Unusal Temperature Gauge

Hi all.
I have a issue and it has been bugging me for a few months now.
TD5 on a 01 plate has a unusual temperature gauge behaviour problem.
On times (On Start Up) the temperature gauge will shoot up to the max and light will show and will continue to do this. Normally after about 30 mins of driving it will resume to normal.
The Wife was worried about this so I changed the temperature unit thinking it was faulty.
Unfortunately this did not solve the issue.
I have installed a inline temperature unit and Gauge into the Top Hose as a precautionary measure to give peace of mind. This seems all ok but the Wife is still unsure and worried that the Disco is boiling (Even from cold start)
I am totally baffled on why this is so wondering if anyone else has had the same issue or can shed some light on the cause of this.
All help appreciated

Your profile suggests that you're talking about a Td5 Disco 2.
The temperature indicator, it's hard to call it a temperature guage is actually driven by the engine ECU, based on the temperature measured by the sensor.
The first things you could check are the two connectors to the ECU. As you say, you've installed a separate temperature guage which will give a a much more sensible reading.

The ecu gets a signal from the sender when the contacts in it close and let the current through to earth. If you have a short circuit to ground in the wire leading to the sender it will give the same signal to the ecu, so check the wire all the way back from sender as far as you possible can, looking for damage that allows the conductor to touch the engine, brackets, bodywork etc.