70 ctls

Hi Guys,
Need an education about the second line. I have a bad ground and/or sending unit. Upon initial inspection note that the unit is a 2 line one............ but the second nipple is unconnected and just venting at the front of the tank right under the floorboard. Think I know that it should go to the third fitting on the fuel pump. However, the fuel pump has been replaced with a unit with one in and one out.
Questions are:
1. What is the original design intent ... an over flow return ?
2. Should I replace the sending unit with single line because of present fuel pump, or replace pump to accommodate a dual sending unit ?
3. Does the second line pal- up with the primary line ? for I haven't found it yet.
My present configuration is unsafe - correct?

Thanks and I know you guys know,

70 ctls

MDchanic

If your car has the second line running along the frame, then there is no reason not to use it, and, since fuel pumps are cheap, I'd install a pump with a return fitting.

If your car does not have a second line, then you'd have to run one, which would be a major pain for minimal gain, so I'd skip it and cap the extra nipple on the sender.

The intention of having a supply and a return line, in your car as in cars made today, is to maintain a flow of cool gas to the fuel pump. During very hot conditions, such as stop and go summer traffic, the fuel in the line can vaporize, leading to vapor lock, which prevents the pump from pumping and the car from running. By pumping a constant flow of gas out of the tank, around, and back again, the gas in the lines is always cool, and doesn't evaporate.
In the late sixties to early seventies, car manufacturers began using the second line first on cars that would be expected to get the hottest (high performance and A/C cars), and then included them on more and more cars, until by the mid-seventies they pretty much all had them.
I do not recall which exact cars got them in 1970, but you can tell just by looking.

- Eric

70 ctls

Thanks for the info Eric. I'll look further to see if the second line exists and take it from there.

John

Allan R

Easy to tell. Look under the car on the right side inner frame rail. There will be either 1 or 2 lines running along there back towards the duel tank.