Low temperature thermostat
 

Can someone with engineering background explain how "low temp thermostat" can lower engine temperature? My naive understanding is that the only reason thermostat exists is to speed up engine warm up period. Once operating temperature is reached, (90C?) it is controlled by cycling radiator fans (and grille shutters if equipped). Therefore any change in thermostat settings (going down 80C->71C->66C) must be augmented either by fooling coolant temperature sensor or by reprogramming DME. Otherwise it looks like pure oil snake.

I don't have an engineering degree but I have searched the forums recently prior to buying one. As I understand it, the low temperature thermostat opens up at a lower temp. The OEM thermostat waits until the engine is very hot prior to opening. There is an issue where the sensor is located monitoring the coolant's temp. As a result the coolant is actually hotter in other portions of the engine prior to the thermostat opening. Once the low temp thermostat is open the engine will run at the same temperature as it would with the stock one.

Hope this makes sense and I have interpreted my search correctly.

Actually, that is not completely correct. The thermostat in the engine functions exactly like the thermostat in your house, it sets the minimum temperature at which the cooling system will operate in a steady state condition (open road cruise). It does this by actually throttling the coolant flow to maintain the rated temperature.

On fully instrumented cars, the OEM 186F stat will have the car running at around 205-210F at cruise; the 160F stat will drop that temperature to the mid 170F range. Either will heat up when stuck in traffic, but the car with the 160F stat will cool back down after it gets moving again, while the OEM stat will go back to the 200's again.

The 160F stat is one of the cheapest positive addition's you can make to your car, followed by the larger oil cooler if the car did not come equipped with one.

Just found this:
Low Temp Thermostats: What’s the Advantage? | Tuner University
"The bottom line however is that in a street car, you’re increasing wear and getting no benefit. In a race car, it’s a band-aid but not one that you should plan to rely on."

Most of what he is talking about are simply idiotic and often wild claims about what a lower temp stat can do, which is fairly common, particularly amongst the "complex carbohydrate" boy racers.

The M96 engine has lots of restricted flow areas in the engine castings, which tend to get overly hot, much more so than the actual coolant temperatures. This is one reason these engines suffer cracks so easily when they are even slightly overheated. Secondly, UOA's run on cars before and after switching to the 160F stats show that the oil is also much happier in a cooler running engine, and a happy oil makes for a happy enigne.

There are no known downsides to running a 160F stat in these cars. We have installed a lot of them over the years, some on nearly new cars that now have over 100K, and in some cases nearly 200K miles on them, and they are all happy campers.

Thanks for clarifying! All my searching and reading and I knew I should have one... just missed the technical mark.