You got it only half right, it has 2 functions.

1. To bring the engine up to optimum operating temperature as quickly as possible; and
2. To maintain the engine at optimum operating temperature thereafter.

The first.

To ensure that the engine reaches optimum operating temperature as quickly as possible, the thermostat restricts the flow of water from the engine to the radiator to virtually zero (a small flow is required so that the thermostat experiences changes to the water temperature as the engine warms up) until the engine reaches optimum temperature. The thermostat then opens up to allow coolant to flow through the radiator to prevent the temperature rising higher.

This mod only slows this process 10F to 20F will have almost no measurable effect on AF/Ratios when dealing with hot climates. If your car is running 20F over the stock T-stat your loosing power and increasing detonation in the motor.

The second part of what a T-stat does.

With the engine at optimum temperature, the thermostat controls the flow of coolant to the radiator so that the engine is maintained at optimum operating temperature, even as the power output, and therefore heat output, of the engine vary with varying load conditions.

Under peak load conditions, such as labouring slowly up a steep hill whilst heavily laden on a hot day, the thermostat will be approaching fully open because the engine will be producing maximum power, the velocity of air flow across the radiator is low, and the temperature differential between the radiator and the cooling air will be low. (The velocity of air flow across the radiator and the temperature difference between the radiator and the cooling air have a major effect on its ability to dissipate heat.) Note that even with the engine operating at full power, the thermostat should not be fully open, That's why you don't remove it from the vehicle.

Conversely, when cruising fast downhill on a motorway on a cold night on a light throttle, the thermostat will be nearly closed, because the engine is producing little power and the radiator is able to dissipate much more heat than the engine is producing. Allowing too much flow of coolant to the radiator would result in the engine being over cooled and operating at lower than optimum temperature. Again this is why you should not remove it.

The thermostat is therefore constantly moving throughout its range, increasing or decreasing flow of engine coolant to the radiator, in response to changes in power output due to vehicle operating load, speed, and external temperature, keeping the engine at its optimum operating temperature.

Do all vehicles need this, no. But if your running past 195F/90C especially sitting in traffic when there is little cool air flow over the radiator. (fans don't cool much with hot air flowing over them) Or if you have a heavy vehicle with a under-powered motor or hauling a heavy load. It can make a noticeable difference in engine performance especially getting rid of detonation in the engine which further kills power and increases exhaust gas temps.

As you have actually proved the point of this mod with your temp numbers.

On my Civic, with the halp of a ScanGauge, it shows that this temperature is between approx. 90-100°C. I've observed that the radiator fans starts turning at 101°C and stops at 94°C. With the A/C on, the temp can go as low as 92°C

Read more: http://tsikot.com/forums/engine-fuel...#ixzz1c7TCF7rc
Your hitting 101°C/213F and your only cooling down to 92°C/197F Your vehicle has a 195F/95C stat in it the most common OEM stat.

The optimum T-stat temp for tropical and desert temps is 82C to 85C.