Somewhere under the dash should be a capacitor or something to keep the fuel level reading steady instead of having the gauge move with every movement of the fuel in the tank. What my truck does is when I first turn the key on I get what I believe to be an accurate reading. After a minute or so the level slowly goes down to a lesser reading. As capacitors age they develop internal resistance problems, leakage, and open circuits. I know that much. I guess I am asking exactly where this is found in a 65 and if it sounds like this may be my problem. I'm tired of riding on a high pucker factor thinking I'm low on fuel when I really am not.....

 

The resistance comes to play in your tank sending unit clean the connections for a good ground. You might need to replce your fuel sending unit. Check guage by connecting a good ground at tank wire turn key the guage should read full. Hope this helps.

 

There is no capacitor as you are refering. There is a Voltage regulator attached to the back of the dash that steps the voltage down for the guages.
I'd suggest removing the sending unit and cleaning the wiper arm and checking the float. Attach a good ground jumper and move the float up and down. The guage will peg out when up and fall when lowered. If your still having trouble, replace the regulator.

 

Are you sure about the voltage regulator theory? The gauges should be 12 volt gauges. Any gauge I have ever sold are 12 volt and none require a "regulator" or any kind of resistor which is what it would take to reduce voltage. Now, if you had an old 6 volt vehicle and upgraded to a 12 volt system you would need such a component to keep from harming the gauges.

Think about this. If you have a variable resistor floating in liquid directly connected to a gauge reading changes in resistance based on float position while riding down the road the gauge needle would be all over the place. Every bump in the road or sway of the vehicle would cause a dramatic change in reading. Correct?

The Germans call the solution to this problem a fuel gauge vibrator. When my 69 VW had a bad one the gauge did what I previously mentioned. Just like an old Chevy. I work in parts and used to work in repair and have found that not many folks know that such devices are present in the electrical system. It's not a foreign car thing either. I have noticed them in American car wiring diagrams as well. I'm not saying that all vehicles have this. I don't know. Thats why I asked. As far as electrical theory goes something would need to be incorporated to compensate for random motion of fuel to give a readable reading with some measure of accuracy. Othewise you would have to come to a complete stop, on perfectly level land, and remain perfectly still to get an accurate reading.

Are there any other electronics bugs out there to back me up on this???

 

The thing is a CONSTANT VOLTAGE REGULATOR and is behind instument panel to protect the guages from voltage spikes. Maybe pull sender out of tank to better understand. You will have some guage movement with motion but not as drastic as you describe.

 

OK so the thing is called a constant voltage regulator. That makes it a component that if faulty could be sending incorrect voltage signals to my gauges. Am I right? I only have fuel and temp by the way. The temp gauge seems to read hotter than actual engine temp and also goes all the way to hot every time you crank up after warmup. It only does that for a second and then comes back to slightly above center. I have always thought the sending unit was bad but not bad enough to worry about. Know what I mean?

Maybe this regulator thing is affecting both gauges. Who knows? The device I was mentioning before was only to dampen the fuel gauge reading.

 

I wasnt getting anything from my oil, temp, and fuel guages and after replacing the constant voltage unit all three work perfectly.

 

Has anyone ever taken their gas gauge apart and noticed that there is an adjustment on each end of the scale that are independent of each other. I adjusted mine by first filing the tank from a can until gas is just about to spill over at the filler neck. With the ignition switch in the "on" position adjust the needle on the full (F) side until it rests exactly on the "F" mark. Now turn the ignition switch to the "off" position and adjust the empty side adjustment till the needle rests exactly on the "E" mark. These adjustments are made with a small flat blade pocket screwdriver and there are small holes on the back to acess these adjustments. These tanks hold about 18 gals. so that makes each quater section of the gauge holding about 4 1/2 gals. Just remember that when your gauge is adjusted this way your tank is realy empty when that needle is on the "E" mark. I've refilled the tank when the gauge was on the "1/4" mark and it took exactly 13 1/2 gals. Hope this helps someone
Thanks James