Hopefully this information helps someone. On really hot days (90 +) our discovery would slowly creep up in temperature mostly on the highway with speeds above 45-50 and eventually would top 225. I could flip on the heat and run it at full blast which would bring the coolant temp back down into the 195-205 range. Having the A/C running brought the temp rise even faster.

What I checked:
1. The viscous fan turned about 1/4 turn by hand before stopping
2. The condenser fan kicked on at 212F (just replaced this earlier)
3. Coolant level was fine.
4. No leaves trash between the radiators and all shrouds/baffles in the proper places.
5. Coolant flowing in the overflow tank with engine turned on (although could not tell if it was moving as fast as it should)
6. Replaced the coolant cap.
7. No wobble from the water pump or leaking that I could see.

Turns out the radiator was clogged with silver colored mud (probably stop leaks) that the PO must have dumped in. There was a lot so probably multiple bottles.

Lessons learned.
1. Never use any kind of stop leaks product in your coolant system. Not that I ever did but this reaffirms not to.
2. Buy a UltraGuage or similar. My temp gauge never moved from the 3 oclock position and would have no idea this was happening expect for finding coolant coming out the overflow pipe.
3. Don't try to flush your discovery 2 radiator, doesn't work, fins/holes are too small at least when trying to flush out stop leaks crap.

Replaced the radiator with a Nissens and now my temps are now well within normal ranges with my softspring thermostat, in the 185-195 range around town and on the highway. Around 200-205 at idle.

 

Did you replace the radiator or just get the 180* thermostat?

 

Sorry, yes I did. Edited my original post to make that clearer.

 

What is a Nissens radiaor? Just as good as OEM?

 

Pertaining to number 2 on your list above:
AC Condenser fan should kick on when AC is switched On. It should be running Even when the key is turned to ignition #2 position (engine not running)

 

Nissens is a high quality radiator.

Condenser fans come on when AC is on AND certain conditions are met (speed and temp). Or at 212F.

180F stat is a great upgrade.

 

Where do you guys get this 180f stat??

 

Most of the Rover parts houses carry them. I can't remember the PN but it's been posted a number of times. I know I have a couple of times.

 

Rovers North is once source. Also, you can eval your radiator when truck is warmed up, engine off, measure temp top to bottom on fins with hand or IR thermometer. More than 10F cooler on bottom rows means they don't have as much flow due to partial clog, etc. I'd advise the real Rover part, not the MotoRad. One guy had multiple MotoRads bad. Also when you replace any major component like a radiator, or flush the system, the existing thermostat needs to be removed and top fitting washed out, there is a disc with small holes that can get clogged with trash.

 

FlyingZebra -You want LR part number PEL500110. It is the warm-weather "soft-spring" t-stat and is dark grey in color: Thermostat Housing Ds2 Frl 1 - Land Rover Part PEL500110

I bought mine from BP of Utah, though looks like they are backordered now: Land Rover Discovery 180F Thermostat PEL500110

You can also get a Motorad 180 degree stat, which is an off-white color and is part number 439-180.

Both are 180 degree stats, but my conclusion was that softer relief spring of the grey LR part allowed the stat to begin opening at a slightly lower temp.

Like others who switched I saw an 8-10 degree drop across the board.