1983 380SL is getting way too hot. Flushed with new thermostat this week. Runs about 100C going down the road but idling it shoots up to Red line.
Fan clutch seems to spin when hot with little resistance. Can can spin it about 1/2 spin with one hand when hot. Not sure what is the best way to determine if this is the problem.

One mechanic told me it was the Head gaskets but another told me that is not correct. Very confused and have been ripped off by the last mechanic so looking for my own solution.

Any help in troubleshooting would be greatly appreciated!