Starboard cylinders overheating, but no thermostat installed

[Sobbleson]

I have a 1978 Johnson 85 hp. Boat sat for about 5 months but the motor was really struggling to run the last time I was out. Turns out I had a misfire (probably from when I got the boat 1 year ago). I replaced all 4 coils, took the boat out a few days ago and she ran better than ever! After a little over 5 minutes of sustained WOT, we noticed the motor was smoking bad! I’m not sure, but I think it also sounded like it was hissing. The tell tale was a steady cool stream. We shut off the motor, drifted for a bit, then turned it back on and hobbled back at low idle/forward until we reached the dock. Starboard cylinders were too hot to touch, port were hot but bearable to touch.

That night I removed the water hoses from the thermostat cover to the cylinders and starboard side was bone dry and had buildup of granular stuff (not enough to block flow and would probably be muddy if it had been wet). Port hose was wet and not as bad buildup.

Last night I removed the thermostat cover and there were no thermostats! Previous owner must have removed them. The port side relief valve and spring came free and weren’t stuck. The starboard side relief valve was stuck to the grommet, but it pulled right off with little effort.

So my question: can the “stuck” starboard relief valve be keeping water from making it to the starboard cylinders? Water should be making it to the starboard cylinders since there was no thermostat, even if the relief valve was stuck right? What is causing the water not to reach the starboard cylinders?

Note: I changed the impeller with a kit last year. So I’m not sure it’s the impeller since the tell tale is also functioning. I haven’t pulled off the lower unit since last year. I’ll look at the impeller if everyone thinks that’s the issue.

 

[saltchuckmatt]

Pop off opens at high speed so yes that could be it otherwise clogged water passages on the starboard side.

Sound like the past owner knew there was something wrong and Mikey moused it.

 

[Sobbleson]

Pop off opens at high speed so yes that could be it otherwise clogged water passages on the starboard side.

Sound like the past owner knew there was something wrong and Mikey moused it.

after more research, I agree that there’s some blockage on the starboard side. Do you know if the water comes from the starboard cylinder, through the water hose, and then to the thermostat? I assumed it had to pass the thermostat first, then go through the water hose, then to the starboard side.

 

[racerone]

Water from the tell tale does not go through the block.---So it is always cool.----Water goes through the thermostats last.----There are 4 ( 2 per side ) water diverters in the water jackets.---Perhaps these are out of place and blocking water flow.-----Water does NOT go through these diverters.----They merely guide water through the water jackets.----Have you tested the over heat horn ?----Do a compression test. for future reference.---Post the numbers here.

 

[Sobbleson]

Water from the tell tale does not go through the block.---So it is always cool.----Water goes through the thermostats last.----There are 4 ( 2 per side ) water diverters in the water jackets.---Perhaps these are out of place and blocking water flow.-----Water does NOT go through these diverters.----They merely guide water through the water jackets.----Have you tested the over heat horn ?----Do a compression test. for future reference.---Post the numbers here.

Thanks for the info! I found some clipped wires in the control that was going to a speaker (I think) - is this the overheat horn? If not, then I have no idea where it is and I’ve never heard a horn go off while operating the boat.

I’ll do a compression check tomorrow if I can get a tester. After that I think I’ll try pushing water through and if I can’t get it through the starboard side then I’ll take off the head cover and look for blockages. I ordered a gasket kit, so I’ll replace those while I’m at it all.

 

[racerone]

So it sounds like the previous owner had issues.----Then put that horn in the control box out of service.-----Do the compression test before spending any more beer tokens on the motor.-----The cylinder head needs to come off to replace the diverters..---Just 10 bolts using a 1/2" socket I think.

 

[Sobbleson]

Compression was 90 on each cylinder.

I then took off the head cover and think I found the problem… haha

Hopefully it cleans up easy. I have gaskets coming at the end of the week.

 

[racerone]

Test compression with another gauge.----At 90 PSI they appear to be low.

 

[tphoyt]

Agreed on checking with another gauge to confirm these numbers. Do you plan on pulling the heads to check the diverters. I’m sure you will find even more crud there as well.
Best

 

[Sobbleson]

Removed the starboard (problem side) head and there were no blockages, diverters were in place, and all looked pretty good. The chamber walls still have the cross hatching and I can’t see or feel any scrapes/damage.




I just finished removing the port side head and cover. There was a tiny bit of buildup in the cover, but sooo much better than the starboard one.

 

[racerone]

replace the diverters.

 

[Sobbleson]

@racerone - I ordered new diverters.

I’m worried there’s another blockage somewhere since the head was basically clean on both sides (looks like the bigger water jackets allow more water to flow than in the head cover) and just the head cover was blocked up. I’m going to take off the outer exhaust cover that’s between the cylinders (see attachment) and check for blockages there.

Would there be any other places a blockage could be that causes the starboard side to have less water? I plan on checking the impeller soon too.

 

[racerone]

Outboard motors need a new impeller if you do not know how old it is.----And a new one about every 5 years or so.

 

[Faztbullet]

Crosshatching means nothing as they are microscopic. The cylinder has wear as the dark spot around exhaust port..this is from piston side thrust.

 

[Sobbleson]

Outboard motors need a new impeller if you do not know how old it is.----And a new one about every 5 years or so.

I changed the impeller last year (around a year exactly). I'll look at it any ways.
Would the lower amount of water coming out of the starboard side be because I wasn't under load (tested on muffs) and there was water leaking from the muffs plus the starboard head is a little higher than the port side?

 

[Sobbleson]

Crosshatching means nothing as they are microscopic. The cylinder has wear as the dark spot around exhaust port..this is from piston side thrust.

Is it enough wear from metal friction that is causing more heat on the motor?

 

[Sobbleson]

I removed the exhaust cover and there were no blockages. Any other spot you all can think of besides the impeller that might be blocked?

 

[Sobbleson]

I cleaned both heads, head covers, and the exhaust cover. I replaced the gaskets with new ones, swapped out the water pump, and installed the new thermostats. Took the boat out today and it worked flawlessly! Looks like cleaning out the blockages and a new water pump (even though the last one wasn’t in bad shape) did the trick - no more overheating. I will check compression again soon and torque the screws down again according to the manual. Also need to flush it with some salt away or vinegar.

Thanks for all the advice!