I believe the OP has a clogged radiator. Dexcool strikes again! The water is cold coming out of the radiator because it isn't flowing well and has more time to cool down. Use your IR thermometer to measure different quadrants of the radiator. I bet there's a significant difference from top to bottom.

If the previous owner had the radiator flushed, it's because it was clogged. But Disco Mike always said the radiators in these trucks can't truly be flushed because the passages are so small. So the flush may have helped a bit, but not enough to be a permanent fix. Unless the cooling system has been significantly modified, I don't think there's any way the system is 'overcooling'. I've driven in sub-freezing temps and the truck held steady at 183 (with a 180 stat). When the ambient temp gets into the 80s, the stock system will not maintain 180 in traffic, and very gradually creeps up to 205ish until I get on the highway and cool it back down. Others have reported similar behavior. So I would take 'overcooling' off the table.

Chubbs I think you have a similar problem, but just a year behind. Your symptoms are a combination of a cooling system that doesn't work all that well in the first place with a radiator that is clogging.

 

I've dealt with a handful of plugged radiators over the years. Normally that would be my go to explanation; but with this bypass system, it is just acting odd!

I drove it for about an hour straight today in 26 F ambient. Sensor/ECU said 197-203. Whenever I broke out the IR gun, EVERYWHERE else on engine side of the cooling system read 165-175. Including the steel outlet tube that feeds the top hose of the radiator/thermostat. That does not make sense whatsoever!! Thermostat housing is only 155-165 ish.

obviously its doing something because when I put the new thermostat in it dropped roughly 10 degrees across the board. Except for the radiator. Its still cool.

I've had systems that over cool. The race car in the picture below overcools with the fan on in cold weather. Had to really restrict the flow metering plate in the thermostat housing to get it to retain any sort of heat.

Im not quite sure if I am going to take the overcooling off the table quite yet. Mainly because when the ambient temps were higher, the truck actually ran a few degrees cooler.

Either way I hope to check the flow this week and if need be, I'll put in a new radiator.

Thanks for the input! I really appreciate it.

Just for fun, here is my Ultra4 that will be donating some of its spare parts to the Disco next summer.

 

It's normal in D2, to run cooler at ambiant temp between 60-75* compared to 30* & below the lower the ambiant temp gets, the radiator coolant temp will be lower & very cold coolant will close the thermostat very quickly, compared to a little warmer coolant flow, so with a little warmer coolant coming from radiator the stat will stay open much longer, & transfer more coolant to engine & ( a lot of let's say 150* coolant going to engine will drop temp more than just a little 110* coolant going in)
This isn't the case if ambiant temp is very high, like +90*,,
It has been reported that D2 with (standard 190* stat) have actually over heated in sub zero temp when idleing for long time, because at idle there is not enough pressure to force coolant from top holes in thermostat to open it,, (the top holes in stat are what trigger the stat to open to start the flow) but with a little higher RPM more flow with pressure & stat opens much sooner,,
But the fact that was mentioned about your radriator being partially clogged, is most likely the reason you don't get lower temps as you should,,
In 26* temps while driving you shouldn't get more than 192* temp at all,,

 

keep us posted. I would like to know what happens

 

See, I'm gonna have to disagree with everyone claiming the radiator is clogged.

Im running a 180 thermostat, with stock (replaced fan clutch) with a new radiator.
the thermostat has 20k miles on it, the fan clutch has 10k miles on it and the radiator has under 500 miles on it. And my truck has exhibited the exact same symptoms. While driving on the highway (over 40mph), i fluctuate between 188-190. Off ramps and downhill, it will either hold 188 or drop to 186. As soon as it comes to a stop, it shoots back up to 203-205 and SLOWLY comes back down to 194. Anything under 40mph, it hovers in the 194 range.
the only thing that i can think to replace would be the fan clutch, because over 40mph, it runs fine at 190. Under 40mph, its almost like the fan clutch cant keep up, but after a few minutes, at idle, it catches up.
And i know my rad isn't clogged because it brand spanking new. Nissens brand

Im beginning to lean towards eliminating the fan clutch and runan electric fan conversation and see where that takes me. just to find a suitable fan that i wont have to hack to make it work..

BTW, I have the ebay electric fan,

Land Rover Discovery 99 04 FFD Custom Electric Xtreme Cooling Fan Conversion Kit | eBay

Dont waste your money, it doesn't fit over the entire radiator. leaves a good 3 inches on wither side of the rad if you center the fan and leaves about 2 inches exposed on the bottom.
I contacted them, and they claim it needs room for extra airflow at highway speeds. yea, sure. someone tested it and it failed. Couldn't regulate the temperature.
End rant

Sorry to thread jack, but just my 2 cents.

 

over 40 mph your clutch fan isn't doing anything is it? at that point it's just relying on the airflow threw the grill isnt it?

 

yea, and over 40 mph, it cools just fine. no problems

 

Personally, yes. I believe out trucks run way too hot to begin with. I'm not happy seeing anything over 190*, i would rather sit in the 180's all day. i think a big part of our engine problems its the constant temperature swings. I think if you could stabilize them, enough to the point where we can sit in a very narrow temp range (for the sake of argument, say 180*-185*) all day long, we would be fine and see very few issues of cracked heads, blocks and moving liners.

Personally ,and i know I'm gonna get roasted for this but so be it, I also think the bypass system these trucks use for cooling is also poorly designed. Combine that with the fact that our trucks run rich and hot for the amount of power they put out, the system may have worked well from the factory, but add time and mileage the design shows it's flaws. If we could find a way to have a regular old thermostat right in the upper intake, instead of the hanging in space or in the upper hose(with the inline mod), I think we would all sleep much better at night, not worrying about the cooling system of our trucks, it is gonna hold today?

I say this as a Mercedes tech. trust me, Mercedes engineers make stupid decisions all the time and we have to fix them (as best as we can). Our cars (from the turbo diesel straight 4 all the way up to the 600 hp V12 AMG engines all have a simple thermostat somewhere in the engine, not hanging in space. and there thermal management is on point. Our 550 engines (M278 twin turbo V8) run at 1 temperature, All day. hot days, cold days, doesnt matter, 200*.
And they run at 200* to counteract the carbon buildup that happens with Direct injection engines.

I have very little formal training as an engineer. Not saying I'm the greatest technician that has walked the face of the planet, but being a technician teaches you alot.

Engineers roasted a $100 million dollar Mars orbiter through the upper atmostphere of the planet due to someone using the wrong measurements.

Let the flaming begin.

 

I have a brand new fan clutch so that probably isn't the cause. the only thing that isn't brand new on my cooling system is the radiator. Maybe its something to do with ambient air temp. 94-96 on highway and 203 when I stop in my parking spot.

 

Fair enough. I may have read your initial post incorrectly.
But I was an adventurer like you once....then i took an arrow to the knee....