I recently bought 560SL. Heater takes up to 30 minutes to heat up interior at 40*F outside temp. Temp gauge registers 85*C (185*F). Even when temp wheel is set on "Max", air blowing from vents is cool, maybe 75*F.

It acts like thermostat is stuck in open position. But gauge shows engine reaching normal operating temp after a couple of miles of normal driving.

Af first I thought this may just be the way MB climate control works. Thought I would seek some help for DIY repair.

Go buy a mono valve repair kit 000 835 06 44 replace it mono valve on 107 is at right side of engine near the fire wall unscrew four screws on top pull it out. don't do this when engine is hot(no pressure in coolant system)good lock.

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MB STARS Master Guild Technician,12 years MB tech
6 years independent shop owner

Did this on my 87 300SDL 3 weeks ago. Total repair time: 9 minutes. Results: everything works again. Examination of failed part showed that rubber diaphram had a microscopic crack that allowed coolant to cross it.