Datsun Roadster Forum-311s.org

Fellow members,

Hello, My Name is Dave Oppenheim, and I Recently purchased a 1968 datsun roadster 2000. The temp gauge wasn't working and the fuel gauge needle was floating at half a tank. I changed out the temp. sending unit, thermostat housing, water outlet and put in a new drop voltage regulator. Temp. gauge now works as it should, but fuel gauge needle goes up just a smidge past the E (empty) mark on the gauge when I turn the ignition on or star up engine. I thought at first that maybe...or hopefully, I do have an empty gas tank. So, I went to the gas station and put in almost 6 gallons of gas and the tank was FULL. I opened up the access panel to the fuel sending unit and removed the wire connectors. I lightly sanded the tarnish off of the brass or copper nipples and reconnected the wire connectors to the nipples. I still have the same reading on the fuel gauge where the needle moves up to the E mark and then stops. Does anybody know what's going on or what I should do? Should I take the fuel sending unit out? And can I take the fuel sending unit out with a full tank of gas? Any suggestions will be greatly appreciated.

Dave Oppenheim

You have gotten a good start on what to check. First- do the following only if there are no fuel fumes or vapors!!
With the access panel off, (key on!) ground out the two wires (one of them will do it, just don't know which) and watch the fuel guage. If it goes up past full, it's probably the sending unit. If it doesn't go any farther than it has been, it's probably either a wiring issue (bad ground, poor connection etc.) or the guage is bad.

In theory, you are actually safer with a full tank than a mostly empty tank as the fumes are the most volatile. However, the tank is easily drained as there is a plug at the bottom for this purpose. I'd drain it and let it air out for about a year - but then I am more than a little paranoid!

If it fails the test, then the sender is usually easy to remove, use a brass drift and mallet or a basin wrench to rotate the lock ring. A few drops of penetrant on the ring may help.Vacuum or blow out any loose dust rust etc before lifting out the sender. Once it's out, take a look in the tank, see how clean it is, then cover the hole to keep debris out. The internal sender parts can be delicate, so clean gently. Once it's in hand, you can check it with an ohmmeter. It is adjustable by moving the little contact, it will make sense when you see it, but be very gentle.
Unless it's perfect, replace the O ring, and if it's banged up, the lock ring.

Have you checked the wire connection on the gauge? my 68 1600 did the same (intermittent) and I secured the wire/lug on the gauge and it works great now.

Fuel gauge sending units have an element that reads approx 83 ohms when empty and 16 ohms when full. (give or take a couple of ohms)

If the gauge is moving to half scale but does not change with the fuel level then it's probably good so it might be time to check the wire from the gauge to the sender. Don't forget to check the ground on the sending unit as it is a critical part of that circuit.

Jon

caraddict wrote:Fuel gauge sending units have an element that reads approx 83 ohms when empty and 16 ohms when full. (give or take a couple of ohms)

If the gauge is moving to half scale but does not change with the fuel level then it's probably good so it might be time to check the wire from the gauge to the sender. Don't forget to check the ground on the sending unit as it is a critical part of that circuit.

Jon

As Jon said, with only a 60 ohm difference all connections need to be 100% clean.