The 'E' Type Forum

What can cause the gauge/needle to move between E and F very slowly?
I filled the tank, which was reading empty, but would only take about 1/4. The needle remained at E. I tapped the glass, but unlike another Jaguar, where this will send the needle to the correct level ver fast, this gaugeś needle moved up to about 3/4 very slowly. A few mins later the needle creeped back to about 1/2. I tapped the glass again and the needle moves up a bit. 5 mins later it showed just about F, only to creep back after a few mins, to perhaps 2/3.
Shall I try another instrument/gauge, or is itba grounding issue? Not the sender I think.
Something with the Ohm figure perhaps?
Never seen this on any of my many Jaguars in the last 35 years....

A faulty voltage regulator.

I'd suggest replacing the voltage regulator first, either by substitution or by taking up Rory's offer under the E type upgrades section of free parts to build your own Solid State instrument voltage regulator.

If it were the voltage regulator, then the water temperature gauge would also be affected, as they share the same power source, but that has not also been reported a problem.

The needle movement is gradual because the gauge has a bimetallic strip in it which takes time to heat up and cool down.

To help diagnose it, swap the signal feed to the water gauge (green/blue) and the fuel gauge (white/green?) and see whether the fault swaps over. If it does, then the problem is before the gauge. If it does not swap to the other gauge, then the problem is with the gauge or somewhere up to its power source. If both gauges are affected equally, then it is a wire or connection or component common to both.

Most likely, you will find a broken connection on the fuel sender circuit or at the sender itself.

The relevant ground connection and the gauge's wire to the power source are both parts of the circuit that can affect that gauge.

kind regards
Marek