I'll throw in my 2 cents. Others may agree; others will differ.

I would flush the radiator out with a garden hose first before installing on the car. This is likely a waste of time, but that's just something I would do.

Next install the radiator and hook up the hoses. Remove the thermostat housing and remove thermostat. Reinstall thermostat cover and gasket. You do not have to tighten it back down real snug. On the passenger side of the engine block towards the back is a 19mm engine block drain plug. Attach a length of heater hose and loosen the plug and allow coolant to drain into a pan. Pour the old coolant in gal. plastic bottles of some kind.

Now place a garden hose in your coolant recovery tank after removing the pressue cap. Leaving the engine block drain plug open, turn on the hose and let her flush for several mins.

You may be able to get the radiator drain plug out and then you may have a hard time getting to it. In my case it's in a strange place, so I always end up pulling a hose off the bottom of the radiator to drain it.

You can use your imagination and fwd flush/back flush a number of ways.

When all of the garden hose flushing is done, I would reinstall thermostat, pressure cap, etc. and ensure system is full of the tap water you''ve been using and go drive the car for 15-20 miles. Return, allow to cool, drain and flush again. Do this a couple of times.

You are not going to damage or corrode the system using "tap water" for a couple of short runs. Driving the car 'til warm with just tap water will help break loose and clean the system.

When you're done you can install a mix of MB coolant and distilled water. Some say to use a 50/50 mix, some say 60-water/40-coolant, some say 70-water/30-coolant. It's your call. Coolant does not dissipate heat well.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"