1976 Johnson 35HP cooling issue

[dtrojcak]

I just purchased a 14' flatbottom boat with a 1976 Johnson 35hp outboard on it.
Motor cranks fine and I get a fine spray of warm water out of the exhaust relief holes just like it's supposed to. There is also a couple of holes a few inches above the water line that have a steady stream of warm water coming out.

The problem is once it warms up enough to open the thermostat, the spray out of the relief holes stops.
The other holes continue to have a steady stream of water, but the water is cold now.

From what I've researched so far, the small spray of water out of the relief holes is supposed to increase once the thermostat opens.

Any suggestions on what I need to check/replace?

 

[F_R]

Re: 1976 Johnson 35HP cooling issue

The question from here has to be is it overheating or are you just worrying about the water spray? And just which lower holes are you talking about, the two near the lower mount? Those two hole are drainage of water that has escaped the water pump through the drive shaft hole, absolutely normal. They have nothing to do with cooling, just getting rid of water that otherwise would cause severe damage.

I hate to tell you this, but the 1976 35hp was a poorly designed dud from day one. Overheating was way too common, even on brand new motors. The reason was poorly designed water intake to the pump. It takes virtually nothing to block the flow. I'm saying that prior overheating may have burned/destroyed some gaskets or seals, such as the water tube grommets.

 

[dtrojcak]

Re: 1976 Johnson 35HP cooling issue

The question from here has to be is it overheating or are you just worrying about the water spray? And just which lower holes are you talking about, the two near the lower mount? Those two hole are drainage of water that has escaped the water pump through the drive shaft hole, absolutely normal. They have nothing to do with cooling, just getting rid of water that otherwise would cause severe damage.

I hate to tell you this, but the 1976 35hp was a poorly designed dud from day one. Overheating was way too common, even on brand new motors. The reason was poorly designed water intake to the pump. It takes virtually nothing to block the flow. I'm saying that prior overheating may have burned/destroyed some gaskets or seals, such as the water tube grommets.

Yes it is over heating and yes I'm worried about the spray. The spray stops after the motor warms up.
Yes the holes near the lower mount. They always have water coming out of them. I know that is normal. However when the spray stops, the water coming out of the lower holes changes from warm to cold water.

It may be a "poorly designed dud", but this one has been running for almost 40 years.
This one has set up for about a year before I bought it.
The "poorly designed" intake is not blocked as it works fine when the motor is cold. The problem happens once the motor warms up, which probably means it happens when the thermostat opens.
My guess is once the thermostat opens, the water pump is not strong enough to pump water into the now open cavities.
I just wanted a second opinion before I tear into it to replace the pump.

 

[racerone]

Re: 1976 Johnson 35HP cooling issue

You should always install a new impeller when you buy a used motor !

 

[dtrojcak]

Re: 1976 Johnson 35HP cooling issue

You should always install a new impeller when you buy a used motor !

I've been doing some more "google research" this morning along with a few phone calls from friends who own boats.
Your advice is the same as what I've been finding.

Basically, the conclusion has been, if you don't know how old the impeller is, replace it.

Next question, is this easy enough for a first time boat owner to tackle?
I'm not scared of mechanical work. I work on my diesel truck, tractors, lawn mowers, trailers, etc.
I just don't want to get into something too big.
From what I've read so far, it doesn't sound too difficult, just time consuming.

 

[racerone]

Re: 1976 Johnson 35HP cooling issue

Simple tools and nothing to it at all.------I believe you disconnect the shift rod after taking off the oval plate on the exhaust housing.----One bolt must be REMOVED to disconnect the shift.----Look on -----shop.evinrude.com-----------for the parts blow-up.

 

[F_R]

Re: 1976 Johnson 35HP cooling issue

The water from the holes near the mount normally is cold because it has not passed through the cooling system. It is coming directly from the pump housing.

Sorry if I offended you, but you obviously don't live in Florida. Those motors won't run in our fresh water lakes and rivers because the water weeds block the intake holes in nothing flat. It wasn't a matter of 40 years, it sometimes was more like 40 minutes. I know, because I'm the guy that had to fix them under warranty.....then tell the guy it won't go where he wants to go.

 

[dtrojcak]

Re: 1976 Johnson 35HP cooling issue

Simple tools and nothing to it at all.------I believe you disconnect the shift rod after taking off the oval plate on the exhaust housing.----One bolt must be REMOVED to disconnect the shift.----Look on -----shop.evinrude.com-----------for the parts blow-up.

Thanks for the info.

The water from the holes near the mount normally is cold because it has not passed through the cooling system. It is coming directly from the pump housing.

Sorry if I offended you, but you obviously don't live in Florida. Those motors won't run in our fresh water lakes and rivers because the water weeds block the intake holes in nothing flat. It wasn't a matter of 40 years, it sometimes was more like 40 minutes. I know, because I'm the guy that had to fix them under warranty.....then tell the guy it won't go where he wants to go.

No you didn't offend me.
I realize a blocked/clogged intake would cause problems.
I haven't put the boat in the water yet, only testing at the house using muff and then a trashcan filled with water, so nothing but clean water.
Everything would work correctly until the engine warmed up.
From what I've learned, the impeller is weak. When the thermostat opens, the pump is too weak to pump water through the now open passages.

 

[F_R]

Re: 1976 Johnson 35HP cooling issue

Well of course, that is the first thing to check before looking for something more complicated. First things first, as they say.

 

[dtrojcak]

Re: 1976 Johnson 35HP cooling issue

Simple tools and nothing to it at all.------I believe you disconnect the shift rod after taking off the oval plate on the exhaust housing.----One bolt must be REMOVED to disconnect the shift.----Look on -----shop.evinrude.com-----------for the parts blow-up.

Are there any other seals or gaskets that should be replaced once this is opened up?