1976 Johnson 6 Horse Cooling System Conundrum

[Phree Refill]

Just recently aquired this 6 horse Johnson Seahorse and it runs like a top but the cooling system is ?clogged? somewhere. When you first fire the engine up water will flow through the cooling system and out the blow hole, but after about 15-20 seconds when the engine starts to get warm water stops flowing out the blow hole. The guy I bought it off of runs an outboard repair shop and he already replaced the water pump and thermostat in it and it still has the same problem. He did not tear the engine apart any further because whoever brought him the engine decided they didn't want it anymore. So this repairman sold it to me for what he had in it in parts and labor.

This motor is in excellent shape it just needs this cooling issue fixed. I've read on many different posts on this forum about other people who have taken the same course of action (replace water pump and thermostat) and still can't get the water to flow properly. I've seen several get pointed to a rubber seal at the top of the watertube that goes bad and expands over time and clogs the water flow. Should inspecting the aforementioned seal be my next mode of attack or should I try some other remedies first?

 

[tashasdaddy]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

if i am correct, 76 6hp did noy have a tale tell, water droplets or mist came out he exhaust relief ports on the back of the leg. i would remove tstat and lower unit, connect water hose to the water tube on motor an flush. then flush the block.

 

[Phree Refill]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

if i am correct, 76 6hp did noy have a tale tell, water droplets or mist came out he exhaust relief ports on the back of the leg.

You are correct. It does not have a tale tell but rather a big central blow hole type feature. Forgive my newbie ignorance

If after I flush the water tube and block and I still have water flow issues, what would you suggest my next action be?

 

[Phree Refill]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

Well I tore the engine apart last night to check the cooling system. No clogs in the water tube from the water pump up the shaft to the powerhead. Took the thermostat out and put it in a pot on the stove and it starts opening up at 145 degrees. Hooked one of those garden hand sprayers (you know the kind you pump the handle to create pressure inside the canister) up to the water intake bore on the bottom of the powerhead and gave the sprayer a few pumps and water flowed just fine through the powerhead all the way to the thermostat housing. I did notice a small hole just under the intake bore on the bottom of the powerhead that water was coming out of. I assumed it was some kind of water pressure releif bore in case too much water was drawn up to the engine. The hole was only about the size of the point on a ball point pen.

After I knew I had water flowing fine to the thermostat, I hooked the hand sprayer up to the out-port of the thermostat housing and gave it a few more pumps and it sprayed water all the way through the powerhead and out the exit port on the bottom of the powerhead. It never built up pressure anywhere and it would only take a few pumps of the sprayer to get water flowing though. I even tried pumping the sprayer really fast to get the water pressure up to really blast out of the powerhead but the pasage was so open I couldn't ever get enough pressure built up. So I'm convinced there is no blockages anywhere in the cooling system.

So that brings me to my next question. If the cooling system seems to be just fine, what else could be causing the engine to overheat? And also, being no blockages in the cooling system, I'm really boggled as to why once the engine gets warm, water stops flowing out the "blow hole" on the back of the shaft. Could it all go back to the water pump thats in this thing? It is my understanding that some of these engines have 2 or 3 different pumps you can put in them. The impellar is brand new but the water pump hasn't been replaced. Could upgrading to a more efficient water pump possibly solve my problem?

 

[crxess]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

Incorrect / impeller
missing /damaged impeller key - slipping
Impeller housing / plate / seals worn out - damaged.
Water Intake restricted / blocked

Sounds like water circulation is weak. T-stat opens, relieving pressure and water trail disappears.

 

[Phree Refill]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

I will prolly go ahead and look into upgrading to an entirely new water pump. Just a quick thought though, while it is apparent something in the cooling system doesn't seem to be functioning up to par, could there be something pertaining to the engine that is aiding to the overheating issue? Like its running to lean and the engine is heating more than it should or perhaps the spark plugs in it are too hot for the engine?

 

[crxess]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

Work out one issue at a time.
Poor / no water flow will overheat motor and can cause lean burn symptoms.
Once you get good circulation it may show other issues or things might go back to normal.

 

[jay_merrill]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

As far as I know, there are only two water pump variations for this motor. One has a metallic housing and an impeller that is about 2.5 - 3 inches in diameter. The other has a black plastic housing and an impeller that is much smaller. This unit also has a metal cup, into which the impeller fits. Either one should work just fine.

