1967 80HP Johnson overheat problem (Solved!)

[Aratsman]

I am having a heck of a time with this motor. I have searched the forum and have read every post concerning overheating. I am at a loss now. I have replaced and tested everything I can think of and it still overheats. List of what I have done already.

1. Replaced Impeller. Still overheats.
2. Checked thermostat. It appeared to be stuck, got it freed up and reinstalled. Still overheats.
3. Dropped lower and checked pump in tank with drill. Appears to be working, not a guyser but still pumping water. Still overheats.
4. Pulled exhaust housing because the tube on the pressure side would turn and had play in it and the return did not. Resealed everything reassembled. Still overheats.
5. Hooked a garden hose directly to the pressure tube and ran motor. Good flow out of the thermostat housing on both the pressure and return sides. With thermostat installed, after a min or so began to get flow out of return tube. Reassembled lower and ran, still overheats.
6. Pulled thermostat. Still overheats.
7. Pulled hoses off bottom of heads, I do have water flow, but it is not like turning on a garden hose.

With all that said, I am getting a mist out of the exhaust hole and it does appear to get stronger as the engine heats up. I have been careful to make sure the pipes are aligned and in the grommets in the pump during reassembly. I have tried two impellers, checked every pipe. I did notice one thing about the pressure tube that I have not read anything about. Just before the pipe goes through the grommet in the exhaust housing, there are two holes about 1/32" in diameter and are rotated 90 degrees from each other. They are about 4 inches from the water pump. What are these for? Some sort of pressure relief? It would seem to me that these holes would decrease pressure to the block. They appear to be drilled into the pipe and not damage. I also would like to know what people have found for pressure out of the pump when testing off the engine with a drill. I have tried everything I can think of to get this motor to not overheat. I sure would like to use this engine. Getting around on a 9.9 is getting old.

 

[Sixmark]

Re: 1967 80HP Johnson overheat problem

Re: 1967 80HP Johnson overheat problem

Right off the top of my head, there are two relatively simple things you can do:

1. Replace the thermostat, once a t-stat becomes stuck, it really should not be trusted to work properly afterward.

2. Do a compression test, this would be a very good indicator to let you know if you have a bad head gasket.

Also, how did you come to the conclusion of an overheat problem? Are you relying on a reading from a temp gauge or were there other indications of an overheat that you did not mention? You should be able to put your hand on the head of the motor for a few seconds without trouble.

 

[Aratsman]

Re: 1967 80HP Johnson overheat problem

Re: 1967 80HP Johnson overheat problem

Overheat light, both heads are hot to touch, cannot keep hand on head for more than 2 secs without a trip to the burn unit, definately alot hotter than my 9.9 at operating temp. I am going to replace the thermostat, just wanted to get it to operate without removing it, which I ended up doing anyway. Compression check still needs to be done. Will get to that tomorrow.

 

[Sixmark]

Re: 1967 80HP Johnson overheat problem

Re: 1967 80HP Johnson overheat problem

Be sure when doing the compression test to ground the spark plug lead when cranking the motor to avoid damaging the ignition system.

 

[Aratsman]

Re: 1967 80HP Johnson overheat problem

Re: 1967 80HP Johnson overheat problem

Yup. I suspect the water pump is not pumping enough water for some reason.

 

[F_R]

Re: 1967 80HP Johnson overheat problem

Re: 1967 80HP Johnson overheat problem

The holes in the water tube are to cool the area so the electric shift cable doesn't burn up (if equipped). Don't worry, that is only the proverbial drop in the bucket, compared to the total water pumped.

The holes should only be in the UP pipe, NO holes in the return pipe.

I am wondering, are you running that thing on a boat in the lake? How hot is "overheat"? Are all the parts in the thermostat housing?

It would sound from your description that it is working. It should blow a mist when less than thermostat opening temperature and a heavier spray when open. The 'stat is constantly sampling water temp and opening and closing as required to maintain proper operating temperature.

If it truly is overheating, on a boat, in the lake, and everything is as it should be, my guess would be that there is and exhaust leak into the cooling system.

You haven't dinked around with the water passages in the powerhead adapter, have you? That small hole on one side is supposed to be small.

