I just changed my thermostat to one that I purchased from my MB dealership, because I wanted exactly what was designed for the application......so I have an official MB thermostat, marked for 80 C.....

The thermostat is designed to open at 80 C to regulate the water entering the block for 80 C.....your temperature gages are reading a sensor in the cylinder head at approximately 90 C.....this is a normal 10 C temperature rise from water entering the block at 80 C and exiting at 90 C....

For those of you without an MB service manual.....there is a little arrow stamped on the edge of the MB thermostat.....this arrow points up.....

The thermostat that I removed was an AutoRad made in West Germany...had a slightly different construction and did not have an arrow.....

SB

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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG

Exactly. When the thermostat main valve is open, the temperature on the gauge should always be higher than the temperature at the themostat.

Tstat determines the MINIMUM termperature of the engine, given circumstances conducive (i.e. enough thermal transfer) - right?

Temp while at idle in traffic is determined by the ability of the thermal transfer system - coolant, two types of fans, radiator, etc - to deal with the extra heat - as they kick in the temp will never go back down below the set point. That said, I have had engines cool below the tstat set point on extremely long grades when the cooling effect was simply too great ... but, this was not excessive.

Maybe we should do a poll more formally, asking where everyone's needle points in normal operations - i.e. when tstat is determining minimum temp. Do it by specific engine type, and look for the most common position.

Both my previous 300CD and my current 350 SDL maintained temp so that needle pointed about one width above the 80C mark on the gauge.

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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg

that is where mine run. i cant remember what my 124 bodies did, it has been a good while since i had them.

when i first got the 350sdl it ran around 60. that is not good. i think it contributed to the sludging of the engine.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.