I had a bad reservoir. The dealer tested it for me and it held pressure just fine. My problem was the overflow side of the tank was leaking so when coolant would be pushed over there it would leak out and there would be nothing to go back to the pressure side when the truck cooled off. I bought a Wherli tank and the problem was solved and it looked damn good. Lol. Replace the tank. You can find them online for about 150.00.