Sorry, I just can't resist. The self-contradiction and twisting in the wind is just to much to bear without comment.
Originally Posted By: azsynthetic
In the early day, the thermostat has two main purposes: to reduce engine warm up time and to provide heat to the cabin.
Oh, it was for more than that, right from day one. Its main purpose was to stabilize the engine operating temperature and remove the dependency on the surrounding air temperature and engine load that plagued air-cooled engines and engines without thermostats. Engineers realized early on that if they could design the whole engine to operate virtually all the time at an essentially constant temperature rather than varying by +=50 or 100 degrees depending on loading and ambient temperature, it would make their life far easier and make their product better. This allowed closing up piston-to-cylinder clearances, changing the alloys used, extending the life of the engine, reducing the complexity of fuel systems, and countless other things. That's one of the two fundamental reasons that liquid-cooled engines are utilized so much today: 1) liquid cooling allows higher power density- the engine package can be made small and have very, very high combustion chamber temperatures compared to an air-cooled engine because the heat can be quickly removed from the engine metal and rejected to the atomosphere by a remotely-located radiator, and 2) it can be made to run at a fixed, constant temperature by use of the thermostat, allowing a more optimized design. Air cooled engines can't come close- aircraft have all manner of cowl flaps and dampers on the oil coolers, but the engine metal temperature still varies more than a liquid cooled car engine does. It was quite the enabling little invention.
Originally Posted By: azsynthetic
Later on, its purpose includes: to "maintain" optimum running temperature
You keep recognizing that fact and then denying it! What your sentence above effectively says is: "the thermostat controls the engine temperature." "Maintain" equals "controls" in this context. That's what the rest of us have been saying for days. You can wrap yourself around a stupid axle by saying it "regulates coolant flow and nothing else" all you want, but why does it regulate coolant flow? To increase or decrease heat rejection with the ONE GOAL of holding the engine temperature as near constant as possible. Back to the core subject that started this thread- EVEN IF surfactants greatly improve the heat transfer out of the engine and into the coolant as well as out of the coolant and into the environment via the radiator... the thermostat will MAINTAIN the same coolant temperature either way. If heat flows into the coolant faster, the coolant will get hotter and the thermostat will open wider allowing it to go to the radiator and cool faster. If it cools faster in the radiator, then the t-stat will close a little to keep from over-cooling.
Originally Posted By: azsynthetic
(high engine efficiency) and for emission control (low engine efficiency).
Which is it? High efficiency or low? It can't be both. You're really stuck on this whole "emission controls reduce efficiency" bullfeathers that's been patently false since the early 1980s. Tell me- what are O2 sensors for? Emission contorol- YES. Does your car run better if you disable them? NO, they increase efficiency by providing feedback to the ECM so it can fine-tune the A/F ratio to the optimum stoichiometric value, which means the engine uses less fuel than if it just gets as close as it can in the blind, the way carburetors do. Does your car get better or worse mileage without a thermostat- WORSE because the quench zones inside the combustion chamber grow by a few microns, meaning that more fuel is left unburned on every firing of every cylinder. What about EGR- that's a "really bad" one right? Wrong. EGR on many engine designs dating back to at least 1984 (because I know a 1984 example) is used as a detonation controller much the way water injection works- the presence of CO and CO2 from recirculated exhaust in the A/F mix slows the burn rate and raises the effective octane of the A/F mix, allowing more efficient combustion without detonation.
Originally Posted By: azsynthetic
Since day one, the thermostat does all of this by regulating the flow of coolant and nothing else. Without a liquid cool system (coolant and radiator at the minimum), the engine thermostat has no purpose and therefore is useless.
What is the purpose of a light switch? To turn the light on and off, or to interrupt or allow the flow of electrons through a wire? What's the purpose of an oil pressure regulator valve on your engine's oil pump? To maintain a constant pressure in the oiling system, or to divert part of the oil flow back to the sump rather than to the engine? The light switch exists to turn the light on and off, it just happens to do it by interrupting electrons. The pressure valve exists to maintain a constant pressure in the oiling system, which it does by diverting oil back to the sump. A thermostat exists to control the engine temperature, which it does by regulating water flow.
Originally Posted By: azsynthetic
So, the question is how technical do you want to get?
You are not being technical. You are being pedantic, just as pedantic as saying a light switch doesn't turn the lights on and off. It just regulates the flow of electrons.