water temp
 

if I go down the freeway at 75mph them pull off and come to a stop
at the exit ramp the temp.gauge goes up, then as soon as i pull away
it drops again

auxillary cooling fan?
 

If you have one (or 2), probably not turning on.

water temp
 

It would definately be your auxillary fan. Have had a couple of MBs and have had the same problem. Check the aux. fan to make sure you're getting electrical to it. Otherwise is an easy replacement. you can get a new fan for 150.00, depending on model year, and install it yourself.

There is not necessarily a problem here. What is the temperature getting to when you pull off? The engine should heat up when you pull off the highway and come to a stop. If it gets to around a 100C and holds there, then I wouldn't worry about anything. If it keeps heating up and reaches 120C, then there is a problem.

Please post the temps that you are seeing on the gauge so that we may be of further assistance.

temp
 

it looks like 175-180 down the road,180+ when stopped. what temp does the fan come on. 300td 1979 do you know were the sending unit

Don't know sepcifically about your car, but most Mercedes that have a high speed based on coolant temp typically come on at around 230. Low speed is usually based on refrigerant temp in the A/C for dual speed fans. The mechanical fan clutch is set to engage at a lower temp.

If you are not getting much above 200, then it's not broken, it's functioning as designed.