My case 590SL series2 circa 1991, is showing that it is overheating on the temp gauge. A while back the water temp sender stopped working and it overheated and blew out the cheap aftermarket plastic radiator that I had in it. Replaced the radiator with an all aluminum (still cheap but at least not plastic!) and replaced the sender. Found that the water pump was shot, which may have been the problem to start with, so that has been replaced. Now when I start it cold and run it for a few minutes, the gauge goes right to the red zone. The upper radiator hose feels warm, but not hot. Run it longer and the upper radiator hose gets hotter. The lower hose still feels cool. It acts like the thermostat isn't opening. Changed that out twice. What am I missing
Take the thermostat out, see if that helps. If that doesn't change anything, you could take the radiator cap off and run the engine to see if coolant is flowing. You could have some blockages in the engine block preventing coolant from making its loop.