The drain plug for the coolant is located on the lower engine block in front of the starter.I think a 17 or 19mm hex plug. If you are going to flush the cooling system, you must first flush with a degreaser solution followed by a through rinse and then the citric acid flush. Don't worry about the citric acid harming your skin as S. Longston would have us believe that it will take your skin off. It's only strong lemonade. Follow the instructions in your shop manual.If you don't have the procedure,and you want them, let me know and I will be glad to send them to you.
By the way; if you do change from the green(Prestone)coolant and put Valvoline's Glysantin G 05 in you car,you should carry a spare radiator with you, because where the top radiator hose goes into the top of the radiator is going to break. I have seen three in the last nine months break, and all of them were using Glysantin G 05. I have been using Prestone for the last 34 years in Mercedes and have never any problems.
Bill Lewallen Lexington,Ky. Home of Valvoline Oil; but they have no production facilities here. No telling where their antifreeze is blended, since they do not make any ethylene glycol