Johnson 50hp engines, like the one on the Mohawk...should they pump water our the exhaust ports that are right below the power-head all the time? Or is there a thermostat that needs to open? Reason I'm asking is that we ran her with muffs on the trailer and it wasn't pumping water. The broker wasn't sure if it just needed to warm up, if there was a problem with the muffs, or whether it might need an impeller. Also, any idea how hard it is to replace the impellor and reseal the lower unit?