I have found this thread on gardenweb
http://ths.gardenweb.com/forums/load/cars/msg092255574892.html
they talk a little bit about it.
Here is a couple to the point:
"One of the products of combustion is water vapor, and some water vapor gets past the piston rings and into the motor oil, in the normal course of events. When a vehicle is started up and driven for an hour or more, the oil heats up, and the water evaporates. By installing a 180 degree thermostat, you have caused the engine to run cooler, and this will result in more water accumulating in your oil, if you do mainly short trips. If you ordinarily drive the vehicle for an hour or more, per trip, then there will be time for the water to evaporate, so there will be no problem."
"Raising the coolant temperature from 180 F to 195 F reduces emissios and inceases engine efficiency. However, I suspect that lubricity is better at 180 F with longer engine life. There is an argument that engine life may not be extended since the higher temperature tends to keep more moisture and condensates out of the oil.
The engine may not pass emissions tests when the coolant is too low. Regarding the oxygen sensor, most systems go into "closed loop" operation around coolant temp of 140 F, therefore, the oxygen sensor function should be operable at 180 F. Some systems may set a trouble code for "temperature too low". Some emission test stations scans the engine controller for certain trouble codes."
As far as i know computer goes in the closed loop based on the oxygen sensor data. WHen the engine starts first couple of minutes its in the open loop until first oxygen sensor gets to the working temp and gets out a small current of about 0.08v, then it goest into closed loop. I suppose some cars may duplicate this system with temp sensor but not ML. I tested it today with a computer. After about 2 minutes it went into closed mode. The temperature didnt even start raising.
I took out the thermostat today. Very simple, only two bolts, 30 minutes of work. You need to drain about a gallon of antifreeze so the level gets below the thermostat housing. The thermostat is removed from the housing with a simple twist. I dont know why the replacement comes with a new housing.
I am quite sure my thermostat is shot. I drove for 4 miles without the thermostat and the temperature was about 67. The temp outside was 62 at the time of testing.
I think i will drive without a thermostat for a while and see what happens. I will also track my milege and oil consumption.