overheated johnson 40

[bigd559]

I own a 40 hp Johnson 1973.<br />When I was winterizing it this fall, I did not have enough water in the garbage pail I was using and it was not getting enough water and so it overheated. I was spraying Johnson tune-up cleaner into the carburetor for 10 minutes at high idle at the time. The engine did get hot but did not scorch the paint. <br />I filled the garbage can with enough water and it runs cool now but seems to smoke a lot. What should I do to test the extent of any possible damage? <br />Should I replace the head gasket and water pump impellor. What else should I replace or inspect for damage. I also am going to rebuild the carburetor because it was smoking a little from before.<br />Thanks for any help,<br />derek

 

[R.Johnson]

Re: overheated johnson 40

That is hard to answer, how hot? how long? Do a compression test,and take a look at the water pump housing, and impellor.

 

[bigd559]

Re: overheated johnson 40

very hot, 10 minutes. What is acceptable compression for a 40 hp? Water pump is working fine. But I suspect it has not been replaced for a while. I just bought the boat and motor last summer and so I don't know how it was maintained.<br />thanks for your reply,<br />derek

 

[Paul Moir]

Re: overheated johnson 40

Welcome to Iboats, BigD559!<br /><br />If you're unsure of the age of the impeller, it's time to replace it. They need to be replaced every couple years at least anyway. Pump kits are around $15 (if the housing is good) and are pretty easy to replace on your engine.<br /><br />The speced compression for your engine is no more than 10% variation between cylinders. There's no acceptable PSI value given, but (very) generally speaking 90psi or better is good. Tell us what you measure.<br /><br />Also, have a look at the sparkplugs. If they're not new and one is super-clean at the firing end, it's a good sign of water-intrusion into the cylinder. Note any differences between the top and bottom anyway.<br /><br />Tell us what you find!<br /><br />(PS - did the engine bog at all when it got hot?)

 

[bigd559]

Re: overheated johnson 40

No it did not bog after it got hot. Do I have to change the oil in the lower unit again after testing it? It is stored outside in Indianapolis.<br /><br />I will replace impeller with kit. Last time I did a compression test it was about 110 lbs on each cylinder. I will do it again. Must it be done with the engine warm?<br /><br />Thanks so much for the help!