Classic/Antique Car Repair: Fuel sending unit function, 1967 jeepster commando, gal fuel tank

Question
I have a 1967 Jeepster Commando with a V-6. It has the original 15 gal. fuel tank and sending unit. I had the sending unit checked and was told it registered 87 ohms empty and 2 ohms full. I installed an aftermarket gauge but it will only register 3/4 to full. When the ignition is off the gauge dial goes to the full range instead of to the empty range as in traditional setups. I was told by a mechanic that the sending unit would have to be re-calibrated to match the gauge. Can that be done or do I have to buy a new sending unit and matching gauge ?  

Answer
You don't say why you changed the dash indicator, so I  assume there was some failure with the original indicator.

If this is the case, you will have to also have a matching sender installed in your tank - the resistance range for the old sender is not right for your new dash indicator.

I am not exactly clear what you mean by it only indicating 3/4 to full - but I take that to mean that when the tank is empty it reads 3/4 full, and when the tank is full it reads full.   If this is the case, your sender is just covering the wrong resistance range for the indicator - the new indicator should have come with some instructions as to the proper resistance range for it to work properly - and you'll have to comply with that by getting the right sender to work with it.  If you can't find that information, you can determine it by using a variable resistor (AKA potentiometer) and an ohmmeter to experiment with the new dash unit, to see what resistance value is required for the various dash readings.

As for the needle going to "full" when the key is off, this is just a design characteristic of the new unit you bought - it does not indicate a problem.

Since your original sender seems to be working fine, I'd think you'd rather find a replacement dash unit which is right for your car.  Have you exhausted the parts sources for your vehicle?  Try a Google search for "jeepster parts" or the like - to see what you can come up with .  There are user enthusiast groups for every vehicle ever made, and you'll find the folks there are knowledgeable, helpful and friendly.  I think you will be referred to a source for a replacement dash indicator, or perhaps someone who can repair it for you.   In the meantime, drive by watching your odometer - fill it with gas every 150 miles, and you'll never run out!

Good Luck,

Dick.