I purchased this 1991 350 SDL and had the rad and thermostat replaced due to leaks. I have never owned a MBZ before this, it seems that the temp gage shows the engine running hotter than seems normal. During regular driving including freeway, the temp gage is up near the final line at 120c. Sometimes it is lower at the next mark down or between the two. At what temp should the gage show? Is this not running hot? Please advise.