99 s420 tempeture does not go above 80 degres celsius
 

i have 99 s420 drove in summer everything was fine but now winter time -20 to -30the temeture gauge does not go above 80 degress and the air from the heater is not really hot can anybody help thanx ahead

Welcome to the forum. I've never had my MBz in -20F weather, so I don't know how it would react to that, but if yours gets to 80C under those conditions, I'm not sure that's a problem. When it's "cold" here (45F), my running temp is just slightly over 80C. Check thermostat for too low operating temp. No cabin heat would lead me to check the duovalve first.

1999 / S 420 should be W140 model, is that correct?
You have to consider that Mercedes heating system is connected to the first circle of the car cooling system, this is one of the reason why they starting trowing heat very fast after the start of the car. If you driving very short distances the car doesn't have time to warm up.
What do you mean by: "air from the heater is not really hot"? Perhaps something is wrong with your temperature control unit?
Give a bit more info and someone could help.