Make sure the coolant is changed too, it doesn't last forever MB recommends changing it every 2 years, thats 24 months so you're due.

NOW PROMISE PROMISE PROMISE NEVER TO LET A COOLING ISSUE LINGER THIS LONG AGAIN.
I dunno where you got the idea this would be a $1500 repair, these cars aren't made of gold... New radiator, maybe a citric acid flush through the cooling system and you should be all set.

You don't want to run without a thermostat for 2 reasons:
#1. This is a diesel engine, if it doesn't get up to temp it won't run well. The engine relies on heat for compression ignition to work correctly.

#B. Your car will always overheat. Thats right and this is something folks used to American cars have a hard time handing, the thermostat opening closes off the loop back passage in the head, if the thermostat isn't present the coolant will take the path of least resistance and stay in the head. The thing that fakes some people out is that from a cold start the car will run fine for awhile but if you get it warm, shut it off and restart, it'll overheat... BTDT.

The thermostat is there for a reason, I hate it when people pull the thermostat rather than fixing the problem.

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Sadly Benz-less