Reply to "Radiator cap TOP gasket leak, pressure"

Angelo, you may have a few problems. First, brass radiators balloon the water tubes in the core somewhere around that pressure, closing off air flow thru the radiator. This can happen as the cap's pressure relief is not designed to flow much volume, only small amounts. We usually recommend no more than a 16-lb cap. Welded all-aluminum radiators (no epoxy to seal tubes) will handle a little more pressure- maybe up to 25 psi intermittently, but only NASCAR uses 22 psi (or higher) caps- and that's only because they don't have rad-fans at all, so their pit stops are always engine-heaters.
Second, the cap or tank neck top may be distorting and leaking under that much pressure, or the cap may have been defective out of the box. Cap-tabs are easily bent with a pliers if the sealing pressure needs to be adjusted. Finally, I've seen leaks from the weld or whatever fastens the small overflow tube to the tank neck. Leaks there are often hard to see and are sometimes mistaken for cap leaks. As Julian said, we ARE talking about the small surge tank, not the larger overflow tank, right? The big overflow tank is only supposed to have a cap with a splash-guard gasket, not a pressure cap.

For everyone: it's good to eliminate even small rad-cap leaks; water from the cap on a surge tank in the stock location runs down the tank, down the inner fender and right into an oval hole cut into the lower right subframe's top. So if the car's frame rails haven't been drilled on the bottom for the recommended 4 per side drain holes, the frame fills with water and rusts! Some cars will hold water for weeks after a short drive in a surprise rainstorm.