Did anyone notice that he's worried about the temp gauge going above 80 degrees? His t-stat isn't even starting to open up at 80 degrees. It starts to open at about 87 degrees, and isn't even in the full open position until 102 degrees.

People usually get scared when the gauge goes above 100 degrees, but 80 degrees would be considered very cold for this engine, and if it's running at or below 80, you're car is probably running rich as a result.

I believe you have an 87 degree thermostat, and that is the temp that your t-stat starts to open. I'm sure your car should be running between 87 and 92 degrees most of the time, and will probably run about 100 degrees at an idle in hot weather. Here is what the CD says about the cooling system and temperatures on M104 engines:

Thermostat will start opening at 85 to 89
Thermostat will fully open at 102
Viscous fan clutch will cut-in at 96 to 104
Viscous fan safety cut-off will ocurr at engine rpm 4500
The same will ocurr at fan rpm 3250
Electronic fan (1st stage) will cut in at 16 bars of refrigerant pressure)
Electronic fan (1st stage) will cut out at 11 bars
Electronic fan (2nd stage) will cut-in at 107
Electronic fan (2nd stage) will cut-out at 100
A/C will go into 50%on, 50%off cycle (20 seconds interval) at coolant temp 121 to 123
A/C will go into emergency shut-off mode at 126 to 128
Pressure cap will open at bar 1.3 to 1.5
Coolant temp max is 130

Remember that water boils at 100 degrees celsius, but with a 50 / 50 mixture of water to coolant, your boiling point is raised to 120 degrees, and the car isn't considered to be overheating until the temp exceeds 130 degrees.

MB designed these cars to run hot, and 100 degrees is not even considered close to being hot.

Now, many of us on this forum (including me) doubt the wisdom of the brilliant German engineers for these cars, and carry out modifications to prevent the car from going much over 100 degrees.

I have installed the "cool harness" that JimF sells, and it causes the high speed auxillary fan to engage at 100 degrees, and runs until the temp reaches 82 degrees.

But I think something is wrong if your car runs below 80 degrees. Maybe your t-stat has been stuck in the open position and you aren't aware of it.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".