If you drove for 10+ minutes and the coolant never got past 60, I think you have your answer. New thermostat time. It likely isn't stuck fully open, but certainly enough for the engine not to warm up. Low heat is only one of the problems. A cold engine will kill your power and economy and fail to drive moisture out of the lubricating oil.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]