Changing the thermostat on a W124 is a lot more work than on a W123. You don't have to drain the coolant first, but more coolant will come out because the thermostat is lower than on the W123. It's not something I'd want to do without a garage, especially in the winter.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL