1989 175 Johnson. It runs fine until temp warms up to the point where the thermostats are supposed to open. Then, the temp rises rapidly, and the overheat horn sounds.<br /><br />I've removed the old thermostats (they were clogged with sand and grit) and replaced them with new, clean thermostats. But, this was no help. I was advised that the engine is probably "sand impacted." I then removed the thermostats and ran the engine at idle in a tank. I hoped this would flush any sand out of the powerhead circulation orifices. (I was advised not to exceed idle RPM with the thermostats removed. Since the engine overheat warning functions okay, is this restriction really necessary in this case?)<br /><br />When I replaced the thermostats, launched the boat, and ran the engine at higher power settings, it overheated again.<br /><br />If the engine is actually sand impacted, is there something other than plain water that I can use to try to clean out the passages? A mixture of water and laundry detergent? Water and 409? Or, am I stuck with disassembling the power head and cleaning out the passages manually? Any suggestions will be greatly appreciated.
