CMCon98

The temp gauge should read about 85 degrees C; so 65-70 is to cold. Thermostats are available in different temps; I don't know what they will cost in US $, but can't be that much.
The climate controls with temp wheels for both sides of the car were used in almost all the MB types in Europe (for heater-only systems as well) and tend to break down once in a while...(electronic failure)
Start with the thermostat and see what it will bring you..

greetingz,

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1990 300SL-24
1993 C250D with a minor 600+k kilometer
www.MBenzNL.com(the Netherlands)