PEH,

The point is if there is no thermostat in an MB system, too little water will make the trip through the radiator and too much water will go through the bypass port. Leading to higher operating temperatures.

It is also true that for a given set of circumstances, such as flow path resistance, flow path length, air temperature and air flow, the outlet water temperature from the radiator will vary with water flow assuming a constant inlet temperature to the radiator. In general it will vary in proportion to flow, with higher flow rates yielding higher water temperatures. Lower flow rates will yield lower temperatures as the same inlet temperature, and the same differential temperature between the air and the inlet coolant flow temperature condition would exist for both cases. So the longer the water spends in the radiator being cooled the more heat it loses and the lower its temperature gets.

Sending more hot water into the radiator will increase the efficiency of the radiator and may reject more heat to the air, which I believe is PEH's point. But it may not achieve the balance of by-pass flow at a given temperature mixing with water cooled by the radiator that the system expects at a given coolant temperature in the thermostat housing. Especially if there is no thermostat in the housing.

The MB system is designed to throttle flow to the radiator and through the bypass line at nearly all conditions except full throttle, on a hot day, with max load going up a very long hill. If this condition exists where you live all the time, well, you might be best off with a plate welded over the bypass line since you probably don't need heat often and can live with cooler engine coolant for longer during start ups. You also probably don't need to worry about -20*F water being injected into the engine when the thermostat cracks open with the engine near normal operating temperature in the dead of winter.

If you live in places with temperatures in the range of what exists in Germany, with summer trips to Italy and Greece and Spain, which is common, you should leave the thermostat in, and if there is an overheating problem, you should try to find and fix the problem. Removing the thermostat won't solve that problem.

I read here by someone recently that the thermostat seat in the thermostat housing can become corroded and leak enough to prevent shutting off the by-pass port, giving a similar result - too much flow through the by pass port and not enough flow through the radiatior leading to overheating. Changing the thermostat won't help in that case. I have noticed the seat in my old 240D is pretty chewed up and if I keep the car for much longer I will see what a new thermostat housing costs and test the idea as my 240D runs hotter than it used to run by about 10*C. Flushing, changing sensors and so on has not helped. Neither did a new, boiled and verified thermostat. So, that leaves the housing. Maybe I'll JB Weld the seat to build it back to a solid sealing area and see how that does first.

Hope this helps. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)