Step back for a moment.

1. When driving you are 10 degrees above the stat temperature, and at idle going above 212 F.

2. Change has happened over several weeks or months.

3. It is not hot in Charlotte now or within 50 miles of South Tryon Street, and was a few weeks back.

4. You smell antifreeze and have slight coolant loss.

The suggestion about a water pump is a good one. As they fail, they will leak, increasing. They will also wobble the fan pulley as the bearing starts to go. The final failure is that the pump either siezes and throws off the belt, or the pump comes apart, fan and clutch turning at say 2000 rpm, and they head into the radiator and out the hood. You can remove the serpantine belt and turn the pulley by hand to check for any roughness, etc. You can also clean the area behind the pulley around the pump shaft, be sure it is dry, and run truck, then check again. If you can't reach behind there with a colored rag (shows up moisture better), use some paper towel. Moisture would show up on paper towel, even if you can't quite see back there. A poor water pump can lead to overheating, reduce the speed of the fan making it warmer at idle, etc. But you are on the young side for a water pump - however they can go at anytime.

You could have a head gasket leak into the coolant. More heat, which could account for temp rise, and more pressure, which could account for antifreeze being vented. There is a chemical test for combustion gas in coolant, like $35 and will do maybe 20 tests. This would be proof of HG problem, and you could use it again on other vehicles. You are also young for HG, but it is not unheard of.

You could also have garden variety thermostat, coolant level, and calcium build up in radiator, belt route issues, and trash between AC condenser and radiator, reducing air flow. Hopefully no DexCool. Loose hose clamp, bad hose, etc.

But something is making your Disco "hot to trot", BMW has those same bleed screws I think, and the thermostats can be had at major autoparts chains. It is too cool in Charlotte to be running 216 at idle in traffic.

Note: D1 and D2 use same water pump, so you can put the Mark 1 Palm Reader on each for comparison.

 

Forgot to mention - good idea to rotate water pump by hand while coolant pressure test underway, in case leak is only at a certain position. There are not many moving parts inside the cooling system.

 

the engine does not have to be running nor does the water pump have to be spun, that is the purpose of the weep hole in the water pump to allow water that has made it past the seal to drain. Preasurize the system to 20 pound and watch and wait, if you lose preasure you have a leak it's that simple. You should be wiggling all the hoses, radiator, heater, throttle body, verything you can lay your hand on while the system is under preasure, i have found many a leak under a hose clamp that had cut thru the hose.

 

Just like in construction, always a good idea to "shake the plumbing"

 

x2 to all the items mentioned above, but I would add to check your fan clutch too.

If the temps are near normal when moving, but climb when stopped, you could also be seeing a failing fan clutch contribute to the problem.

 

I received the new thermostat form British Atlantic. Drained the Dreadcool and filled with Prestone Flush and 2 gallons of distilled water. Bleed the system (and oh yeah, when you start the engine with the bleed screw left out.....you get a geyser). Drove her around the neighborhood and got her up to temperature. Let her cool down again. Drained her again. Change the thermostat and hose clamps and filled her up with Prestone and bleed her again. I hooked up the Ultra Gauge. Driving around the neighborhood I was getting 197F to 199F. Pulled over and let her idle a few minutes. Briefly touched 203 F and then back down to 199F. Drove around some more and the temp varied from 197F to 199F. Got on the highway and at 60 MPH she varied from 194F to 196F. Now this was all this evening and it was only 50F.

I will recheck/top off the fluid level tomorrow and pressure check the system again. I am glad I finally got the Dreadcool out. Blue seems to be running cooler and in a tighter range with the Prestone and new thermostat. I like the Ultra Gage. I feel much better seeing actual temps.

 

Good deal. I would suggest that you can begin to be too concerned about minor jiggles of the digital values, it certainly happened to me. I have learned to expect some overshoot on the initial warm up. Keep in mind that I see overshoot and the stat and coolant temp sensor are maybe an inch or two apart, would seem like in a D2 "plumbed by perverts" system the overshoot may be a little longer.

Would be interested if you could open up the old stat and post pictures from various points.