I have a recovery tank mounted down by my motor mount on my 250, fluid comes in the top through a tube that reaches the bottom of the tank, the over flow tube is just inside the tank and dumps on the ground if the tank ever fills up all the way. I used a 12" piece of 3" exhaust pipe, some 3/8" brake line. and some sheet metal caps. Its all welded together so I can't really see how much is in it, as long as it doesn't dump any out I'm happy. I do check the radiator every now and then. I don't believe it matters where you mount the overflow, thermo expansion and contraction should move fluid where it needs to go, though most are mounted level or just below the top tank. Our 2026 school buses have the tanks above the radiators, Ford trucks are level with the tops, and most of the commercial mowers we have are close to level with the top radiator tank.
