So, if the fuel consumption comes from the mechanical fans turning as commanded by the thermostat....wouldn't the better choice be to go to electric fans rather than have the engine run at higher temps? There has to be a long (or maybe even medium) term trade off for running at higher temps for longer periods of time.
Fuel consumption from mechanical fan comes from two things, it's turning all the time, even when not needed. In my climate it's only needed when driving slow on hot summer days. The rest of the time, not needed.
The fuel consumption issue with a mechanical fan is that it's always cooling the engine to some extent, making it more difficult to get to full op temp on cold days, especially in Winter.
An electric fan only comes on when needed. This solving both of the problems with a mechanical fan. The electric fans in my Buick only come on on the hottest days of the year when driving slow. Same deal when I had an aftermarket electric fan in a Wrangler.
Also, an electric fan's temp sensor can be configured to make fan come on at the temp I choose. Thus offering more control over engine temps.
There is absolutely no risk to engine from running a 205F stat instead of a stock 195F stat. I did this for 6 years and 30K miles on a Wrangler with no problems at all. I have been doing this for 40K miles on my Buick with no problems at all.
The 205F Gates stat I like are really 208F stats, IME. They work great. The engine is more efficient and plugs, valves, and oil stays cleaner. Op temps are 208 to 210F, unless driving slowly uphill on a hot day, in which case temp gets to 215F and then electric fan turns on and temp drops back to 210F. Same for my LJ, XJ, and Buick.
That gives 2.5 to 3 mpg more. No downside at all.
The potentially risky stuff is what the hardcore hypermilers-economodders do, which is put the hottest thermostats made, like 215F, 217F, or maybe hotter than that if they can find them. Then their electric fans are configured to turn on at 5F to 10F hotter than stat. So they are running 215F to 220F for the more conservative economodders, or 220F to 225F for the more aggressive economodders. Combined with electric fans that gives great fuel economy, but may or may not harm engine over time. I'm not sure if it would harm the engine, but I'm afraid to find out.
My local Napa certified mechanic says engines can run at 230F all the time and not be harmed if they have good oil and a perfect cooling system that won't ever allow above 230F, BUT he says that it's not wise to run at 230F because there is no margin for error. He suggest running at 215F or less to be safe.
With my Gates 205F stat (really a 208F IME) I am running 208F to 210F most of the time. It occasionally gets to 215F (on a hot day driving slowly uphill) and then the stock electric fan comes on and quickly cools it down to 210F. That is perfectly safe and pretty darn good for fuel economy and having a clean engine.
Bottom Line of Temps:
If you want to try a little economodding on a Jeep 4L, start by getting a 205F Gates 33010 thermostat from RockAuto.com. It's safe and effective and works well with the XJ (or TJ) stock mechanical and electric fans (though it'd work even better with no mechanical fan). This is what I'm doing. I think my engine will last LONGER this way because it's cleaner.
If you want to be a hardcore economodder and are willing to take some potential risks, get a 215F stat, IMO. I wouldn't recommend hotter than 215F to anyone. If you do have a 215F stat, you'll need aftermarket electric fan(s) that are set to come on at 220F, IMO. After careful consideration, I'm not going this hardcore route, but there are economodders with Jeeps who are doing this with great success so far. I say "so far" because it remains to be seen if their engines will last.