I would remove the lower radiator hose, drain, & refill with 50/50 MB coolant and clean tap water. There is a plug on the passenger side of the head that can be loosend and more coolant will come out of that.

A more complete way to do it would be to remove the upper and lower radiator hoses and thermostat and run a garden hose thru the entire system until clear water comes out. Remove hoses off the heater coil and run water thru that.

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Brian Toscano