Did leak down test. Had an almost imperceptible drop in pressure. After more than a minute the pressure dropped less than half a pound. The kit I borrowed didn't have a direct fit adapter so I used the conical rubber one that gets press fit then expanded. Well it blew off the radiator and I had to spend 10 minutes cleaning up It looks like there may be a small leak from the thermostat. It was replaced about 7 months ago after it went bad and piddled on the floor.