Yamaha 4 stroke 4 hp

I recently purchased a second hand yamaha 4hp 4 stroke second hand. She starts first pull but I notice a very limited amount of water coming from the pisser until the engine was given high revs and then the water was extremely hot. I therefore proceeded to replace the impellor and things still remain the same. I then replaced the thermostat and things still did not change. When the thermostat is taken out I have a continious flow of water through the pisser but when it put back in ,there is only a dribble with no water coming out in a stream until the throttle is opened up, with the water very hot. Is this normal for a small engine and is it safe to run it without the thermostat. Any advice would be appreciated

john are you sure you have the engine deep enough in the barrell . if not the impellor might only be getting water when there is churning in the barrell. if this fails try a set of muffs they might do the trick. make sure cavatation plate is well covered in the barrell.

I have one of these engines. On mine there is a big gush of water at any revs [more than my 80hp main engine] and it stays quite cool. I'd say previous poster could be spot on, the cooling system probably needs more water.

Replace thermostat

Thanks for all the advice. I have replaced the thermostat and it is still the same. If I take out the thermostat I have a perfect stream.