Sending unit question • The Dodge Challenger Message Board

by **MLMFLCN** » 19 Jun 2008 0:52

My sending unit has two outlets outside of the gas tank. I've got the 3/8th inch line running to the carb, is the other for venting? I have seen a venting line running from the fuel filler tube down to the sending unit in the tank. Is this necessary? Car runs without it, but put gas in today, just above a ½ tank, and of course since I forgot to block off the second line, and the fact the gas expands in the tank, I got to clean my garage floor when I got home. My filler tube is not drilled out, and I really don't want to unless it is necessary.

My real question is, can I just block off this line with a small piece of hose and some clamps, and just drive the car? Just want to be certain I am not doing any damage. Thanks all.

by **patrick** » 19 Jun 2008 5:01

Just get a vented gas cap. :wink:

by **dave-r** » 19 Jun 2008 8:06

I think it is actually a fuel return line. Like Pat says, block it off and use a vented cap (if the filler tube is not vented near the top just inside the quarter panel) or you could run a line from that small pipe up higher than the tank so that it does not spill fuel.

by **MLMFLCN** » 19 Jun 2008 11:11

Thanks Dave and Patrick. I searched the normal places (Year One, Mancini, Jacks, etc.) but did not see a vented gas cap listed. Mine is a 1972 Challenger. Any thoughts on a source for this?

Thanks,

- rich

by **MLMFLCN** » 19 Jun 2008 11:33

Here is what I've got. Would like to keep the same look / set up if possible. Thanks again.

by **dave-r** » 19 Jun 2008 11:40

With that type you would have problems unless you can drill a hole up through the middle?

Are you sure you don't have a vent on the filler tube or on the tank?

by **MLMFLCN** » 19 Jun 2008 11:46

No, I have seen the vents on filler tube on other cars, inside the quarter panel, mine does not have this. My original tank had the ECS set up, but I moved to one without (1970 I believe).

If I go to a flip top, can the inner cap then be vented? If I drill this one out, do you go right through the body color and the "center" of the cap? Thanks Dave.

by **MLMFLCN** » 19 Jun 2008 11:50

Dave,

On your other point, earlier on, about just venting to a higher point, would this be a better solution? The gas was really pushing out last night, and it was defying gravity with all the pressure.

by **dave-r** » 19 Jun 2008 12:12

I am not sure on the exact construction on that cap but is there not a gap between the center bit on the spring and the outside body of the cap?

You don't have to drill to the outside of the car. Just to the other side of the cap seal.

by **dave-r** » 19 Jun 2008 12:20

MLMFLCN wrote:Dave,

On your other point, earlier on, about just venting to a higher point, would this be a better solution? The gas was really pushing out last night, and it was defying gravity with all the pressure.

Just had a rare moment of clarity.

Not sure if venting is the problem here.
Without a vent you get negative pressure in the tank as air cannot get in to replace the fuel being pumped out. So the tank can possible collapse due to negative pressure.

I am not sure what would push the fuel out....

by **MLMFLCN** » 19 Jun 2008 15:20

I have been driving the car for a few weeks, with only 3 - 5 gallons in the tank. Until I nearly filled it, there was no issue.

I am not certain how far into the tank that "second" line goes, but it most likely was below the line when I filled the car. So when I say pushing, that may have been a stretch. I will take a picture of what it looks like tonight and post.

It had a slight drip prior to driving, I then drove the car a few miles. When I parked it in my driveway, it was coming out at a much greater rate. Installed a short piece of hose onto the outlet, and drained it into a gas can. It "siphoned" out about 1 gallon or so, maybe a little more, then stopped on its own. Gauge showed a little more than ½ tank.

From reading other threads here, if I did not have this "vent" line on the sending unit, I'm not sure the car would not run. I am hopeful that drilling out the gas cap will provide the same effect, and then just block off the extra line out.

by **dave-r** » 19 Jun 2008 17:05

You probably just filled the tank to a level above the pipe. It only goes in about an inch I think?

by **Moparman1972** » 28 Jun 2008 0:37

I just installed a sending unit, and yes, it only goes an inch in, so it will spill if you fill it over halfway or you take a hard righthand corner. It is probably a return line, but since I do not have a vented cap, I ran a vent line from it to above the top of my filler neck in the trunk. This way, the vent is above the level of the tank and the filler neck, so I cannot pump gas into the trunk by filling up the filler neck and forcing gas out the vent instead of it spilling out the neck for me to see.

Hope that helps.

by **MLMFLCN** » 28 Jun 2008 13:14

Moparman 1972. thanks for the advice. Any chance of posting a picture to show how you set up? Thanks again.

- rich

by **Moparman1972** » 28 Jun 2008 13:42

Tough to get pictures without a camera, but basically I ran rubber fuel line from the vent tube right below my gas line and brought it up through the hole in the trunk where all the hoses, etc were for my california emissions package. I threw a breather on the end of it, too. You could probably do a much cleaner job routing it in the trunk, but I dont know how.

by **MLMFLCN** » 28 Jun 2008 14:45

Cool. Thanks Moparman. Where did you get the breather?

by **Moparman1972** » 29 Jun 2008 0:54

Just a little breather from Auto Zone or Advance Auto, cant remember. Used a hose clamp and zip ties to put the breather on, then hold the hose above the filler neck. I plan to do it more permanently when I have time. Good luck!