9.9 engine shutdown

[tlmpontoon]

Johnson 9.9 4 stroke model JIOTEL4SN - Starts and runs @ full power for 15 - 20 minutes then shuts off completely will not restart until motor cools down, tank value open, bulb hard, rebuilt water pump with new impeller and good water flow (happened several times last season before rebuilt), tune up with total change of all fluids, first time out this year and same result tired of getting pulled in.

 

[MegalopsAtlanticus]

Is there a new thermostat in there?

I've had my thermostat rusted shut (or plugged with shells, etc) and while the telltale is still peeing like a champ, no water was cooling the head.

It behaved just like you are describing. Until the head gasket finally blew apart, haha.

But where I live, the water temps never get below 70 degrees. So I've pulled the thermostat entirely and replaced it with a small stainless washer to provide some back pressure. While I know that is not standard procedure (nor recommended) down here in the super-shallow Everglades I'd rather have the engine running too cool than to continually have the thermostat plug up with debris every week.

 

[scout-j-m]

I've had a powerpack fail due to heat before. Motor would run great for about 10 minutes but it would sporadically drop a cylinder after that. Was a pain in the butt to diagnose since it was a 3 cylinder and even then only happened at high speeds. Since you are getting a total shutdown, you could run some electrical checks on the water immediately after shutdown to diagnose. start with spark at the plugs and work your way back up the ignition system. I can't help on specific readings though.

If you want to check for overheating, do a hand check after shutdown and if you can leave your hand on the block for a few seconds without much discomfort you know you are good. If it seems really hot get a $20 infrared temp gun and check the block temps while it is running well and then after it shuts down. Those temp guns are super handy around the house so even though they are cheap the cost is easily justifiable.

Also, even though fuel delivery doesnt appear to be the problem, to monitor fuel delivery I like to put a clear in-line fuel filter on the line between the fuel pump and carb. With the hood off it is easy tell if the fuel pump is doing its job.