whether one turns the plug or pulls the lower hose, the end result is the same. you only drain about 2/3 of the coolant out. The remainder is left inside the engine block. Pulling the lower hose is the method dealer uses. They don't bother to flush, just drain and refill. If one replaces his/her coolant regularly (i.e. every 2-3 year), this method is more than sufficient to keep the engine cool and rust free. If you have a large shallow bucket that holds about 3 gallon, pull the lower hose is the easiest and hassle free coolant change. you can always rinse the spill off with your garden hose.

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98 ML320 (gone but not forgotten)