Yes you are in fact only matching your stat to your colder climate, and this is the kind of information you should have relayed upfront before anything else. So in reality you have not increased your fuel mileage at all, you have just gotten your jeep to run at normal operating temps.
Somewhere way earlier in this thread I posted that a hotter stat
in my current Jeep, like two prior Jeeps, and in a Dodge car, and in my Buick, allows my engine to run same or similar temp in Winter as it already did in Summer with stock stat.
That imples I need the warmer stat to reach full op temp in Winter (and Fall and Spring). I didn't explicitly emphasize that I'm in a Northern climate, but my profile says WA, which is obviously a Northern state.
In hindsight a better way to say that would have been: A 205F stat allows me to run at full op temp year round (in a Northern climate).
The 205F stat is a huge benefit in cooler climates. Just as electric fans are a huge benefit in cooler climates. They are ideal in Winter here and OK in Summers here since we only see 90s occasinally, and only every few years see 100F. This Summer is cool enough (mid 60s to high 70s most days) that I need a 205F stat to reach full op temp even in Summer.
It was already widely known that elecric fans offer little (if any) benefit in a hot climate.
Now we have learned from you and Newtons that there is no gas mileage benefit from a 205F stat in a hot climate because your engine was already hot enough with stock stat. You didn't know that about your very hot climate until you tested it. How could I have known that when I've never lived in a hot climate? That's why we test things. Now we know.
You claim I didn't inform you this wouldn't help gas mileage in your hot climate. I didn't know. I only said it helped me, especially in Winter, and my profile clearly states I'm in WA State, an obviously Northern state.
I really only ever claimed the 205F stat helps my XJ and my other vehicles, which it has. Obviously in my climate. In hindsight, the climate part is important. The warmer stat and electric fan(s) mod is good for me in a Northern climate, and I think would be good for others in a Northern (cooler) climate. Those mods have never caused me any problems in 20 years doing them (in my Northern climate).
Now we know those two mods are NOT recommended for Southern (hot) climates.
Southern Jeep XJ and TJ hypermilers don't give up. There are many other mods in this thread that are suited for all climates, and a few mod specifically suited to hot climates.
However, another mod not suited to hot climates is blocking off part of the grill. Grill covers are only good for cool to cold climates (where they are good).
There has been some discussion on this thread about how the hotter engine temps might end up destroying your transmission, but there has been nothing said about your other components. I am pretty positive that the sustained hotter engine compartment temps caused the failure of my A/C system yesterday.
There is only one way I can see hotter engine temps reducing your gas mileage. Hotter might reduce gas mileage if engine constantly hot enough to keep your mech fan clutch fully engaged and your electric fan running often. I could see that might reduce gas mileage some.
I warned about this in an earlier post in thread where I said hotter is better to a point, but you don't want it hot enough to make your stock fans work harder.
My engine doesn't get hot enough (even in Summer) to make my electric fan come on more than 1 to 2 minutes per week (in Summer). I'm not sure if that's my 205F Gates stat possibly being slightly cooler than your 205F ACDelco stat, or if it's my heavy duty tow package radiator, or my tranny cooler, or my climate. Maybe all those. I posted earlier in thread that with stock fans I want the hottest stat that doesn't make the fans work harder (because if fans are working harder, they use energy, which burns gas).
So warmer is only more efficient if it's not constantly triggering mech fan clutch and electric fan sensor to come on. i.e. - warmer is more efficient to a point, but if it's triggering your fans to run hard all the time, it's to warm. I did say all that much earlier in the thread. Obviously climate is part of the equation, as has been called to our attention.
I'm sorry you're having problems with your AC. Since I seldom need to use my AC, I never put any wear and tear on the AC system. Also, my XJ never runs above 210F, except for occasional, brief 1 to 2 min visits to 215F during long slow 3 mph hill climbs on out hottest days here (80s).
So I am not qualified to comment on the AC. I would be interested to know what the repair people say about it. I read where Newtons said he thinks your AC problems are unrelated to your 205F stat. Newtons is a professional mechanic, race driver, and cudtomizer. He is knowledgeable.
I read where you said your brakes felt weak. I do not beleieve that could have anything to do with the 210F to 215F engine temps you've described. On a 96 XJ I used to own, for 1st year I owned it, it had a small one core radiator and a defective electric fan switch. With the stock 195F stat it ran 215F to 220F most Summer days, and 230F when off road in Summer. Engine was hot like that for an entire Summer (and we were having an unusual high 90s and 100+ heat wave for weeks that Summer) and it never hurt a thing in the engine or tranny or anything else, and my brakes were fine. I think you either got paranoid and imagined brake problems, or if you really do have brake problems, it is unrelated to 215F engine temp. IMO
Sorry about your AC, but Newtons said it's probably unrelated to 215F engine temp. In any case, hope it gets fixed and works out well.