You are way too hot, my friend. Check out PMIs comments but please verify your sending unit is accurate before you spend too much, or tear down the water pump. When mine gets HOT HOT its at 210 or so, then I need to pull over and let her rest. That has only happened 2-3 times in three years. If I saw my gauge get anywhere near 240 I'd have a heart attack. For grins, try a 165-170 thermostat.