Radiator/coolant system problems have plagued me more than any other, so I have learned a thing or two along the way.

I'll probably get some flak for suggesting this, but reduce the coolant mixture to, say, 5% (or less) coolant to 95%+ water. Nothing absorbs heat more effectively than water. Anything mixed with it simply reduces its heat absorbing capability.

I have been doing this for the past two years and, in 90+ degree summer weather, I run at 80 to 82 on the highway and about 90 in stop and go traffic. I don't generally go over 90 to 95 unless I am idling in traffic jams.

Also, make sure your cooling system is airtight. The tiniest leak will lower pressure and decrease cooling capacity.

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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black