 

[Aratsman]

Re: 1967 80HP Johnson overheat problem

Re: 1967 80HP Johnson overheat problem

No I haven't modified anything with the system. It is an electramatic so that would explain the holes. All parts are in the thermostat housing (pressure relief valve and spring along with the thermostat and spring). The engine is mounted on the boat, in a large barrel. Water level is well above the LU and exhaust meeting area. I have changed the LU as the original went bad (clutches went out). The replacement LU is off a working '68 85HP and is a 100LU. I guess if your hunch is right, I'm looking for a blown head gasket allowing compressed (pre or post fire) gases through and into the water jacket. Need to do a compression test first thing this morning to rule that out.

 

[yorab]

Re: 1967 80HP Johnson overheat problem

Re: 1967 80HP Johnson overheat problem

There are also a few seals in the lower unit that prevent exhaust gases from entering the cooling system. The main one is a felt-like donut seal that seats around the top of the impeller housing. Is that in place?

 

[Aratsman]

Re: 1967 80HP Johnson overheat problem

Re: 1967 80HP Johnson overheat problem

No I did see that was not there as I inspected that area looking for a leak around the driveshaft going into the waterpump. No felt but the rubber seal is there and working fine. I'll check that out. Taking it down to a friends shop in the morning to do the compression check. He seems to think also along the lines of a head gasket.

 

[yorab]

Re: 1967 80HP Johnson overheat problem

Re: 1967 80HP Johnson overheat problem

Even though the rubber-lip seal is in place in the impeller housing, the donut seal must also be there, at least that true for the 1963 75hp. Your design may be different, but I don't believe so.

 

[Aratsman]

Re: 1967 80HP Johnson overheat problem

Re: 1967 80HP Johnson overheat problem

I saw that felt washer in another post. I'll shove one in there tomorrow. It can't hurt it to have one in there I imagine.

 

[yorab]

Re: 1967 80HP Johnson overheat problem

Re: 1967 80HP Johnson overheat problem

From the official 1964 75hp Starflite Factory Service Manual:

"It is especially important that the impeller housing seal ring fit properly to prevent exhaust gases from feeding back into the intake manifold through the driveshaft housing."


It's also important the the water tube grommets or bushing/o-ring combination be in good shape. The inlet and outlet pipes each have these grommets. Again, from the FSM:

"Install new grommet in impeller housing to prevent exhaust gases from getting into the cooling system, causing overheating and pre-ignition."

 

[Aratsman]

Re: 1967 80HP Johnson overheat problem

Re: 1967 80HP Johnson overheat problem

Well, the compression test yielded nothing. 110 PSI on all but cylinder 4 which was 100 PSI. May still pull the head a replace the gasket anyway just to rule that out, but I'm doubting that is the problem.

 

[Aratsman]

Re: 1967 80HP Johnson overheat problem (Solved!)

Found the problem. The tubes were 1/2" too short and not fully seating in the grommets in the W/P. Cut the tubes back around 3" and soldered a coupler and new 1/2" copper pipe on. New ventatherm and presto! Good flow and no overheat. Didn't think s 1/2" would make that much of a difference, but I guess it does. Now off to replace some rubber hoses. Ran it on the lake and starving for fuel. Found the pressure line into the fuel pump was cracked. New line tomorrow and I hope she runs great!

 

[yorab]

Re: 1967 80HP Johnson overheat problem (Solved!)

Thanks for posting the resolution. Should help others who search the forums for the same problem.

 

[Aratsman]

Re: 1967 80HP Johnson overheat problem (Solved!)

Too many times I have seen people on here post they "will post how it runs tomorrow" and it never happens. I am a firm believer in how much this forum helps people, I know it has really been a godsend for me. If it is fixed, people should know what you did to fix it so others can benefit from the knowledge also.

 

[yorab]

Re: 1967 80HP Johnson overheat problem (Solved!)

By the way, any idea why the tubes were too short?

 

[Aratsman]

Re: 1967 80HP Johnson overheat problem (Solved!)

Yes. I switched from a 80HP electric lower to a 100HP lower. The 80HP tubes were too long and I had to cut them back. Measured twice, cut once, everything looked good, but I must have been a little too short. I thought I had left more than enough. I would have rather cut more off if I had to, than have to go through adding more back. A 1/2 inch does make a difference! Got it out yesterday, had carb problems and couldn't get it to plane. Finally got it to run halfway correct and got the boat up to 27MPH. Still more work to do, but I am happy with the progress.