Overheating Johnson 115

[bobsquatch]

My 1973 Johnson 115ESL73 115HP has just started overheating under load. This just started 2 days ago after a day of fun tubing/cruising with the kids. All good all day long. The last 30 min of the day I was making a sustained high speed run near maximum rpm for a little thrill as we ended the day. As we made our final turn toward home dock my temp alarm went off and I shut down to idle then off within 15 seconds. I checked the intake for blockage and pulled the cover and confirmed the motor was hot. No blockage on intake but steam+alarm on restart so I called for a tow. Yesterday I ran on muffs with a temp gun and all is well so I decarbed the engine with seafoam per instructions on this site and launched again. All good at idle but under any load it gets hot fast and alarm goes off. I let it sit for 10 min then restart with alarm screaming but I see enough water spitting out the relief ports to let it idle the 30 seconds it takes to cool off and silence the alarm. I idled around long enough to burn my 1 gallon of fuel with the seafoam in it and took her home. I just replaced the intake screen, water pump impeller, shift shaft oring seal and lower unit oil. I went on a 30 mile open ocean sea trial to confirm repairs with no issues. I am thinking thermostat blockage as the thermostat appears to be working but not flowing enough water for heavy loads. Any thoughts?

 

[bobsquatch]

I have a tell tale kit and a head gasket on hand so I will pull the starboard side head and check for obstructions and water circulation stop position while I install the tell tale. I will also pull the thermostat to test and look for obstructions. Should I use 765-1210 napa/permatex aviation liquid gasket sealant on my head bolts like on submerged parts or not? The book says use omc sealing compound 317201 lightly on the head gaskets. Really? I have never heard of coating a head gasket. Is the napa 765-1210 a suitable substitute?

 

[Bosunsmate]

Might be a deformed check valve, also about the gasket see if your replacement one has any already on it, I dont bother with the headbolts, i just clean the threads and dip them in light car oil

 

[ondarvr]

When you pull the heads off check the deflectors, they can swell and block flow.

 

[bobsquatch]

Might be a deformed check valve, also about the gasket see if your replacement one has any already on it, I dont bother with the headbolts, i just clean the threads and dip them in light car oil

Thank you I will check the gasket when I pull the head off also what about aluminum based antiseize as opposed to motor oil for the head studs?

 

[bobsquatch]

When you pull the heads off check the deflectors, they can swell and block flow.

I will certainly do that. On that note is there a source for those where they are not $15 plus a piece? I have not pulled the head yet therefore I have never seen one but I can't imagine they would be too difficult to manufacture oneself. I am ordering a second head gasket so I can look at both cylinder banks and see if there are any obstructions or swollen diverters I did have a broken intake screen last month that I have repaired and had no problems with since however things are known to linger around a bit before they start causing problems who knows what I will find when I get in there.

 

[ondarvr]

You can match up the diverters with fuel line, nothing speacial.

 

[bobsquatch]

You can match up the diverters with fuel line, nothing speacial.

I was thinking along those lines. Can anyone argue with that?

 

[bobsquatch]

I got the thermostat apart. It is a single unit (I thought it had two). I did find a little glob of what appears to be the liquid gasket sealant I used for the shift rod cover gasket and lower unit mounting bolts on the starboard nipple of the thermostat housing. The Vernatherm works on the stove top and the assembly looked pretty clean. I thought the vernatherm valve was wedged (which would explain the over heating) but I did not realize how substantial the spring is so it may have moved with more effort. I will clean all the pieces and reassemble. Any suggestions for cleaning and lubrication for reassembly? I am thinking of sanding down the imperfections in both plastic valves. Any thoughts on that? I will pull the starboard head tomorrow and look for gasket sealer in the water passages. While there I will inspect/replace water diverters as needed. I will also install the tell tale fittings and plumbing.

 

[bobsquatch]

I am also thinking I should run the engine without the thermostat housing installed on muffs for about 10-15 seconds to see if any debris comes out the now unobstructed ports. Shouldn't hurt anything running that briefly without cooling the cylinders. Any thoughts?

 

[Bosunsmate]

Thank you I will check the gasket when I pull the head off also what about aluminum based antiseize as opposed to motor oil for the head studs?

Sure thatd be good, im just too cheap to buy that

 

[Bosunsmate]

I was thinking along those lines. Can anyone argue with that?

Nope id only argue for it. Its a good idea to do them all they get brittle and deteriorate

 

[Bosunsmate]

I am also thinking I should run the engine without the thermostat housing installed on muffs for about 10-15 seconds to see if any debris comes out the now unobstructed ports. Shouldn't hurt anything running that briefly without cooling the cylinders. Any thoughts?

go for it

 

[bobsquatch]

So today I learned something about my cooling system in that it flows in the opposite direction that I thought it did. The water flows from the intake up through the cylinder cooling passages out through the head and into the thermostat and from there down to the exhaust so I could have Ran it forever on the muffs with the hoses disconnected from the thermostat and everything would stay cool. The good news is the system appears to be clean with no debris to b found.

 

[bobsquatch]

I also pulled the starboard side head to find the diverters in place and looking good as well as clean water passages and crystal-clear honework from a nearly brand-new engine rebuild that isn't even broken in yet. There could yet be an obstruction in the port side cooling passages and I will inspect them when I get another head gasket but I believe I may have found the problem with my cooling system elsewhere. I believe the front of the vernatherm valve was wedged and that's why I could not move it with my finger I finally broke free and it wedged again but I managed to free it and it seems OK now even though it was clean and in structurally perfect condition I suspect this is the problem.

 

[bobsquatch]

So today I installed the tell tale kit on top of my #1 cylinder and a new Vernatherm with a new head gasket. I ran to check for leaks and found none. The tell tale stream was long in coming. Maybe 15-20 seconds then it was unsteady sort of 80% on 20% off and not super powerful at idle. I am guessing the impeller spun out of the key or the housing cracked. I do however have strong flow at the drain holes and lower exhaust ports and my head temperatures were only 125 port and 130 starboard. Any thoughts before I drop the lower unit again?

 

[bobsquatch]

After thinking about it the stream was probably closer to >95% on <5% off with a weakish stream.

 

[interalian]

By tapping into the water jacket at the top of #1, you should have full pump pressure available - 10psi at least. If you're getting air but the heads/crank case aren't overheating that's a mystery.

 

[bobsquatch]

Ok so i dropped the lower and I am glad I decided not to launch. I found the guide tubes off the water pump coupling flange item # 84 in the following link http://www.marineengine.com/parts/j...&manufacturer=Johnson&section=Exhaust+Housing
It would appear that my sustained high speed run made enough pressure to pop the tubes off. With them disconnected high volume water escaping at every relief is the only pressure left to get to the upper engine and is in sufficient under any load. I do not remember there ever being a grommet for the tubes and the parts breakdown does not show them. I am going to re seat them but does anyone have a trick to keep them in place?

 

[bobsquatch]

Well after further investigation I am wrong again. Tubes are just guides and hold no pressure. It was weighing on me to check the impeller key since I had the lower off. It was hard to remove until I was able to spin it on the shaft. The cheap impeller core is made of plastic and the key spun through it. I fortunately have a complete rebuild kit p/n 0439140 on hand with a good ole American made metal core. I will be installing the housing, wear plate and seals but the kit comes with an oring that I do not see where it goes. The only thing I can think of is on the top of the drive shaft below the splines. Is one supposed to go there?