I haven't had a bit of trouble with the 192-stat, in fact it really helped my mileage. I've run up hills, done full-throttle runs, idled in heavy traffic -- no problems whatsoever. Although...
I'd like to get some sort of baffle to keep air from moving over the radiator to get the temp up quicker in the cold weather -- I do a lot of Interstate/high-speed driving, so sometimes it takes a while to heat up. Cardboard is the easiest choice, but cheesy; plexiglas would look good but is expensive, harder to cut and could melt. I'm thinking of sheetmetal or a bra or something. I see big rigs and school busses with these padded-looking covers over the grill, so something like that or slip trim some sheetmetal and slip it in there.
I'm definitely sold on the hotter temps = better mileage theory.
that guy who is runing a 205F engine sounds like he is useing Propylene Glycol, a heat transfer fluid that I've used in solor hot water systems for in floor heat, it's nice stuff, slightly different propertys then etholyne glycol (the coolent you have now) he's claming to be useing a "water free" mix, not sure what's in that, but I know that the pure stuff we get 5 gallong buckts full of is so slipery that a pump can't pump it untill you ad some water, I used to have charts of how it was affected by heat, and how well it transfered heat, and Propylene Glycol seems like a good choice, not overtly better, other then it will not kill you if you or a pet drinks it, it's kind of sweet and a little bitter, they put it in ice cream, and cookies, and all kinds of foods.
my civic vx came stock with a 180F thermostat, a 192 is avalible, but wouldn't the car have been designed with the 192 if it was a good idea for mileage? it's a higher compresion engine, with lean burn so it's going to run hot at times i would think.
so why should I switch to a hotter thermostat? how much of a differnce will it make?
also, as far as smaller radiators, Geo's, civic 1.3, HF, VX, HX, all have half size radiators, from what I hear from people who race useing them, if they are kept clean there is no problem cooling under high loads, the half sized radiator is something like 14" wide, and 15" tall, the guy at NAPA was confused as to what would take such a small radiator.
my car came with a 195 thermostat but the problem was when I was driving around city my fans would turn on most of the time. I was told to buy a 1.2 bar radiator cap because it allowed the temps to be higher without overheating, or something like that.
After I bought the 1.2 bar cap my fans rarely turn on. They either turn on when I've been driving too long in traffic or when I'm racing for a prolonged period of time.
I noticed that my dad has a 1.1 bar radiator cap on his new accord and his fans rarely turn on too. Before the 1.2 cap I had a 0.9 cap which came with the car stock.
The radiator cap only controls the pressure in the cooling system - the higher the pressure the higher the boiling point of the coolant will be - unless you vent coolant it should not affect the fan turn on temp. There is a temp sensor in the radiator for turning on the fans - thermal switch. They could also be controlled by the computer but usually by the radiator so they will run when the engine is off if the radiator is hot enough. xB is running at 182-188 degrees - not hot enough to get the idle down to the desired 650rpm range ends up at 850 all the time wasting gas. Will have to tweek the stat opening temp and check the seals on the valve.