1967 Nautique running hot!

We determined that the lake pump was on upside down by placing a clear hose between the lake pump and the thermostat housing and filled it with water. When you crank the engine the water should be pushed up towards the thermostat housing....if it is sucked down towards the lake pump then the pump is on upside down.

Other things to consider.

Remove the pick up hose from the bottom of the lake pump and ensure that it is not clogged by flushing it with a garden hose....water should exit through the pick up screen on the bottom of the boat.

Remove the lake pump and check your rubber impeller...one of the primary caused of over heating is a lake pump impeller that has broken down, became stiff and old. These impellers are typically only good for a couple of seasons and it is recommended that they be changed annualy. You should inspect the impeller for missing fins, cracking, hardening. If the impeller has broken down look for pieces of the rubber impeller in the line between the lake pump and the thermostat or where ever the line from the lake pump goes to...if you find impeller here look for it in the thermostat area and other lines too.

If your impeller seems to be ok then I would try changing the thermostat....perhaps it has stopped working and is not opening or closing as it should.

If all else fails look for kinked water lines, or water lines with holes in them. If the line is obstructed water will not make it to the engine, and if the lake pump is sucking air due to a hole in a hose or due to a loose clamp it will not prime and circulate water.

If your boat was hot enough to crack an exhaust manifold I would recommend that after you get it running cool that you change the oil after the first few trips to the lake...there is a good chance that you could have cracked the engine block else where and you will find evidence of water in you oil.

I would also recommend that you change the trans. fluid after all is fixed...hot oil causes the friction material on the cluch plates to break down and the heat will also cause the trans fluid to loose some of its lubrication ability....


Good luck

79 Mustang.