The short
Hex 4.5 tip or 1/4" socket wrench.No "radiator cap" -- use overflow tank.
~4 quarts in radiator a bit more in engine.
The long
I recently decided to change my own coolant to try to save myself the $80 that the mechanics charge. It looked like I had some residual oil in there from a blown gasket. It turned out that there was just some floating on the top of overflow reservoir, but I didn't figure that out until the coolant was coming out.
My first problem was to remove the old coolant. All the tutorials on changing coolant said to use a 1/4" socket wrench. I don't have a socket wrench. I looked at the plug, and I noticed that inside the 1/4" square hole, there is a hex hole. I have several hex wrench sets, and a ratcheting screwdriver with hex bits. I tried a few size, and the tip labeled H4.5 did the trick. I believe that is 4.5mm.
As far as I can tell the engine block doesn't have a coolant plug, so the only way to get the coolant out of the engine is to run it. I didn't actually have to do that part.
My second problem was to get coolant into the radiator. All the tutorials I read said to remove the radiator cap, and pour it in. Well, I don't have a "radiator cap". I think that many newer GM cars are the same way. The radiator gets filled directly through the overflow tank.
The car owners manual didn't state the coolant capacity, so I had to guess when buying. Now I have enough coolant for a long time sitting in the trunk of my car. The radiator/overflow tank holds about four quarts of liquid.
