'79 15 HP Johnson Water Circ. Question- Overheating

[kahuner]

I have just replaced the water pump impeller and did some other maintenance on the motor over the winter. I started the motor (for the first time after servicing) on the back of my boat at the launching ramp.

Water discharge was excellent out of the 2 exhaust' water ports just below the lower cowling out of the exhaust housing but weak out of the tattle tale port. Ran the motor on the lake, seemed to run fine but noticed that the water coming out of the 2 ports was always cold.

Later that day, noticed that there was no water coming out of the tattle-tale port. Water discharge out of the 2 exhaust housing ports is strong. Discovered that the tattle-tale line was clogged with mud/ weeds. Cleared the line out but still no water discharge and motor runs hot while the water discharge from the 2 ports is cold.

My question is: could the thermostat be stuck, clogged internal water passage? If water is coming out of the 2 ports in the exhaust housing, the water tube must be aligned correctly, right?

 

[bktheking]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

They should run warm, 140F do be exact. Tstat could be stuck or they go the other way and break and they run cold. The telltale is before the thermostat and has nothing to do with water flow. If the water is coming out the exhaust ports that means stat is working, could be a blockage but you need to determine "hot" vs "normal".

 

[kahuner]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

bktheking,

Glad you're online to help! I almost noted in my original post: "bktheking, where are you?" I always appreciate your help!

How hot is hot? I knew somebody would ask that! I'm in central MN at my fishing camp and did'nt pack my temp gun. But I can tell you, based on my feel of the head, it''s way over 140*. Can't hold my hand on the head for 5 seconds.

When I first discovered the water temp problem, the motor smelled hot. Not enough to discolor the head, but hot. It stopped running at an idle. That's when I started looking at possible overheating problems. Let it cool down and it started right back up. Secondly, the water out of the exhaust ports is always cold. If the tstat was working, wouldn't the water, after full warm-up and a short run, turn warm?

And just to be clear, are we in agreement that the water tube is probably lined-up because there is excellent wtaer flow from the exhuast ports?

 

[bktheking]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

Yes I think you have the tube in. If the water is coming out of the exhaust then the stat is opening, it should be the second last point of exit, hub being the last. But the water shouldn't be cold, from the telltale yes, warm out the exhaust housing. You either have a blockage somewhere or the stat is weak. The stat housing can be pulled without removal of the hood latch, I did it 2 days ago. Test your stat in boiling water to make sure it's up to spec.

 

[kahuner]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

I think I've found the problem.

Removed the head and found the head gasket has a witness line (wet) between the inner head gasket surface and block on the lower cylinder. This is right next to the tstat water jacket. Could've been blowing compression into the water jacket at the tstat and preventing water circulation.

During the winter I replaced the lower crankcase seal. It was shot. Now that the lower cylinder is producing power, the next weakest link was the head gasket.

Sound right?

 

[oldcat]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

If something is amiss between the water pump and the crankcase, such as a broken, leaking or unaligned transfer tube or a completely shot grommet in the adapter plate then cold water could fill up the mid and then exit out through the exhaust relief.

Telltale would be weak/nonexistent as well.

 

[bktheking]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

While you have the head off check the tstat and yes could be, did you take compression reading before you removed the head?

 

[kahuner]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

Compression before was 100# on the top, I had to pull one extra time to get 80# on the lower. 4~5 pulls.

Just ran it on the muff. The tattle-tale does work better (there is a constant flow) but I still think it should be stronger. Takes about a minute to have water come out the 2 ports in the housing from start-up. Water out of the tattle-tale is warm, water out of the housing is cold.

This takes all of my inner-strength to admit this but the head feels just as hot as it did on the lake. So I either:

1. did all of this work for nothing although the head gasket was leaking
2. it's the water tube causing this and Gawd I hate the thought of removing the lower unit!!! Or
3. 140* to the touch is hotter than I thought and it was just some mud in the tattle-tale line!

 

[kahuner]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

Oldcat;

During the winter I serviced the steering column and lower vibration mounts which required removing the powerhead. While it was off I replaced the water tube grommet in the exhaust tube and re-installed the water tube. Rebuilt the lower unit and water pump. So both grommets were new.

I struggled re-installing the lower unit aligning everything! The shift linkage is a giagantic PITA! However, each time that I had to start over, I always looked at the water tube grommet on the water pump and never did it look deformed. The water tube itself is contained in a hole on the exhaust tube which helps realignment.

I'm not going to say that the water tube isn't misaligned but I doubt it.

BTW, I installed a new tstat, water passages looked normal. Not a lot of sand, silt sedement.

 

[Rick.]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

Based on what you've told us I would pull the leg and make certain the water tube is dead centered in the water pump grommet. I always grease the rubber good to help it slip into place. It is a PITA but the more you do it the easier it gets. Rick.

 

[kahuner]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

Dropping the lower unit is my next step.

I'm reluctant to do it but it's the only way to have peace-of-mind.

When I remove the lower unit, inspecting the water tube grommet on the top of the water pump housing is the only way to determine if it was misaligned before right? The obvious next question is "how to improve my chances of success this time after reassembly?" For the life of me I can't imagine how OMC assembled these motors in production!!!

I did grease the water tube before, but like I said earlier, it took me at least five tries before (to install the lower unit) and each time I did it, the water tube grommet looked fine.

