago, the return line had an 8'' open hose pointing at the floor of the car and it seemed to be the source of my leak. I was told that the only cars that had the charcoal canister that the return line went to were California cars in 1970. Whats the deal on that? I will check my vent tubes and go from there. Tired of losing fuel, its expensive and dangerous!

 

[70 RR]

Ok, so I just got out from under the car and the outside vent tube is connected to the line that goes into the trunk and the left to the other line to the frame. It seems that my issue is with that return line on the sending unit. I am told that my car requires at least a 3/8'' sending unit because of the 440+6 and all 3/8'' sending units have the return. What next? Where do these vent lines end up, are they just open lines or do they end up in some kind of filter?

 

[70 RR]

View attachment 126222 Vent tubes. Right the lower line (outside line) goes up into the trunk and then back down. The other goes into the frame. If you notice the area where the undercoating is missing, that is where the original hose coming off the return line that was uncapped was shooting fuel against the under panel of the car. We thought plugging that return line would solve the problem.


View attachment 126223 This is the return line that is blocked off.

- - - Updated - - -

An image I found in my service manual.

 

[Propwash]

Those vents do not go into any kind of filter. Just open to the air. Your return for your tank is a vapor return line on your 44+6 system. If you run that system, you'll need a fuel vapor canister. Below is a good thread that points a few things out with that type of system. One benefit of a return type system is drastically reducing the chance of vapor lock/fuel boil because the fuel is not deadheaded and sitting up at the carb(s) when not being used. You're car will run without that setup. More folks around here running 440+ engines around here don't have them, but definitely are a good addition. If you're not going to use it, cap it off with a hunk of 1/4" rubber fuel hose, a bolt and a hose clamp. Good luck.

http://www.1970chargerregistry.com/mboard/index.php?topic=271.0

 

[70 RR]

Thanks for your advice. I noticed the vent tube that enters the trunk was bent at about 45 degrees instead of 90 and l adjusted it. The vent tube is plugged and so far so good. I have yet to go beyond 3/4 of a tank, l am a little gun shy!

 

[Propwash]

Hey no problem. Glad to hear you're up and running leak free.

 

[D575]

http://www.forbbodiesonly.com/mopar...1-Gas-tank-venting-issues&highlight=fuel+leak

 

[bigmanjbmopar]

I was going to suggest get the correct sending unit one with out a return line, easy to change on a low tank.