Hi, it sounds like you may have a fault with one of the temperature sensors in the climate control system is unable to regulate the temperature. When you dial the temperature to maximum it overrides the sensors. I would suggest that you have the car connected to the Mercedes Star Diagnosis tester to read out the fault memory of the system and to check the actual values of the sensor. Most likely you will find a sensor giving an illogical reading.
will a regular obd scanner find the code and what's up with the marked rise in engine temp related?
No, you will need a factory level tool that can read faults and actual values in the climate control system. Is the temperature running hot all of the time or only at idle?
all the time but it started at the same time as the loss of heat
I'd first check the coolant level and then replace the engine thermostat.
okay, level already check and full, heater worked fine this am and temp was normal, seems more than a coincidence that both started at once; where do I have to go to find that level/type of tester
Any Mercedes specialist will have a factory level scan tool.
Either the dealer or an independent who specializes in Mercedes repairs.
thanks, XXXXX XXXXX u would say that have done all my own work since my 59 190sl but the newer cars control systems are a bit beyond me now [back to my 67 AH 3000]