I'll jump in with my accumulation of prejudices on this subject ............
In engines Oil, Coolant and Fuel are it's lifeblood's and so should have
first priority.
Oil needs to be kept below that temperature where it breaks down. Better
oils break down at higher temperatures and oil coolers help prevent this
being a problem even with lesser oils.
Coolant needs be kept below that temperature where it boils. Increasing
coolant pressure increases the boiling point.
Fuel quality, spark advance, compression ratio, fuel to air ratio, and
combustion chamber design among some other things affect ping
characteristics. Hot engines are more prone to ping, especially engines
with combustion chamber deposits left over from using leaded fuel.
If you keep all the above mentioned items under control, the hotter an
engine runs the better the efficiency until you reach such a high
temperature that you have metallurgy problems.
Air cooled piston aircraft engines usually have a Head Temperature operating
range from 200 to 500 degrees F. Oil temperature red line is 245 degrees
F. Nothing sophisticated here as this technology dates from the 1930's and
that Five Hundred Degree Head Temperature is not a typo.
With higher temperatures efficiency improves, Miles Per Gallon improves,
and there is less pollution.
A 15% decrease in your fuel mileage due to the 165 F thermostat astonishes
me. I have no real basis for what to expect but would have thought maybe a
few percent. Perhaps other factors are involved ?
Ricardo's tome or similar would discuss the theoretical difference.
Don
From: RickStapls
Date: Saturday, August 01, 1998 07:15
Subject: Re: GMC: Thermostat temps
>
>> What else is the lower thermo costing me?
>
>Jump in!
>>
>Here we go again! Which is better, blondes or redheads? It seems
everyone
>has an opinion on thermostats, passionately defended. (For the record, I
>prefer redheads, but they're rare.)
>
> Let's try some logic here: It is natural that your operating temp will
>read lower with a 165 F thermostat than with a 195, as that is the
>thermostat's job: to allow the engine to reach its rated temp, then
maintain
>that temp if possible. Please note that until that temp is reached (and
the
>thermostat opens) either or any thermostat will perform the same. ie: it
>won't warm up any FASTER with a 195 F than with a 180 or 165, just will
>continue to warm up a little longer and hotter.
>
> As someone noted, higher temp thermostats were introduced partly for
>emissions reasons: to reduce the quench effect on the combustion flame
front
>in those nooks and crannies our older engines are fraught with. At the
same
>time, however, they do help improve gas mileage a little, both through
>improved combustion as noted, and thermodynamically (slightly less of the
>combustion heat is absorbed by the engine block and heads if they can be
>maintained at higher temp). Improved oils and coolants help make this
>increased temp sustainable.
>
> Please don't confuse supplying cooler (hence denser) air to the
induction
>system, thus increasing power, with running the cooling system at a lower
>temp., which has little or no affect on power. The only power advantage of
>lower operating temp. is that it allows you to advance the timing SLIGHTLY
>without inducing ping, IF you have a problem with hot spots causing
>preignition otherwise. (But none of us would do this anyways, risking our
>pistons and producing gross pollution out the tailpipe, would we??) The
only
>dependability advantage is that by maintaining the block and coolant at a
>lower temp they can absorb a little more heat in case of pump/fan/radiator
>failure or overload. (IMHO you should fix the problem with your cooling
>system rather that put in a colder thermostat.)
>
> I recommend the 195 degree in most cases. YMMV.
>
>Rick Staples
>
In engines Oil, Coolant and Fuel are it's lifeblood's and so should have
first priority.
Oil needs to be kept below that temperature where it breaks down. Better
oils break down at higher temperatures and oil coolers help prevent this
being a problem even with lesser oils.
Coolant needs be kept below that temperature where it boils. Increasing
coolant pressure increases the boiling point.
Fuel quality, spark advance, compression ratio, fuel to air ratio, and
combustion chamber design among some other things affect ping
characteristics. Hot engines are more prone to ping, especially engines
with combustion chamber deposits left over from using leaded fuel.
If you keep all the above mentioned items under control, the hotter an
engine runs the better the efficiency until you reach such a high
temperature that you have metallurgy problems.
Air cooled piston aircraft engines usually have a Head Temperature operating
range from 200 to 500 degrees F. Oil temperature red line is 245 degrees
F. Nothing sophisticated here as this technology dates from the 1930's and
that Five Hundred Degree Head Temperature is not a typo.
With higher temperatures efficiency improves, Miles Per Gallon improves,
and there is less pollution.
A 15% decrease in your fuel mileage due to the 165 F thermostat astonishes
me. I have no real basis for what to expect but would have thought maybe a
few percent. Perhaps other factors are involved ?
Ricardo's tome or similar would discuss the theoretical difference.
Don
From: RickStapls
Date: Saturday, August 01, 1998 07:15
Subject: Re: GMC: Thermostat temps
>
>> What else is the lower thermo costing me?
>
>Jump in!
>>
>Here we go again! Which is better, blondes or redheads? It seems
everyone
>has an opinion on thermostats, passionately defended. (For the record, I
>prefer redheads, but they're rare.)
>
> Let's try some logic here: It is natural that your operating temp will
>read lower with a 165 F thermostat than with a 195, as that is the
>thermostat's job: to allow the engine to reach its rated temp, then
maintain
>that temp if possible. Please note that until that temp is reached (and
the
>thermostat opens) either or any thermostat will perform the same. ie: it
>won't warm up any FASTER with a 195 F than with a 180 or 165, just will
>continue to warm up a little longer and hotter.
>
> As someone noted, higher temp thermostats were introduced partly for
>emissions reasons: to reduce the quench effect on the combustion flame
front
>in those nooks and crannies our older engines are fraught with. At the
same
>time, however, they do help improve gas mileage a little, both through
>improved combustion as noted, and thermodynamically (slightly less of the
>combustion heat is absorbed by the engine block and heads if they can be
>maintained at higher temp). Improved oils and coolants help make this
>increased temp sustainable.
>
> Please don't confuse supplying cooler (hence denser) air to the
induction
>system, thus increasing power, with running the cooling system at a lower
>temp., which has little or no affect on power. The only power advantage of
>lower operating temp. is that it allows you to advance the timing SLIGHTLY
>without inducing ping, IF you have a problem with hot spots causing
>preignition otherwise. (But none of us would do this anyways, risking our
>pistons and producing gross pollution out the tailpipe, would we??) The
only
>dependability advantage is that by maintaining the block and coolant at a
>lower temp they can absorb a little more heat in case of pump/fan/radiator
>failure or overload. (IMHO you should fix the problem with your cooling
>system rather that put in a colder thermostat.)
>
> I recommend the 195 degree in most cases. YMMV.
>
>Rick Staples
>
