I'm riding the inline thermostat high right now. So I would do that and you'll run 188 all the time.

But first make sure they bled the air right. And if you want to try and genuine 180 thermostat.

Disconnect coolant tank carefully when engine cold (don't break anything) and put on top of battrey box or hold it high, (make sure it won't move around if start engine,) fill a little over full line, then loosen bleed screw on T and let it lose coolant till see study stream of coolant, then tighten , (don't over tighten it, or you will break it),
Then start it , let idle a little, now sit inside, and give it little gas , then release pedal, if you hear water fall sound means there is air in heater core, if so, best way to get it out is to park the truck somehow that front of truck is at least a foot higher than back , youCan use ramps under front tires, or find a high curb (and using low gears drive front tires on top of curb),

Put coolant cap back on & tighten, let engine run till hot ,while giving gas now & then till gets hot, then turn off & let it cool down, if you repeat a couple times , and front of truck is raised enough , should get red of all air in heater core , (no more waterfall sound from under dash), and it should run normal temp even with standard thermostat,

Of course lower temp 180 t-stat will bring temp down another few degrees,
Good luck,

Crank the temp all the way up on your AC head unit and find out if the system will blow hot air, i.e. "The heater." This will give you a reference point of air in the coolant system. If it is blowing cold air then you definitely need to bleed the air out of the cooling system. And definitely heed the advice of replacing that OEM Tstat with a soft-spring 180 deg. If the shop used red dex-cool for coolant then you will want to flush that out and use the traditional green fluid with distilled water and a coolant additive. Do all of this yourself so that you know exactly what's going into your vehicle and finally bleed it properly. As long as you have a screwdriver and your OBD or outboard temp Guage you will have no problem. My temp was about 217 also. I did everything mentioned above while replacing fan and clutch and my temps went down 20 degrees. Good luck and get that under control STAT.

Can you explain that, please ?

If a cap does not hold pressure; would that cause overheating ? Or just cause coolant/steam loss and because of that loss, could overheat from lack of coolant ?

Am sure without a cap will not overheat. It will not pass 100C / 212F.
But we have to define a temperature borderline to name it overheat.

I propose defining overheating as over 110C / 230F --->Would that be reasonable ? Is there an already established consensus ?
New cars with idiot pointers tell us nothing, as what is factory 'normal'
If I remember well, the top 'white zone' on Land Rover is 111C

Water under pressure boils at a higher temperature that water not under pressure.

"When the external pressure is:

- less than one atmosphere, the boiling point of the liquid is lower than its normal boiling point.

- equal to one atmosphere, the boiling point of a liquid is called the normal boiling point.

- greater than one atmosphere, the boiling point of the liquid is greater than its normal boiling point."

And yes, it would keep steam from escaping as well...

We all know fifth grade boiling points.

It is about overheating; which is not the same.

Well if it's such common knowledge to even a 5th grader then why are you asking those '5th grader' questions questions in the post previous to my last? Most people don't get snarky when people offer them helpful advice and suggestions. I'm sorry you're having a bad day.

Put in the 180 degree thermostat now.
If you don't do that - you are absolutely asking for trouble.
This is the middle of the summer.

Just do this.
Don't question it. Do it.

Made the BIGGEST DIFFERENCE on my D2.
You will drop 10 to 20 degrees.

If you refuse this advice - you deserve to overheat. Sorry but... that's the truth.

Drowssap and June8200 are correct. Everything has to be leak-proof and air-tight for a pressurized cooling system, such as that of the Discovery to work properly. I had a tiny pin-hole crack in the neck of my expansion tank which is the same thing as a faulty cap in this case. Even though the loss of coolant was so unremarkable that I could not even find the source of the leak without having to pressure test, my vehicle began running hotter and would have over-heated had I not known there was a problem.

Updated Information
 

Hello all,

I was mistaken regarding the thermostat, it is not an OEM, but the NAPA 180 degree thermostat. The part number is NBH 34723. Since this is a 180 degree thermostat, should I still purchase the Land Rover 180 degree thermostat that was recommended in this thread?