One other thing to consider, and often overlooked, is that if you use a coolant mixture of more than 55% antifreeze it can cause your engine to run hotter than normal.

Antifreeze DOES NOT dissipate heat very well. Check your coolant mixture.

Here is a Quote from Mercedes"

"Concentration
50% anti-freeze/corrosion inhibitor offers protection against freezing down to approx. -37°C. A higher concentration is only practical when the ambient temperatures are lower.
A 55% concentration of anti-freeze/corrosion inhibitor offers protection against freezing down to approx. -45°C.
More than 55% concentration of anti-freeze/corrosion inhibitor reduces the protection against freezing and has a negative effect on the heat transfer."

Phil

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'95 E300 Diesel, 264,000 Miles. [Sold it]