1981 johnson 175 hp overheated!

[wickers]

Hello,

Let me first say that I am just venturing into the world of boating and have no clue what I'm doing!!! LOL I have worked on cars inside and out as a tech for years but this is a first for working on a boat motor.

I recently picked up my first boat; a 1981 skeeter with a 175 hp Johnson. I took it out on the lake after getting it and everything was great, the motor ran perfect. On my second time out I unloaded the boat off the trailer and shortly after leaving the trailer an alarm started going off. So I started toward shore and I noticed the motor power was less than half. Before I could get it docked it started smoking from under the motor cover.

I shut it off and swam the boat back on the trailer. When I got home I called my uncle and he came over and put a set of muffs on the motor and we started it back up. No water was making it out the exhaust or out the pee hole (As cars don't have these, I didn't know to check it at the lake. My fault :facepalm The motor reved up fine but again there wasn't a load on it so I don't know if thats a good sign or not. We didn't let it run very long before shutting it off.

Then yesterday I removed the gearcase so I could get the water pump off and the pump was destroyed. No vanes at all left and there was pieces of the vanes actually melted to the housing. Also there were chuncks everywhere.

I plan on checking compression and if they check ok then replacing the water pump and thermostats. Then hope for the best.

My question to everyone; Is there anything else on these that I should also check/replace?

Also if everything checks ok how can I hook up a water temp and water pressure gauge on each cylinder?

 

[emdsapmgr]

Re: 1981 johnson 175 hp overheated!

You already know the overheat system works. By replacing the impeller and both thermostats, you should have your cooling issues behind you. When you have the thermostat housings apart, make sure the nylon pressure relief valves are not heat-deformed. It's hard to tell much about the engine when idling on the trailer in the back yard. That engine will seem to run just fine on 3 or 4 cyls. It's a different story when you get the boat back in the water-you need all 6 working. When that engine overheats, the pistons swell and can cause the rpm's to decrease. They can even lock up inside the cyls if they get hot enough. For that reason, I'd definitely do a compression check on the engine. Normal compression should be around 95 lbs. When you start the engine back up, you might want to check the cyl head temps with a laser temp gun. (you can rent one locally from an auto parts store.) I'd be looking for 143-145 degrees at idle. Make sure your telltale is working.

 

[wickers]

Re: 1981 johnson 175 hp overheated!

well

 

[wickers]

Re: 1981 johnson 175 hp overheated!

Well just got a few extra minutes and did a compression check. The pressures I got were 100, 85, 100, 100, 105, and 110. So I guess I'm gonna have to pull the head on that side and see why I have one that is 85. Also I pulled both thermostat covers off. The spring and pressure relief valves on both heads were covered in what looked like a white melted plastic? Is the pressure relief valve made of plastic? It was on both sides of the valve and starting to run down into the cylinder head cover.

 

[boobie]

Re: 1981 johnson 175 hp overheated!

You should also be concerned where all the pieces of the water pump vanes went as they could cause an overheat prob later on. Another thing to think about is the condition of the water deflectors in the block under the heads.

 

[emdsapmgr]

Re: 1981 johnson 175 hp overheated!

The pressure relief valves in each thermostat housing are nylon. Do those nylon valves appear to be heat-distorted at all? Once they get heat-distorted, the won't function properly. That can cause cooling problems once the boat gets up on plane. Agree, pull the head on the low compression side for a visual inspection of that low piston/hole.

 

[wickers]

Re: 1981 johnson 175 hp overheated!

You should also be concerned where all the pieces of the water pump vanes went as they could cause an overheat prob later on. Another thing to think about is the condition of the water deflectors in the block under the heads.

Yeah I've decided to pull both heads, exhaust cover, and water passage cover and check it all out. Right now I can shoot water up the tube that connects to the water pump and I get a dribble out the telltale, stream out the exhaust, and nothing makes it to the cylinder head covers.

The pressure relief valves in each thermostat housing are nylon. Do those nylon valves appear to be heat-distorted at all? Once they get heat-distorted, the won't function properly. That can cause cooling problems once the boat gets up on plane. Agree, pull the head on the low compression side for a visual inspection of that low piston/hole.

