As you face the engine, on the left side is the block heater. Just aft of that is the knock sensor. Just above that and hidden from sight is the magical drain plug for getting ALL the acidic fluid out, hopefully saving the gaskets from further deterioration.
I had a head gasket blow out once caused by the coolant changing from alkaline to acid by letting it go too long.

 

Nice good to know! Just replaced my rad with all aluminum and runs much cooler hardly can get the fan to turn on.

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