Engine efficiency improvement through higher temp thermostat?
 

The hotter the engine the more effecient. I'm currently running water temps of 200-207. If I bumped that up to 215-220 and ran a high quaility coolant. What kind of bump in FE do you think? At what temp would the head gasket become a concern.

I can't answer the thermal stress question, but do have another one: will your engine let you run at higher temps? What's your electric fan's trigger temp?

Temp is a tricky issue because another effect of more heat is less timing advance (engine may be more likely to ping the hotter it gets).

I would have to tweak the fan. Right now it comes on at 213. From what I can tell from the scan gauge the timing is affect greatly by IAT but not so much by WT. I'm also thinking that this coolant, although pricey, might actually help in that regard and running it at 220- 225 would be the equivalent to the current 210.

Aren't you concerned about the increase in nox emissions from running hot?

No I don't think that there will be an increase in NOx. Increasing the engine operational temp is not like going into lean burn. The A/F would still be stoich(?) right ?

Well, the engine should lean out the mixture while running hot. Also, I have generally seen it stated that NOx increases on hot engines.

Instead of running your engine hotter, see if you could rig a cold-air intake for your induction system. An extension from the filter housing that runs right up to an opening (gasp!) in the grille or perhaps in a wheelwell, would permit a cooler, denser air charge. It's almost like having a very light-pressure, lagless supercharger.

If you do decide to run a hotter thermostat and hotter fan setting, consider running an auxiliary oil cooler. Again, you could put that someplace that doesn't require it be out in the wind, like flush with the belly pan (behind a screen for protection from stones) or tucked in a safe place inside a wheelwell.

I use a 203 degree thermostat, and Evans propylene/ethylene glycol coolant.

I gained 0.5 MPG by doing this. One of the few engine mods I've seen work.

Is that like a bicycle almost being like an Interceptor?

Actually I have done this with no affect on FE. Tested it up to 60 mph with no increase.