temp gauge shows over heating but rad pipes cool

Hi all
my temp gauge is going quickly into the red since I put a thermostat in today its a disco engine in a defender.
It didn't have a thermostat in since I bought it a month ago and it never had this reading when the gauge is at the red the top and bottom pipe are hardly hot I can hold them in my hand any ideas?

Faulty stat (fairly common from what I've read on here).
Incorrect sender (disco one is incompatible with Defender gauge)
Steve Parker Landrovers sell a sender that will work.
Or fit a whole new gauge/sender combo .

Even if the stat is stuck solid shut the 200tdi will still drive quite some distance before it gets to hot, in my case it was 12 miles before I got home and thought shes a bit toasty!
Ebay Tim capilliary temperature gauge, mutts nuts and very accurate, as its capilliary theres no electrics involved so it works all the time Ive got two and they have been fine for years now.

This is the one, not cheap but for peace of mind priceless, http://www.ebay.co.uk/itm/TIM-52mm-...hash=item20fdea3f35:m:mMDByrtDiLASZGoVOXt-Hwg

The durite gauges are cheap and pretty accurate too. I bought 4 different stats (including a genuine waxstat) before I found one that opened at 88degrees. The good one was from eurocarparts