1984 Johnson 35 overheating questions

crmaverick · Sep 30, 2011

I had the boat running fine, newer water pump that pumped a strong stream of water. Had it running on the lake for about a half hour then shut it offfor about 15 minutes, then started it up an ran it for about 2 minutes half throttle and i heard a hissing noise and saw steam coming out the exhaust. The motor was really hot, let it cool down for 15 and started it up briefly and saw steam coming out of the pee hole where water should be, then shut it off right away and got towed back in.

Here are my questions:

Do you guys think its a thermostat and where is it located on the motor?
Could a good water pump fail all of sudden?
Where can I buy these replacements parts?
And do you think I damaged the motor? It started back up fine again after. (and it didn't get hot enough to the point where it shut itself off, I turned it off)

Thanks everyone

nwcove · Sep 30, 2011

Re: 1984 Johnson 35 overheating questions

id look at the tstat, but it sounds like the classic symptoms of a blown head gasket. very good chance the motor is fine. a compression test would verify a bad headgasket.

crmaverick · Sep 30, 2011

Re: 1984 Johnson 35 overheating questions

So looks like the head is coming off either way, is there a torque sequence/amount I need to follow when putting the head back on?

Are there any write ups on removing the head and t-stat replacement?

thanks

nwcove · Sep 30, 2011

Re: 1984 Johnson 35 overheating questions

cant speak on torque numbers, but if you search the forum, there are good pics of sequence, and probably threads on the tstat.

todd ashley peters · Sep 30, 2011

Re: 1984 Johnson 35 overheating questions

hi there, the thermo is under a triangular plate towards the back of the motor. three screws hold it in place. sounds like it might be the prob. any outboard that deals with johnsons will have the parts. get a gasket too. how old is the water pump impeller and how old is the pump housing.the impeller can go in one trip if a piece of something gets up in there. could have picked up something then blew it out too. it happens. an impeller can seem to work fine at low speed and not well at high speed. if you have not changed it this year or cant remember when, change it. you probibly didnt hurt the motor too bad.

F_R · Sep 30, 2011

Re: 1984 Johnson 35 overheating questions

I don't believe it is a bad thermostat. The pee hole is ahead of the thermostat, so water gets to that first. Even if the 'stat were completely shut/plugged, or whatever, there would be water coming out the pee hole.

You need to go back into that water pump as a first step.

As for your question asking did you hurt the motor----possibly. Did it get hot enough to discolor the paint? If so, there is a good chance of scored pistons and/or burnt gaskets. Not only that, that motor has a plastic pressure relief valve that bypasses the stat. Could have melted the plastic.

Your other question---any Evinrude dealer has or can get the parts you need.

crmaverick · Sep 30, 2011

Re: 1984 Johnson 35 overheating questions

It didn't discolor the paint, so it should be good? Compression still feels as strong as ever. I shut the engine off right away when it started to steam out the exaust.

What is the possibility that the water tube that connects to the lower unit coming off?

I can hear a hissing sound when I crank the motor by hand at the flywheel. This hissing seems to be coming from the middle/lower unit. Anyone know if thats normal?

Either way, I have ordered a thermostat, head gasket and water pump repair kit.

Thanks guys

crmaverick · Oct 1, 2011

Re: 1984 Johnson 35 overheating questions

How do you know if there is any blockage in the cooling system and is there a way to flush it out?

I plan on replacing everything- impeller, gasket + thermostat to cover it all. Anything else I should check for (such as the coolant tube falling off)?

