I rarely drive for very long in my Disco, its mostly a rainy day/winter car, commuting to work is a 20 minute a day round trip, and even less for trips to the store etc... but I was on the highway this weekend for about 3 hours duration going on a trip (195ish F all day long on the highway). Normally my idle/slow traffic temps are about 210-215 max, high speed fans kick in and it never goes above that.... been that way for over 3 years so...

Anywho, on my way home I noticed after getting off the highway my temps creaped upto 230 F and stayed there at a traffic light, dropping back only after I started moving again (wasnt a particularly long light either). When I got home, I took my IR thermo (it was at 215 F when I turned it off at home which is the normal high temp idling etc) and got some strange readings. The thermo only registered 85ish +/- 2 degrees F at the top of the radiator, and about 6-8 inches below that (the farthest down I could angle the thermo through the front grill) at 75ish F. I was tired and only had a few momments to tinker around, but i intend to look at it again after work, let it idle in the driveway and IR temp map the radiator better, and maybe a few other spots. Driving to work today the temps looks normal, never exceeding the 210-215 range.

(ps. i have a 180 thermo and plan on getting a new radiator anyway, just rough with money now)

 

Try to repeat your test warmed up, but on the back side of the radiator. Sounds like radiator is clogged on the bottom or higher. $200 Nissens at Rock Auto. Is the 180 stat a Land Rover one? And the fan clutch couild be wimpy, when warmed up give it a spin and release, should stop is less than one revolution.