1999 Johnson 115 Running Hotter on Starboard Side

[Captain Jeff]

1999 Johnson 115 (60 Degree V4). I was running it in the driveway and noticed the starboard cylinder head and thermostat housing was hotter than the port side. I checked with a non-contact infrared thermometer and found the port side was running around 105-108 F and the starboard was running between 130-143 F (too hot to touch for long). The lower cylinders on each bank ran cooler than the upper. This is after running 5-10 minutes between 900-1,500 RPM on earmuffs.

There is a very strong telltale stream. I replaced the thermostats two years ago. The boat has been used 95% in freshwater. I just replaced the complete waterpump with an OEM pump kit but I don't think that has anything to do with it. This doesn't seem normal, please let me know your thoughts. Thanks!

 

[boobie]

Swap the thermostats once from side to side and see what happens.

 

[oldboat1]

And figure out how to test in a tank or in the lake, as you can't tell much about pump operation running on muffs. Water level has to be at least three or four inches above the water pump. Run it at idle -- likely to be somewhere around 750 rpm with back pressure.

 

[Captain Jeff]

Thanks guys, I appreciate it. Does anyone know what the operating temperature is supposed to be on this engine?

 

[oldboat1]

Depends a little on lake temp, but look for 120-140F, give or take. 160F is too hot

 

[Captain Jeff]

No Title

Well guys, I swapped the thermostats, springs, and caps and the port side was running at 159 F while the starboard was in the 130's F. Obviously something must be up with that thermostat. I am going to try swapping in one of my old ones that I saved. I also noticed the inner lip/cup area of that thermostat cover is slightly melted. It looks like the thermostat is actually hitting the melted part as you can see an indentation in the melted part. Please see pic and let me know what you think. FYI this was still on earmuffs not the lake.

 

[Captain Jeff]

So I excercised the little metal plunger/flap on the "bad" thermostat with a pocket knife blade. I noticed it has a slight rattle now when you shake it. I ran the boat again and now both thermostat housings are running in the mid 140's F. I am thinking it was just a stuck thermostat and the opposite bank was over cooling because this one didn't open and most cooling water got diverted to the other side. I also grounded both tan temp sensor leads and got the Hot warning on the dash so hopefully the actual senders work. At least I know the alarm works. Any thoughts?

 

[boobie]

Good job......