The rubber seal at the top of the water tube is a grommet which is identical to the one located at the other end of the tube, in the top of the water pump housing. They do sometimes cause problems, in that they can roll inward, as the tube is inserted into them. When this happens, the tube doesn't penetrate into the grommet completely and the pressure against the rubber can close it. Unless your water tube was replaced recently, I wouldn't think that this would be your problem. I also don't think you would have good water flow initially and then not have it, if this were the problem.

While I can't think of any reason why a t-stat opening should cause cessation of water flow, if you think that is the case, I would remove it to test the theory. If you then fail to get water flow initially, we'll have to scratch our heads a bit to figure out what could be happening. If not, I guess we'll still be scratching our heads, but will consider other issues.

 

[jay_merrill]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

I think I may have firgured your problem out. I've reviewed an OMC service manual for a 1974 Johson 6hp motor and looked at a parts motor that I have that is a little older than yours, but should be set up the same way.

When the thermostat is closed in your motor, water flows primarily to a bypass circuit in the cooling system. While there is a small bleed valve (its actually an orifice) that allows a small amount of water to flow through the entire system, most of the water bypasses and comes out the water outlet in the midsection. If you look at the back of the head on your motor, you will see an externally visible tube, through which the water is bypassed to the water exhaust circuit.

When the thermostat opens, water is permitted to flow through the cooling channels that make up the bulk of the cooling circuit. When you are forcing water up through the cooling circuit with a hose or other device, and the thermostat is closed, the water that is exiting the motor is simply doing so through the bypass circuit. Because of this, the test that you are doing, isn't telling you anything other than that part of the circuitry is clear.

I think your problem is in the remaining portion of the cooling system. You probably have a blockage in it somewhere. You could also be leaking water into the combustion chambers due to a warped head and/or bad head gasket.

At this stage, I think I would drop the gearcase again (if its not already off) and remove the cylinder head. From that point, I would force either water or air through all of the passages in both directions, to see if they are clear or not. You may get some junk coming out when you do this, particularly when your are applying water or air pressure opposite the normal direction of flow. You can also look for evidence of bypass on the head gasket at this time.

Take a look at these items and let us know how you make out.

 

[Phree Refill]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

Jay,

Thank you for your response. Unfortunately, I read it about 12 hours to late. I put the engine completely back together last night. So to do your test i'll have to pull the power head again.

Since I assumed all the passages were clear, I was gonna give it another go in the water barrel. I did find that the little plastic knob that controls the lean/rich valve on the carburetor is stripped. So when you turn it to adjust the fuel mix, it does nothing. This lead me to believe that is is possible that this valve could have been stuck in a full-lean position and, not knowing that this knob was stripped, one would naturally turn the knob to make the fuel a little richer when the engine wasn't running so well or heating up but unbeknownst to them, they weren't actually changing the lean/rich mixture at all because this knob is stripped.

So I was going to give the engine another try and just turn that valve with a pair of pliers. I also made sure I filled the water barrel up plenty. This time I filled it so that water was almost halfway up the driveshaft housing. Started pulling the recoil starter string and almost had the engine firing up and then my recoil starter took a sh*t on me. Evidentally when I put the spring back in it, I didn't wind it correctly. So now the little recoil starter is binding up on me and I have to mess with it. I really didn't think there was any other way to wind it then how I did, but I was obviously wrong. At least i don't have to pull the power head or any of that stuff to work on this little starter. If I could somehow put an electric starter on it I would. This pull string is a PITA.

So I'll see if I can get the engine running again to see if I'm still overheating and if I am then I'll look into the bypass passages in the powerhead. I'll check back in as soon as I find something out.

 

[jay_merrill]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

A couple of thoughts -

First, a low speed needle valve that is incorrectly adjusted wouldn't make water stop flowing through the motor. I think you still have a problem in that regard to figure out.

The reason why the knob is stripped is probably because the packing nut is too tight. Back it out just a little. Be very careful not to bung up the end of the needle valve if you use pliers on it. The part number for the knob is 314615 and it costs $5.49. If you have an OMC/BRP dealer nearby, you might want to just replace it rather than risk damaging the needle valve.

You mentioned that the engine "runs like a top" until the water flow shuts down. That leads me to believe that slow speed needle valve is fine. Also, if the motor ran at all, the worst the needle valve could be off is "slightly." While it is true that engines that are run with a lean mixture will run hot, a slightly lean mixture on a 6hp motor being run at idle, isn't going to cause the kind of overheating that lack of water flow will.

