About the tapping sound. We have had many 190Es come in with failing oil pumps. Watch your oil pressure gauge, make sure it is at 1.5 bar at normal operating temp idle, and rises to 3 bar upon acceleration. As far as the overheating goes, you'd better have the aux fan checked out, it may very well be locked up. If the problem persists after the fan is R&R'd, next try replacing the thermostat. However, usually when thermostats are near the end of their life span, they will tend to stick and cause the engine temp to rise to overheating then drop back down to normal. You might also want to replace the radiator pressure cap at this time. Next two items would be the water pump and radiator. I just put a radiator in a 450SLC that came in with the same type of symptoms as your car has, and that did the trick. But have the aux fan checked first and foremost!
'67 250SE Cabriolet
'93 300E 2.8