Should I hook it up to the muffs and see if the impeller is still working? (it was showing a strong stream last weekend)

Thanks

Haffiman · Oct 1, 2011

Re: 1984 Johnson 35 overheating questions

Never use muffs to test water pump function, use a barrel. Water level min 5-10" above the split between gear case and leg. (pump under water).
When you have the leg down hook up a hose on the water tube and flush! Start with low pressure, water should only get out through the pee hole. At about 20PSI, the water should start flowing through the pressure valve.

crmaverick · Oct 1, 2011

Re: 1984 Johnson 35 overheating questions

Haffiman said:
Never use muffs to test water pump function, use a barrel. Water level min 5-10" above the split between gear case and leg. (pump under water).
When you have the leg down hook up a hose on the water tube and flush! Start with low pressure, water should only get out through the pee hole. At about 20PSI, the water should start flowing through the pressure valve.

When you say have the leg down, do you mean the lower unit separated from the middle unit? And to hook a hose up directly to the water tube? Where is the pressure relief valve water exit?

Thanks

Haffiman · Oct 1, 2011

Re: 1984 Johnson 35 overheating questions

Yes, lower unit off. The thermostat is spring loaded and at higher rpm's (higher pump pressure) the thermostat gets by-passed. If water start coming down inside the leg as soon as it appears in the pee-hose, the thermostat is 'leaking'. Normally the original OMC thermostats failed in open position, but Yamaha and a lot of the after marked ones fails in closed. To be safe, remove/change and test in hot water, Should open around 145F.

crmaverick · Oct 3, 2011

Re: 1984 Johnson 35 overheating questions

Haffiman said:
Never use muffs to test water pump function, use a barrel. Water level min 5-10" above the split between gear case and leg. (pump under water).
When you have the leg down hook up a hose on the water tube and flush! Start with low pressure, water should only get out through the pee hole. At about 20PSI, the water should start flowing through the pressure valve.

Where is the pressure valve that I should be looking for water? I hooked up a hose today to the copper tube, I had water coming down inside the leg (middle unit). I looked up in there and could see it was from a weap hole.

Is that normal?

Haffiman · Oct 3, 2011

Re: 1984 Johnson 35 overheating questions

Pull out the thermostat and re-test.
Did water come out the pee-hose? (control hose attached to exhaust cover port side)

crmaverick · Oct 4, 2011

Re: 1984 Johnson 35 overheating questions

Yeah water came out the pee-hose (hose that the water normally comes out of when engine is running)

crmaverick · Oct 4, 2011

Re: 1984 Johnson 35 overheating questions

I took apart the water pump. I found that the impeller and housing had failed. Was a newer pump so I guess sand or something got sucked in. Kind of scary, how do I prevent this from happening in the future? Can putting it in reverse cause sand to blown back and sucked into the pump?

F_R · Oct 4, 2011

Re: 1984 Johnson 35 overheating questions

I sort of doubt it was due to sand. By pump housing "failed" do you mean melted?

crmaverick · Oct 4, 2011

Re: 1984 Johnson 35 overheating questions

Yeah I could melted plastic in there and skid marks from the impeller

F_R · Oct 4, 2011

Re: 1984 Johnson 35 overheating questions

My educated guess is the impeller failed first. That meant no water to the powerhead, which meant no water out of the powerhead, which meant no discharged water out the exhaust----which meant the hot exhaust blew onto the water pump housing which is normally cooled by the discharged water coming down from the powerhead. In other words, the melted housing was a RESULT of overheating, not the CAUSE of the overheating.

Exactly what did the failed impeller look like? Did the metal hub come loose from the rubber, or did it shed it's blades, or what? Personally, I'd get a whole new complete water pump kit from an Evinrude dealer.

crmaverick · Oct 4, 2011

Re: 1984 Johnson 35 overheating questions

Impeller looked kind of chewed up, but all there. I ordered a complete kit here on iboats.

Lucky that I caught the overheat right when it started to steam/hiss and I shut it right off. Found out my overheat horn isn't hooked up.

Anyone know where I can get an overheat horn for an 84 Johnson 35 console?

Thanks

Haffiman · Oct 4, 2011

Re: 1984 Johnson 35 overheating questions

If using an original OMC control, it should already be inside the unit.

1984 Johnson 35 overheating questions

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