Fuel Tank Sending Unit, One tube or Two?

[Blueheeler]

Sadly, I've come to the conclusion that my fuel sending unit is bad. Gauge is fixed at the 3:00 position & after checking the ground & the brown wire feeding into the trunk area problem still exists. 

MY issue is trying to purchase a new sending unit it looks like a one pipe (tube) sending unit is the most popular, but my tank has two pipes. (tubes) Car's a 1970 350CI 4BB. I'd like to order the correct sending unit, but I'm confused. ANY advice on which one to order.

[cny first gen 71]

I got mine from opg, factory duplicate but make sure you call first make sure it's in stock. I also got one at advance auto but not a factory duplicate  and I didn't use it. Also I have to take it back out and bend the arm because it does not read accurately. The replacement are not no where near the quality of oem parts but good luck finding one of them. The job itself isn't real bad but you want to run as much gas out of it as possible so it's not so heavy. 

[MC1of80]

Stick your head under the car and physically look at the fuel line/s coming out of the tank. 70s usually have one 3/8 line. 

If you don't feel like waiting for opg, we just put one in tom71 Monte Carlo Saturday. He purchased it from Ground up. Just make sure you get the 3/8 fuel line and NOT the 5/16. The 3/8 sender was used in big block Chevelle applications. All first Gen Monte Carlos use the 3/8 fuel sending unit and fuel lines. 

[Mike Brichta]

I purchased a new one from Ground Up a few months ago and after installing it, I realized that the new unit was bad. So I had to get another one and replace it all over again. I would strongly suggest that you bench test the new unit before installing it. YouTube videos tell you how to do it.

Also, if you have another sending unit around that works, I would use it to test for sure that the existing unit is bad and not the gauge in the dash or some other wiring issue. Could save you lots of work chasing the wrong problem. Maybe you could borrow one that works from a buddy. I have a few around that I use for this type of thing.

Hope that helps! Good luck.

Mike

[MC1of80]

To test the gauge itself, unplug it in the trunk. With the key on, Ground the wire, a test light will work. Do not look for a light!  The gauge should move towards empty. Disconnect the ground and the gauge should go past full. 

Before installing the new sender, plug it in, ground the wire on the sender and with the key on, move the lever/ float. Up is full, down is empty. Observe the gauge again. 

[71MonteCarloMD]

+1 to what Thomas shared as I tested that way to determine to replace mine when I first got the Monte Carlo.

[sbarnette]

On Sunday I drove my 71 for the first time since my surgery in December. As soon as I started her up, the gas gage went to 3:00 o’clock. I guess I’m chasing the same gremlin!

[72-CLASSIC_RIDE]

4 hours ago, sbarnette said:

On Sunday I drove my 71 for the first time since my surgery in December. As soon as I started her up, the gas gage went to 3:00 o’clock. I guess I’m chasing the same gremlin!

This had been a problem for me when I purchased my 72, but did not understand why at times did work while other times didn't.  Not my daily driver so after sitting awhile, gauge would start acting up and finally realized there was corrosion on Fuel Sender Unit causing Fuel Sender to stop moving.  I would take car out and slosh fuel in tank by revving motor, rocking car back and forth until gauge reacted and over time, no more problems.  Since I have used the fuel stabilizer to help keep moisture out.  Might be worth a shot checking before pulling tank.  I believe if vehicle sits for a period of time, this issue is probably somewhat common for older cars and has been over 13 years since that issue surfaced.

Doug