one of my engines are overheating. checked flow of water coming in, not as much on the other engine. i put a new water pump impeller in did'nt seem to help flow any. the other impeller looked fine. checked the thermostat in hot water to make sure it was opening, it worked fine. after checking everything i put it all back together and ran it in a barrel of water so as not to pressurize the system, it ran fine with no overheating, but i did'nt fix anything and now i don't trust it. when something is broken and you fix it thats good, but when you can't find anything wrong and you fix it then what is the answer.

Check to make sure that there are no restrictions all the way from the outdrive to the t-stat. Inspect the hose from the drive to the transom assembly to make sure there are no kinks (had this happen, lost a motor over it!) You may be fine when you are running in the driveway but once you put a load on the motor if you are not getting enough volume of water the temps will start to rise. If the hose appears to fine from the outside you may want to remove the drive and make sure that there is no restriction inside the hose! If everything appears clear you may want to install a water pressure gage to make sure you are getting enough pressure.