Since my last reply I tested the motor at the boat launch. The amount of water from the tattle-tail was about the same but warm, sometimes hot. Water from the 2 exhaust ports was warm sometimes, but never hot. I'm thinking that may have been due to being mixed with the exhaust gases.

When the lower unit is off, I might as well make-up a fitting from a hose to the water tube itself and evaluate the flow of water.

I'll post an update tomorrow.

 

[Rick.]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

That is an excellent idea. A word of caution though. I have been doing that for some time now but last year I gave the water tube full city (town) pressure and caused a leak in my exhaust plate. I still think it is a good way to flush an engine but careful with the pressure. I had the motor tilted up and tell tale water was shooting 30 feet across the shop which was a really dumb thing to do. I would also recommend pulling the head so water can purge anything up there as well. Rick.

 

[kahuner]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

Dropped the lower unit this morning. *wiping the tears from my eyes 'cause I can't see my 'puter screen*

Water tube grommet was not aligned onto the water tube.

Found significant water/gear oil mix in the exhaust chamber portion of the lower unit, just rearward of the water pump housing section. Also present in the 5" extention and in the exhaust housing mid-section itself. Looks like gear lube/water mixed.

No oil resiue in the shift linkage area or on the top of the water pump. The lower unit was just rebuilt with all new seals. Lower unit oil looked fine when I drained it.

Where would the oil be coming from?

Boy this frustrating!!

 

[bktheking]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

Milky white or grey/brown watery looking, remember the headgasket was suspect, could be oil/water mix coming from the powerhead down.

 

[kahuner]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

bktheking,

They must've called you "lettuce" in high school eh? You were the one with a "head" on your shoulders!!

I totally forgot about the head gasket leak causing the oily residue!! Totally forgot!! However;

I'm going to take the motor to the local dealer here to have the lower unit pressure tested just to make sure and they will re-install the lower unit. My confidence is gone!! I don't have the little Mighty Mac to pressure test and I don't want to worry about possibly missing the water tube alignment again.

Thanks to both you and the others for your help! Next time I'll try to better match my skill level with the job at hand.

 

[bktheking]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

Dropped the lower unit this morning. *wiping the tears from my eyes 'cause I can't see my 'puter screen*

Water tube grommet was not aligned onto the water tube.

Was the grommet folded over, it's the only time i've seen an issue besides the grommet being loose from stretching over time. If it weren't in the tube there would be no water flow. I noticed you only did the impeller, the grommet at the top of the pump housing is equally important in cooling as they tend to fold over or become loose over time, it might not hurt to replace it before putting the lower unit back on.

 

[bktheking]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

bktheking,

They must've called you "lettuce" in high school eh? You were the one with a "head" on your shoulders!!

Believe it or not I was a C+(D+) student who only did well in Computer and Shop class. I skipped school around 1/2 my highschool years. Then went to college and got a diploma in Computer and Electronics Engineering and graduated with honors, go figure. It must have been being in my dads garage as a kid from age 5 on and asking too many questions and learning every curse word in the book LOL. But i've always been a tinkerer and I've found that outboards are one of the most amazing technological marvel's of the 21st century and I love boating so the 2 go hand in hand. And I'm still learning, guys like Ezeke, F_R and Joe Reeves were OMC tech's, I can't touch their knowledge when it comes to the OMC knowhow.

 

[the machinist]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

A suggestion would be to purchase a new water pump outlet grommet. The new ones are slightly taller & have more of a upper taper to better self-align the tube when reinstalling the lower unit. This taller grommet also helps when reassembly because the tube & the shifting rod now go in at different times instead of almost at the same time.

 

[kahuner]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

bktheking aka Lettuce and the machinist;

I hate typing and therefore from time-to-time abbreviate alittle too much by not telling every little detail. My bad!

When I rebuilt the lower unit and water pump, everything was new including the water tube grommet, impeller. But during installation, the tube dislodged the grommet inspite of the improved design. The 2 little tabs were in the holes to help hold in place. (that didn't get by me!!) By the looks of the grommet, the tube grabbed one of the sides of the grommet and drove it down into the neck of the water pump housing.

There was water coming out of the 2 exhaust ports, in fact I would say it was substantial. But not very strong out of the tattle-tail. Tattle-tail water did get warm, sometimes hot, which I thought was a bad sign since I've been told on this thread that it's always cold.

Here's an update on the oily residue. The dealer here (in a little small town in central MN with a fantastic reputation) looked at the lower unit and the 5" extention and said: "That's not lower unit oil, it's residue from the gas/ oil mix. We see a lot of this on 15 HP motors." Maybe the head gasket leak added to the amount present but still to his point, ya might want to make a mental note about that!

I'm using Johnson oil XD 50.

They're going to pressure test just to make sure there's no leaks and reinstall the lower unit. If there's no lower unit leaks, it's 1/2 hr labor to test and reinstall L/U.

"$45 bucks and I'm outta this mess!!" I don't have problems really; just expenses!!

Let's see now; where did I put that Vodka bottle?

 

[bktheking]

Re: '79 15 HP Johnson Water Circ. Question- Overheating

Well that's good news, I guess it's just the attention to detail upon reassembly. When I reinstall I get down on the ground and lookup to make sure the tube it going in and I tend to spread the coupler open on the shift rod to make things easier to reattach the shift rod.