Start with thermostat. Also when you refill the cooling system make sure you end up with 50/50 or close to it. I helped take over a fleet of equipment where probably half of them were running straight coolant or close to it. Overheating was a common issue until we got the coolant mixtures straight.

I don't know if the cooling fan on an '83 240D has a clutch (my '77 does not), but if it does you might want to check it. I chased an overheating problem on a Lincoln Town Car for several weeks before I finally thought to check that, and it ended up being the problem (or most of the problem anyway). Also see if your electric fan comes on when it's supposed to.

If all that is good and it's still overheating, it's probably radiator time.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.