One side heating up. 78 Johnson

[Vere]

Hi

Latest issue in my quest to understand my motor more.

78 115hp Johnson. Noticed today while trying to fix other stuff that the left side black pipe at rear of engine was extremely hot to touch after 4 or 5 mins running (out of water but with water ear muffs on), whilst right side was fine. Any ideas ?

I also originally thought I had no solenoid, but it appears I do. Did check and tested 3.4 Ohms (manual said should be 4), is that ok ?

 

[Joe Reeves]

Re: One side heating up. 78 Johnson

Overheating = Thermostat (you have two) failure or water deflector trouble as follows.

Solenoid..... what solenoid?

(Water Deflectors)
(J. Reeves)

Water deflectors are actually lengths of 3/8" outside diameter rubber hose, installed between the top cylinder and any cylinder beneath it, and also between the bottom cylinder and the block. The purpose of the deflectors is to have the water follow a definite path around the cylinder walls. Unfortunately the deflectors between the cylinders will at times swell sideways due to either a previous bad overheating problem, or simply due to age and salt corrosion. This causes a water flow restriction which usually allows the water to cool sufficently at low rpms but not at the higher rpms.

This hose material can be purchased reasonably at any automotive parts type store if you care to make your own, or you can purchase individual deflectors at any Evinrude/Johnson dealership at a somewhat higher cost.

Removing and installing them can be a hassle at times, but not always. I use a sharply pointed scribe with about 1/4" of the tip bent at a right angle whereas I can reach in, jab the tip sideways into the rubber, then yank it out. It's necessary to clean the seating surfaces where the ruber contacts the block with a small rat tail file to eliminate salt deposits etc. When installing the new rubber deflector, coat the deflector and the metal surfaces with WD40 which will act as lubrication to allow it to go in as easily as possible.

Make sure that you insert something into that deflector area before cutting and installing the deflectors if you make your own so that you will be certain that they are the right length and also that they will be seated properly. Usually a very small amount will be left extending about the block sealing area..... simply cut the excess off with a single edge razor blade.

 

[emdsapmgr]

Re: One side heating up. 78 Johnson

The engine has two thermostats in the thermostat housing, one for each side of the block. If the port stat sticks shut, it will not let any water circulate through that side of the block and you will get an overheat at idle on that side. If you go into the housing, you might as well replace both at the same time.

 

[Vere]

Re: One side heating up. 78 Johnson

Thanks for the advice. Im going to try doing this shortly, mainly as I actually want to understand what Im doing rather than simply spending the bucks on a repair shop. Would love to understand the motor more, though as someone pointed out, by the time I do I?ll be ready to upgrade it !

On a parts question, my motor is 115ETL78C. Looking on the Johnson parts website this model number isnt there (they have 3 similar ones but not mine). Would parts such as thermostats be fairly interchangeable, and also choke solenoid (see below) ? Live in Spain and old motors for breaking seem scarce, so guess will have to try ebay etc and pay shipping and don?t want to go getting a piece that wont fit....

With the solenoid, I mentioned it in another post also, but it seems to me that Im missing the choke solenoid. Certainly theres a gap that looks like thats where one should be, and only option at the moment is manual choke. Empty bracket basically is just above air silencer unit, front of the motor opposite side to manual choke (looking at motor from inside boat). If it is missing, could also explain the switch next to starter in cabin that appears to do nothing....

 

[emdsapmgr]

Re: One side heating up. 78 Johnson

The stats for this engine are common across all models with the double thermostat housing. You'll need to check the factory parts list on the choke solenoid, as there are different ones for different applications.

 

[kameika]

Re: One side heating up. 78 Johnson

I had a similar problem -- haunted me all year last. I'd run at 3/4 throttle--never a problem (though I noticed SB cylinder head was hotter than the Port side)..

At WOT, I'd get the "oh shxx, slow down" overheat alarm.

Tested the thermostats in a pan of water. Wonderful. Cleaned the housings, perfect.

Replaced, then re-inspected the water pump. Wonderful.

Problem persisted.

Then. I decided to buy new thermostats, despite the test in the pan of water. Problem solved.


Moral of the story? Thermostats do not die suddenly. They die slowly. Instead of opening full stroke (at full temperature), they will open 3/4 the way. Or less.

Now you have a problem at highest load.

The suggestion? When in doubt, change the thermostats. $35 for two. What a bargain.

-Ken