1981 johnson 115 hp overheating

[bojango541]

Hello,

I have a 1981 115 hp 4 clyinder johnson on my bass boat. It has been over heating. We took the lower unit off and checked the impeller/water pump, and it looked brand new. We then took it out again and by pulling the heat sensor wires were able to narrow it down to what side of the motor/2 cyinders were overheating. Tried blowing through the tube where water circulates through the block and was able to do so without and issues, so i dont think thats clogged. Anybody know what the issue could be? Thanks Nick

 

[bojango541]

Re: 1981 johnson 115 hp overheating

Also, we used a heat gun, one side of engine was about 172 degrees and the other side setting off the overheating siren was 184

 

[iwombat]

Re: 1981 johnson 115 hp overheating

Time to replace the thermostats. Also, how did you determine your impeller "looked good". You should replace it every couple of years or so.

 

[tashasdaddy]

Re: 1981 johnson 115 hp overheating

you have 2 thermostats, one for each head. they are extremely hard to get to. they are on the top of the exhaust housing, below the bubble back. diagrams here, look at exhaust housing item # 78.

 

[bojango541]

Re: 1981 johnson 115 hp overheating

I just bought the boat last year and the guy said he just put a new one in, ive seen a bad waterpump, and i could just tell this was good. Should the overheating siren not be going off at that temp? the side that was going off was definately hotter than the other side.

 

[bojango541]

Re: 1981 johnson 115 hp overheating

you have 2 thermostats, one for each head. they are extremely hard to get to. they are on the top of the exhaust housing, below the bubble back. diagrams here, look at exhaust housing item # 78.

Where is the diagram?

 

[iwombat]

Re: 1981 johnson 115 hp overheating

184 is certainly not enough to trigger the overheat alarm, but it is still too hot for comfort. The t-stats should be kicking in at 160 (if memory serves).

 

[Sodaguy2]

Re: 1981 johnson 115 hp overheating

Hey,
I am working with Bojangle on that boat, any one have a link to the parts diagram for the themorstat, also my thermo gun only reads the externo temp, but did help me figure witch side to start with, my original plan was to pull the head on that side to check for blockage, (wonder son had it beach it muck for a while after I got his other new toy running), but I think I will go with the theorstat first. Thanks

 

[emdsapmgr]

Re: 1981 johnson 115 hp overheating

Each thermostat will open at 143 degrees, so the engine should idle at 143-155. It will sound an overheat horn at 212 and shut off when it gets back down to 175. I agree with Wombat that it is running too warm. You need to pull the thermostat housing apart and check (probably replace) both stats. Also, check the pressure relief valves, as these nylon parts can deform due to heat and cause flow restrictions. Finally, the thermostat valve body has either one or two pinholes in it-depending on year. This hole(s) need(s) to be open to keep from overheating.

 

[iwombat]

Re: 1981 johnson 115 hp overheating

Thanks for the 143 correction.