The size of the overflow tank has nothing to do with how much coolant the system holds, just like the overflow tank on the engine coolant. I think it holds a gallon and a half, I don’t remember for sure though. They said they were having a hard time getting the tanks, probably because the company quit making them because they develop leaks because they’re a shit design. Like I said though I’m pretty sure the kit replaces both the lines which have AN fittings on one end.Wow that's not much coolant in the system and looks really cheap for $125.