I have a 95 E320 with the same issue. However, I did replace the thermostat and still have the issue. The temp gets up to normal operating temp, and the aux. water pump does work. What could be my issue? It blows only luke warm at idle and at highway speed.

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93 300D 2.5 Turbo, Black/Palomino 273K
09 E350 Black/Black 41K

was it the thermostat or was it low on fluid?

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1994 C280
2009 VW Tiguan
1993 Toyota X-tra Cab SE-5


1973 220D ... Gone, but not forgotten
1991 Alfa Romeo 164L Gone, wife MADE me forget it

2006 Hyundai Tucson... just straight out FORGOTTEN!