cbartonbrown

My gauge on my 67 Supreme reads 3/4 when the tank is half full (10 gal) and reads 3/8 when it is near empty. I learned the latter information the hard way. The fuel-reading system used to be good.


Do you think it's the sending unit?



Is the sending unit on top of the tank? If yes, how do you remove/test the wire at the sending unit for testing?


where are the wires running to the sending unit? In the trunk?


Thanks, everybody.

jaunty75

I would suspect the sending unit.

Do you have a '67 Olds Chassis Service Manual? See Figure 8-5 on page 8-4. The sending unit on a Cutlass is located on the opposite end of the tank from the filler neck. You'll have to jack up the car and get down under it. The sending unit should be accessible without dropping the tank. There are two wires coming off the sending unit. One wire is a ground connection that attaches to the body at some point near the sending unit, and the other wire goes to the gauge at the front of the car. The service manual says "Disconnect gauge wire at tank unit," so I'm assuming it can be disconnected right there.

With only the ground wire disconnected, turn the key ON and observe the gauge. It should go to F or well past it. That's an indication of an open circuit, and that's what you have with the ground wire disconnected. Next, ground the gauge wire you removed from the sending unit, turn the key ON, and observe the gauge. It should go to E. That's an indication of a short-circuit, which is what you have when you ground the sending unit wire.

If the gauge passes both of these tests, there is no problem with the dash gauge or the wiring to it. The next step is to remove the sending unit and test it. Put an ohmmeter across the leads, and it should read 90 ohms when in the full "up" (tank full) position and zero ohms when in the full down (tank empty) position. It may need cleaning or adjustment.


I would normally suggest that, if you're going to remove the sending unit, you might as well just put in a new one. However, I don't know that new ones are available. I checked rockauto just now, and they don't show one for a '67 Cutlass. I have not checked any other sources.

oldcutlass

Rockauto shows 6 different ones for a 67 Cutlass depending on fuel line requirements:
https://www.rockauto.com/en/catalog/...ding+unit,4436

jaunty75

Interesting. You looked under "Cutlass" while I looked under "Cutlass Supreme." If you look under the latter at the rockauto site, no sending units are shown. Shame on rockauto!




Given this, I go back to my first notion. The sending units are all only about $35. Get a new one, install that, and be done with it.

oldcutlass

No, I do not think your sender is bad, it just the way it works and the same as mine. None of them were too accurate back then other than full or empty, anything in between was a guess because of the shape of the tank.

Also when you get below 1/2 the needle starts to fluctuate when you make turns or brake, this is also normal. As long as its fluctuating you have fuel going towards E, when the fluctuating stops, so does your engine as you are out of fuel.

jaunty75

But he says that it "used to be good" and apparently only recently started showing 3/4 when it was actually 1/2, 3/8 when it was actually empty, and the car left him high and dry once because of this. It seems that something has changed.

oldcutlass

I've had multiple 67 Abodies and they all acted the same. Mine runs out of fuel just at E, but note that 1/2 is not 1/2.

cbartonbrown

Thanks, everybody. This is all very helpful. I'll test the wiring and gauge as stated above. It sounds easy and i like working on her.



If i remove the sending unit, i will be just as happy to replace it.


OPGI has one- https://www.opgi.com/cutlass/PZ00732/ but there are 2 tube diameters- 5/16 and 3/8. The OPGI guy said 300 cubes+ is 3/8. But i will try to measure (it's a small circumference).


Yes, they are probably not so accurate but now it's really inaccurate. i suppose i could fill up at every 1/2 tank- 150 miles.

Koda

Yeah empty back then meant empty. Empty now means 20 more miles to find a gas station.

oldcutlass

If the resistance checks good, all you have to do is bend the arm up a hair so the gauge reads empty when its empty.

cbartonbrown

Thanks, Eric. However, if the gauge reads high (actual is 1/2 but gauge reads 3/4) then shouldn't it be bent up? Just checking.

oldcutlass

That's what I said in the previous post. Bending the arm up lets it go lower. Its a potentiometer attached to an arm that varies resistance based on fuel level. The arm is registering higher at both top and bottom ends of the scale. You are changing the position of the scale.

meoff

cbartonbrown

Thansk, Eric. i agree. i mis-read your first post. Thanks as always for your great knowledge and articulate explanations.

1967Supreeeme

cbartonbrown

Tiberian Fiend

Use a chisel (or similar) and a hammer to turn the ring at the ears. Go around tapping each lightly and be extra careful not to shear them off or you're really screwed. I changed the sending unit in my tank, and I still have a similar problem with the gauge you do, so it may not help to change it. I think I'm going to get my gauge rebuilt.

cbartonbrown

Tiberian Friend- Thanks for the advice. There are lots of working parts to this problem, aren't there? If my new sender doesn't fix the problem i'm going to try (other) Eric's advice and bend the arm. This bending procedure sounds like a real time-suck though- trial and error. I'll report the results.



Charlie