At this point, I think you might be better off concentrating on the problem that you know you have, rather than one you think you have, but have no symptoms of. I know that it "inhales" to have to take the motor apart again, but you need to find the source of the water flow problem.


PS: You might get lucky an find out that the blockage is actually in the head, rather than somewhere in the internal water passages.

When you pull your head again, pull the t-stat too. Turn the head around so that the inner side is facing you. Look at the top right portion of the head and you will see an irregular shaped casting void. Directly above that is a hole that goes into the t-stat housing, drectly above where the top of the t-stat sits. That is the passage that allows a little water to flow through the system at all times. You will see that it opens into a passage that has the metered orifice in it.

To the right of the casting hole, there is a hole that is about the same diameter as the head bolt holes. That passage makes a 90 degree turn to the vertical and comes out on the top of the t-stat housing, next to one of the bolt holes. This is where the water flows into the t-stat housing.

Next, look below the casting hole - there is another hole in a u-shaped channel, which runs down into the cooling passage in the head. This hole is the same diameter as the one that is above the casting hole and it opens into the bottom of the t-stat housing. This is the passage that provides water flow to the rest of the cooling system, once the t-stat opens up. Make sure it is clear!

Finally, look at the bottom of the head, just to the right of the bolt hole that is to the bottom, left side of the head. You will see a rectangular hole down in the water passage. That is the bottom of the bypass tube and you can see that the water jacket into which it feeds, is isolated from the remaining water jacket. This gives you a bit of a visual viewpoint on how the system works.

While my main concern in this "PS," is the passage at the u-shaped channel, I would take the opportunity to clean all of the passages. One trick is to buy rifle cleaning gear - there are wire brushes made for that purpose, which are excellent for cleaning scale and other junk out of narrow water passages.

Let me know how you make out.

 

[Phree Refill]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

Wow Jay. Thank you very much. I just started working on outboards about a month ago so I still don't know too much about them. Your post on the path of the water flow in the head is extremely helpful. I much rather work on my motors myself than pay someone else to work on it. Plus this way I get familiar with the different components so that if in the future something does go wrong I will be able to fix it myself, saving time of getting it to the shop and more importantly the money I save working on it myself. Not to mention that sense of satisfaction you get from fixing it yourself.

Before this six horse, I brought a 1948 evinrude sportsman back from the dead. I bought it off a guy non working for cheap and I had that thing completey torn apart in the livingroom of my apartment (needless to say the girlfriend wasn't too happy). I got it put back together and it runs great! It just isn't big enough to push my 12 footer so thats why I bought this 6 horse. I'm strapped for time right now though cause I'm remodeling my boat. I only have till Friday to get it done. Saturday I'm headed down to Dale Hollow Lake in Tennesee for a week of bluegill and red-ear stalking so I gotta get this boat done. On rainy days i'm trying to get this 6 horse up to par so I can use it down there. If I can't get this 6 horse to cool itself I'll have to use my friend's old 3 horse that he has in his rafters.

I'll make sure to check back in once I find something out on this 6 horse. Again thanks so much!

 

[Phree Refill]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

Just thought I'd check back in and give a little update. Don't know if this will tell us anything but figured it may provide a little insight to what might be going on. Since I had already put the engine back together I set it back in the test tank and fired it up again to study how it was acting. When first fired up it imediately blows LOTS of water through. Water just flies out of the exhaust hole on the shaft. Somewhere in the range of 5-10 seconds in though it backs off considerably and just spurts out droplets of water and the engine starts to get really hot. So i shut it down and let it cool off.

I then pulled the thermostat and left the cover off the t-stat housing and fired the engine back up again. Once again, water gushed through the system and squirted out the themostat port like old faithful. Then 5 seconds in all the water pressure disipated and just started trickling into the t-stat housing. So I revved the engine up quickly and the backed it off and when I revved it, water would squirt out again and slowly disipate back to the trickle again.

Like I said. I don't know if any of that resembles symptoms that can pinpoint the problem but I figured I'd share my findings. When I get the time I will pull the head again and try to make for certain that all the passages are clear. One last thought that I forgot to mention earlier was when I had the head off before and my hand sprayer hooked up to it, I noticed one time that when I pumped water through the water intake port on the bottom of the head that it leaked out of one of the tapped bolt holes on the bottom of the head. Could this be the result of a bad seal/gasket in the head somwhere or perhaps a sign of something worse?

