I have twin yamaha 4 stroke f250's on my boat. This year the overheat alarm came on at idle. I just had the motors service 12 months earlier with new impellers. I had another impeller installed by my tech in barnegate Nj and the boat continued to over heat only at low rpm's. I then replace the two theromstats. The boat still overheated at low rpm's. I let the boat alarm come on at the dock. I hooked the hose attachment to the motors while they were in the water. The boat cooled down and ran normal. I then shut off the hose and hooked the washdown attachment back and the boat ran normal tempeture .My tech pulled the lower unit and confirmed that nothing is clogging system. Does anyone know what this problem could be before I pay to replace every part on my cooling system? I would be greatful for any advice.
