I only used this site once before, so I'm still new. What is the normal position of the fuel (gas) gauge when the key is off on a 72 cutlass. Is it suppose to fall to empty when key is off and rise after key is on or does it stay at the position is tank level is at (ex 1/2 full) when the key is turned off.
Hope someone can answer.


Herv

 

There is no normal position. The gauge only functions when the key is ON and current is passing through it. It can come to rest anywhere when the power is off. As long as it is reading correctly when the ignition is on, it's working fine, and there is nothing to worry about.

 

This just started but when I fill my tank the gauge goes way past full. I drained out 10 of the 20 gallons and the gauge now reads 3/4 and it stays there after the key is turned off which should be 1/2. I believe it is working but the indicator is off??

 

Have you read the owner's manual for your car?

Page 24 of the 1972 Cutlass owner's manual. Note what is says in the left-most column, under Fuel Gauge, second sentence. The implied meaning is that, if the ignition is not ON, the gauge reading doesn't mean anything.

 

Again, pay NO attention to what the gauge does when the key is off. The gauge is just an ohmmeter, and it requires electric current to work. Without it, it cannot read anything.

Note also what is says in the FIRST sentence under Fuel Gauge in the owner's manual. These gauges back then were approximations. We should not expect in gas gauges of that era the precision we seem to think we have in gas gauges in today's cars.

How far past F does your needle go? Having it go past F but then move down as fuel is used up is pretty much all you can expect. I had a '73 Custom Cruiser that I sold last December, but its fuel gauge was like this. When I filled the tank, the pointer went about as far past F as the distance between the 3/4 hash mark and the full mark. When the gauge read about 1/4, the tank was nearly empty, and it was time to fill up. So the whole thing was shifted to the right one hash mark, and, once I knew that, I lived with it. After all, I had a working gas gauge.

 

The gauges in these cars are not very accurate. Some gauges will take forever to go from past full to 1/2 and then move rapidly towards E. Its more of a level indicator vs the shape of the tank. When the tank gets below 1/2 youll see the needle fluctuate as the gas moves around the tank. As you get used to how the gauge works vs how many gallons it takes to fill the tank at different levels you'll feel more comfortable with how it works. On most of my older cars I generally fill up when the gauge gets to 1/2. However as long as it is still fluctuating while I drive I know there is gas in there.

 

Since it just started I'm going to drive it and watch the gauge, Prior to this it has always worked properly. Thanks for the info.


Herv

 

Keep in mind, also, that a gauge that goes way past F and stays there regardless of whether the key is ON or not and regardless of how much fuel is in the tank is an indicator of an open in the sending unit circuit. This is a common problem in 40-50 year old sending units.

But if your gauge moves down as fuel is used up, then the sending unit-to-fuel gauge wiring is intact, and the sender is working.

 

If your gauge has worked well to this point and then yesterday it suddenly started behaving funny, then, yes, you might have a problem in the making. As I said, a pointer that goes past F is an indication of high resistance. It could be an indication of a full tank, but it could also be a connector in the wiring or at the sending unit that is starting to go bad or a ground that isn't grounding as well as it should. You could check the ground wire coming from the sending unit and make sure it is securely attached and that the connection is clean and free of crud and rust.

Do you know anything about the history of the sending unit? Has it ever been changed or serviced or anything that you know of? If it's the original sending unit, it wouldn't be unheard of for one that old to have problems or fail outright.

 

I've owned the car for over 10 years and do not know the history. I do have a lift and was able to check I the ground. I had my carb rebuilt and installed it today and noticed the gauge while on a test drive. I was certain it had gas, but I topped it off and it only took a little over 2 gallons. After checking fuses and as much wiring as I could get to I drained off 10 gallons and that is when the gauge dropped from way over full to 3/4. It seems that the gauge itself is off from the way it is acting. I just cannot figure out what caused the problem.

 

It may be worn out and sticking, its just a float on the end of a metal rod, hooked to a rheostat. It could be time for a new one. They can be had through any auto parts store.

 

I second this. It may just be your sending unit's time. Nothing lasts forever. There are quick, simple tests you can do to check the wiring and the operation of the dash gauge itself, and if those tests are passed and the gauge still behaves oddly, it's probably the sending unit.