 

[tx1961whaler]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

How high up on the leg is the water in the barrel? It needs to be up at least half way the leg. It could be that the pump is full of water just sitting there, then you start the motor and it blasts that water out the t-stat hole. If the water in the barrel is too low, the exhaust blows the water away from the intake and it just sucks air. If the pump is working correctly, it should blow water continuously out of an open thermostat cover.
I have had water pumps give me fits trying to get them sealed down properly. The last memorable one had the stainless plate that was lifted a tiny bit due to a slightly backed out helicoil.

Also remember that you can spin the motor with a socket chucked up with some adapters on an electric drill. Saves your arm, and you can spin it without actually starting the motor

 

[jay_merrill]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

OK, this gives another clue. When you ran the motor with the t-stat cover off, you should have seen a plume coming out of the bolt sized hole, on the port side of the t-stat housing. If you did, and that plume stopped when the motor ran for a few seconds, the problem is between the water intake and that point.

It sounds to me, like you have a piece of junk in the system somewhere that is floating and being sucked up against something, thereby choking off the water flow. This could be happening either before the water pump or after it. If I'm understanding your posts correctly, however, you have already forced water up through the midsection tube with good result, so I'm wondering if the obstruction is below the water pump.

You may need to drop the gear box and remove the water pump assembly, including the base plate. Check the area just below the base plate for junk and then check the water passages to the side intake and the one that is on the bottom, rear portion of the cavitation plate.

In regard to your water problem in one of the threaded holes - are you speaking of the cylinderhead or the powerhead? If you are talking about the threaded holes on the bottom of the powerhead, those are the holes for the mounting bolts that secure the powerhead to the midsection of the motor. If one of those holes has been helicoiled, its quite possible that the hole was drilled into the water jacket while trying to fit the helicoil. If thats the case, about all you can do to fix it, is to fill the bottom of the hole with some epoxy. When you do this, you should be able to smooth the epoxy where it "squirts" out in the water jacket, with a knife blade.

 

[Phree Refill]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

The lower unit is all clear. I cleaned the intake screen that was just below the back of the cavitation plate and the hole that goes up into the water pump housing. Neither was clogged to begin with but I cleaned the scaley build up out of them. I pulled the cylinder head today as well. I didn't find any blockages anywhere. All the passages were open and relatively free of scale or other buildup. So I then pulled the cast cover on the port side of the power head. Basically the same as the cylinder head; no blockages or buildup. I'm really starting to wonder what is going on.

Whaler, I plan on hooking my drill up to spin the motor to test out the water pump the next few times. That is a good idea. You mentioned that I need quite a bit of water in my tank to make my water pump function properly. Spining my motor with a drill would eliminate the theory about the exhaust blowing all the water away from the intake wouldn't it?

So if I spin the motor with a drill and water flows through the system just fine, could it be possible that this whole time the air blowing out the exhaust was causing my intake to suck air?

 

[tx1961whaler]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

Whaler, I plan on hooking my drill up to spin the motor to test out the water pump the next few times. That is a good idea. You mentioned that I need quite a bit of water in my tank to make my water pump function properly. Spining my motor with a drill would eliminate the theory about the exhaust blowing all the water away from the intake wouldn't it?

Yep

So if I spin the motor with a drill and water flows through the system just fine, could it be possible that this whole time the air blowing out the exhaust was causing my intake to suck air?

Yep. I use a large metal trash can. My 6 hp touches the bottom of it when clamped on the side, and I fill the can almost all of the way up to test it. These guys like to be in deep when in a barrel....I have to be real careful when using the can for my 40 hp. I prop it up from underneath as high as I can and keep it filled with a hose when running it.

 

[jay_merrill]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

Although this usually doesn't happen unless you have the motor in gear with a bit of power, its easy to blow enough water out of the barrel to lose suction at the water pump. For this reason, I leave a hose running into the barrel so that it refills as I am running the motor.

If that is what is happening here, I guess we are all going to feel silly!

 

[Phree Refill]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

I am going to try filling up the barrel as much as possible tonight and spin the motor with my drill. If it continually pumps water then I'll try firing it up and seeing if it keeps pumping. I have a quick question though. If in my barrel the exhaust is blowing all the water away from the water intake, who's to say it won't do the exact same thing while I'm out on the lake?

 

[jay_merrill]

Re: 1976 Johnson 6 Horse Cooling System Conundrum

I've never had problems with exhaust blowing water away from an intake - in a barrel or otherwise. If that is happening, you must be using a very small barrel. I would use at least a 30 gallon trash can. If you use an old one, make sure you clean any debris out of it.