The valves are nothing more than a washer now with the ends melted off!! When I get home today I'm gonna start teardown. Is there a way to replace the grommet on the top of the water tube without taking the exhaust housing apart. (I really don't want to pull the powerhead off if I don't have to.)

 

[wickers]

Re: 1981 johnson 175 hp overheated!

So I pulled the heads and exhaust cover off and the pistons looked fine and the cylinders still had their crosshatch. The telltale elbow, hose, and nipple were plugged with water pump pieces. The water passage deflectors were in their proper places but I'm gonna replace them anyways. I wasn't able to get the water passage cover off because I didn't have a puller to remove the flywheel off with. I'm gonna get one so I can remove it and see inside the passage.

Now heres the bad part, I found the piece in the picture in the water passage of the cylinder head with the low compression. I have no idea were it came from or even what it is. If anybody knows what it is please let me know.

 

[emdsapmgr]

Re: 1981 johnson 175 hp overheated!

Your mystery part is unusual, with the tapered ends. Any chance it is an internal component of the thermostat?

 

[boobie]

Re: 1981 johnson 175 hp overheated!

It looks more like a roller from a closed bearing.

 

[wickers]

Re: 1981 johnson 175 hp overheated!

Your mystery part is unusual, with the tapered ends. Any chance it is an internal component of the thermostat?

Both thermostats are complete, no missing parts. Plus this was found in the coolant passage that surrounds the cylinders in the block next to the middle deflector. So if I understand how the water flows in this motor it goes around the cylinders before it makes it to the heads or thermostats. So it should be from something in the block or before.

It looks more like a roller from a closed bearing.

Thats what I thought but how could it get into the coolant passage???? There isn't any way for any bearing pieces from the block; i.e. crank; to get into the passages, right or am I wrong? The impeller housing plate didn't look damaged so I don't think it could've come from the gearcase. So I'm at a loss. I'm tempted to tear the entire motor apart from powerhead to gearcase, just cause I'd hate to put it back together just for it to lock up or worse because of this piece not being where its supposed to be.

I just don't know if this is like you said a roller or a locating pin or what it is. I have a pulley puller now, but I'm gonna wait until this weekend before I tear further into this motor, maybe someone will help me figure it out before then.

 

[boobie]

Re: 1981 johnson 175 hp overheated!

This may be off the wall, but could it have been the pin that holds the water pump impeller in place ??

 

[wickers]

Re: 1981 johnson 175 hp overheated!

This may be off the wall, but could it have been the pin that holds the water pump impeller in place ??

No the pin on this one is more of a wedge that holds the impeller in place and it was still in place. But thanks for the help!

 

[boobie]

Re: 1981 johnson 175 hp overheated!

Back in '81 and newer I remember pins for water pumps. As the yrs go buy the w/p kits change. This could have been an old pin from some w/p yrs ago to end up in the cooling system.

 

[wickers]

Re: 1981 johnson 175 hp overheated!

Back in '81 and newer I remember pins for water pumps. As the yrs go buy the w/p kits change. This could have been an old pin from some w/p yrs ago to end up in the cooling system.

Ok boating fans, we have a winner!!! After reading this post I went back through the product catalog of my motor and if I order the pin by itself it is the part in question but if I order a water pump kit it is the updated version with the plastic pin. I guess whoever changed the w/p in the past didn't worry about where it went.
Thank you boobie for your help, this answers alot of questions and helps ease my mind a little about putting the motor back together and trying it out before I do a complete rebuild.

Also to note I will be making sure the water passages are free and clear of any foreign objects before putting it back together. I hope to have it done so I can take it out 1 last time before the weather turns. (Its now Thursday and they're calling for snow on Monday, so I don't know if this will work out.) I would like to know so I can make it a winter project if it needs rebuilt. Fingers are crossed!!!

 

[boobie]

Re: 1981 johnson 175 hp overheated!

Don't forget the water deflectors in the block.

 

[orbanp]

Re: 1981 johnson 175 hp overheated!

So I pulled the heads and exhaust cover off and the pistons looked fine and the cylinders still had their crosshatch.
...

If you have the crosshatching fine, it would be worthwhile to put new rings on the pistons, they are probably not as free as they could be. I am not sure what the compression should be on that engine, but what you have is not the best.
Is your compression tester accurate? Could you measure a "known" good engine?
If nothing else I would free up the rings.

Good luck, Peter