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195 degree ..... 18.00 MPG
175 degree ..... 17.91 MPG
155 degree ..... 17.82 MPG
135 degree ..... 17.74 MPG

For whatever it is worth
the above is what Kevin Gertgen's
'Fuel Economy Calculator' program

http://performancetrends.com/fuel_economy_calculator.htm

predicts for a
stock 1995 2wd 5.9 V8 46RH auto Ram pickup with 3.55 diff,
travelling down a level concrete highway at a steady 70 mph on a windless 42 degree F day

The program does not allow thermostat temps above 195,
but one might speculate that each
20 degrees of coolant temperature increase
might be worth
0.1 MPG

I know that if you idle a 1995 Ram for ten or so minutes
with the factory radiator fan removed,
but with Evans NPG coolant to prevent boil over,
the coolant temperature goes up from
193 to 240,
the idle smoothness noticeably improves,
and the fuel consumption drops from
0.66 gallons per hour to
0.60

When at speed on a highway,
if you raise the coolant temperature by blocking airflow through the radiator,
rather than by thermostat action,
you might get an even better MPG gain,
because air flowing through the front grille and then out the bottom of the vehicle is a major source of aerodynamic drag.

NASCAR teams of course routinely block off as much of the grille as cooling will allow,
and the new GM Cruze has shutters on its radiator opening.

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I posted that to show that the benefit of the higher MPG is small, but if people want to go after it, that is their choice, and many people like a challenge.

I would guess that rubbery parts
.... hoses, seals, vacuum lines
would have their service life shortened
by increased temperatures.

I would guess that aluminum to cast iron junctions,
like cylinder heads, manifolds
would be most likely to warp at higher tempertures.

I would not think that cast iron against cast iron parts would be affected much.

Since bore wall wear goes down with increased coolant temperature
(Continental Motors research)
I would guess that maybe piston ring wear would go down too.

Much of this bore, ring and piston wear
is from acids that are best kept as vapor,
never as a liquid (electrolyte allows corrosion)
so higher temperatures that are above the mixture's boiling temperature reduce corrosion.
Similar to 50/50 anti-freeze and sea water,
these mixtures of acids in water boil at temperatures above 212 F.

Continental Motors now mainly makes aircraft gasoline engines, and I for one was sad to see the press release last month where they were sold to a Chinese company.

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I posted that to show that the benefit of the higher MPG is small, but if people want to go after it, that is their choice, and many people like a challenge.

I would guess that rubbery parts
.... hoses, seals, vacuum lines
would have their service life shortened
by increased temperatures.

I would guess that aluminum to cast iron junctions,
like cylinder heads, manifolds
would be most likely to warp at higher tempertures.

I would not think that cast iron against cast iron parts would be affected much.

Since bore wall wear goes down with increased coolant temperature
(Continental Motors research)
I would guess that maybe piston ring wear would go down too.

Much of this bore, ring and piston wear
is from acids that are best kept as vapor,
never as a liquid (electrolyte allows corrosion)
so higher temperatures that are above the mixture's boiling temperature reduce corrosion.
Similar to 50/50 anti-freeze and sea water,
these mixtures of acids in water boil at temperatures above 212 F.

Continental Motors now mainly makes aircraft gasoline engines, and I for one was sad to see the press release last month where they were sold to a Chinese company.

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Not really sure how acids in the coolant effects the bore and rings. If you have coolant and coolant vapor in those locations your problems are a lot bigger. Generally, you're not "boiling off" anything as the system is normally maintained below boiling conditions. Finally, mineral acids have a higher boiling temperature than water, so if you boil an acid solution, the acid concentration in the remaining liquid likely remains the same or goes up. It would be type of acid specific.

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I posted that to show that the benefit of the higher MPG is small, but if people want to go after it, that is their choice, and many people like a challenge.

I would guess that rubbery parts
.... hoses, seals, vacuum lines
would have their service life shortened
by increased temperatures.

I would guess that aluminum to cast iron junctions,
like cylinder heads, manifolds
would be most likely to warp at higher tempertures.

I would not think that cast iron against cast iron parts would be affected much.

Since bore wall wear goes down with increased coolant temperature
(Continental Motors research)
I would guess that maybe piston ring wear would go down too.

Much of this bore, ring and piston wear
is from acids that are best kept as vapor,
never as a liquid (electrolyte allows corrosion)
so higher temperatures that are above the mixture's boiling temperature reduce corrosion.
Similar to 50/50 anti-freeze and sea water,
these mixtures of acids in water boil at temperatures above 212 F.

Continental Motors now mainly makes aircraft gasoline engines, and I for one was sad to see the press release last month where they were sold to a Chinese company.

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Not really sure how acids in the coolant effects the bore and rings. If you have coolant and coolant vapor in those locations your problems are a lot bigger. Generally, you're not "boiling off" anything as the system is normally maintained below boiling conditions. Finally, mineral acids have a higher boiling temperature than water, so if you boil an acid solution, the acid concentration in the remaining liquid likely remains the same or goes up. It would be type of acid specific.

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I'm assuming what he was talking about are the leftovers of combustion in the cylinders (water, unburned gas, etc...) that can form acids etc... that can cause wear on components and the need for the engine to reach a hot enough operating temperature so that those byproducts evaporate and cant cause any harm. I touched on that earlier in the thread.

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Combustion temp is like 1500 to 1800 degrees. Again, 20 degree difference in the t-stat won't make a measurable difference in these cars especially at the typical hot rodder oil change frequency.

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Typical hot rodder also runs their carbs to fat, and that will cause greater wear than their t-stat choice.

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