1989 Evinrude 25HP Outboard - Overheating and Water Flow Problems

[Viking59]

Motor starts and runs great. Initially water flows okay while the motor runs at slightly higher RPM's at startup. Once the idle settles, the water flow starts to cough and the stream is no longer steady. The water that makes it out starts to get hot, as does the rest of the motor. Eventually the stream will completely stop.
This motor has seen a lot of salt water use but many parts have been replaced...
New impeller has been installed and then double checked when water flow problems persisted. The line for the pump to the head is clear. Brand new thermostat installed. Exhaust housing was opened up and inspected. Pee tube is clear.

Any thoughts? I feel like I've replaced everything that could cause issues with the water flow. Is this motor nuked??

Thanks

 

[racerone]

Remove cylinder head if bolts will come out.----There are 3 " water deflectors " that guide cooling water around the block.----They may be in bad shape and blockage may exist.

 

[gonefishin485]

you might also want to try and remove your thermostat and see if that makes a difference before you pull the head off. if you live in a warmer climate like i do here in south louisiana, youll never miss the thermostat, but if you live and boat in a cooler climate your going to want that thermostat in there.

 

[jrs_diesel]

The thermostat is there not only to regulate engine temperature, but also water flow in the engine block. Running without the thermostat generally allows the motor to run colder than normal, leading to more deposits, build up and stuck pistion rings. Worst case the water doesn't fill the block completely and you end up with hot spots, uneven and unregulated cooling. Can you run without it, yes. Is it good for the engine in the long run, nope.


My 9.9 had cooling issues similar to yours. Mine was also a salt water engine. Turned out the upper water tube grommet had swelled and almost completely closed off the water supply to the block. I had to separate the powerhead from the midsection to get to it. Since I had to go that far into the engine I also popped the exhaust plate, cylinder head, and thermostat housing off and cleaned all of the water passages out with my Dremel. Put new gaskets on too. I have had zero cooling problems since.

 

[Viking59]

Thanks everyone! Sounds like I have my work cut out for me....