My 2006 VDP is slow to warm up. Once it's up to the correct operating temp. it stays exactly where it should. Thermostat perhaps sticking open? I'd appreciate some input on this before pulling it apart. Thanks guys!

 

Im getting this on a 2004 VDP I thought of stuck thermostat as well. The temp dips below where it should be on a cold night and high speed

 

Compared to my X308 XJR I found my 2004 XJ8 slow to warm up as well and though it might be one of the reasons for the poor heat output of the climate control (I had to replace the heater matrix in the end).

I plugged an OBDII reader in and monitored the temperature and it was actually going up a lot quicker than the gauge was showing so in my case the gauge is just not reflecting reality.

 

It might be the auxiliary coolant pump.