too much antifreeze - cooler running engine?
 

it's a$$-cold around here but i've noticed that my 97 E420 only gets up to about 70C no matter how long I drive. Car warms up fine, and blows hot air just fine.

I've considered a failing thermostat, but I realized that when I replaced the coolant 3 months ago, I used OEM MB coolant but ended up using a lot more coolant than distilled water. So the final mix ratio was more like 7:3 coolant:h2o rather than 5:5.

could the excess coolant keep the engine from reaching 80C?

no.the temp in cooling system is determined by thermostat and how much you use the heater.if you are extracting a lot of heat for the cabin it would tend to keep the engine a little cooler.70c is no big deal.

Antifreeze concentration does not effect expansion rate of spring in thermostat.

How are you doing??? Tick-tick still there???

I'm hope you have read my MENU#17 re mixture of af vs water?? It really shouldn't get above 50/50% and do any good for your car! Since, as you know, af does not help in cooling the engine, a mixture ratio of 70/30 is actually HARMFUL to your engine.

Normally you would expect it to run "WARM-to-HOT" in normal winter weather; it will NEVER run COOLER. So if you car is REALLY running at 70C, you should look into WHY it's doing that???

If you have a infrared thermometer that you can check to see if the IC temp gauge is really correct. I hope not since your MB should always attain 80C as a minimum. MB specs that temp (80C) as the minimum temp that insures the car meets specs. 70C is TOO low and will cause problems in the long run if it continues to run at that temp.

Tstat determines the minimum temp - if it is running at 70C then it is stuck open or not regulating appropriately.

In normal running, with enough cooling air over the radiator, the temp should rise to 82-85 C or so and stay pretty darn steady ...

Always a chance the gauge could be wrong, displaying 70C when it is actually 80ish ...