My 94 with 2.5 was running hot. It was running up to the red line. Changed the thermostat. Continued same old thing. Running Hot!. So I changed the water pump. No change in temperature. Maybe even running a little hotter. Wasn't any flow in the radiator when running with cap off. Changed thermostat again and temperature sending unit for gauge. No change. Was to the point I thought the head gasket was leaking ...even though there wasn't water in the oil. I decided to try to take thermostat out and run it to see what would happen? Temp was running low temps. Could see flow in radiator. About 185. Took the two thermostats and threw them in a pot and boiled them. They both opened. Now I am almost positive the head gasket was leaking. Remembered reading about vapor lock and the air pocket around thermostat not letting it open. Decided as a last ditch effort to drill a 1/8th inch whole in the thermostat rim. Put it back together and the old girl ran 210•. Took it out and ran it hard. Barely moved above 210•. Fixed! A simple hole in the rim of the thermostat saved me from tearing the head off and replacing gasket. You would think that if this is a usual problem on YJ's when replacing thermostat they would put weep holes in them. Ugh!!! Just glad it wasn't more serious. Hope this helps someone else out there when replacing the thermostat.