1981 johnson 140 v4 overheating

I have a 1981 Johnson 140 that one side of the engine is getting hot and the other is cold. I have replaced the impeller and put new thermostats in and still no change get so hot you can't touch head or engine. Remove both thermostats and engine runs cool like it should. Any body know where to start to fix the over heating problem?

Re: 1981 johnson 140 v4 overheating

Reinstall the thermostats, remove the cylinder heads and check the water deflectors.

(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.

Re: 1981 johnson 140 v4 overheating

I replaced the deflectors and still gets hot on the same side. I remove the thermostats and the boat runs cool. test thermostats in boiling water they both open like normal. reinstalled thermostats boat runs hot on one side. I just don't under stand there has to be something I'm missing. any one have any ideas???

Re: 1981 johnson 140 v4 overheating

Did you ever take some readings on it with a temp gun ??

Re: 1981 johnson 140 v4 overheating

Silly question mebbe, but are the relief valves/springs installed properly?

Re: 1981 johnson 140 v4 overheating

Is the water pump indicator stream hot? Which side is hot / cold? You could have exhaust gases leaking into the water jacket. That would cause overheating even though everything else looks and checks ok.

Re: 1981 johnson 140 v4 overheating

jeff1163 said:

I replaced the deflectors and still gets hot on the same side. I remove the thermostats and the boat runs cool. test thermostats in boiling water they both open like normal. reinstalled thermostats boat runs hot on one side. I just don't under stand there has to be something I'm missing. any one have any ideas???

Click to expand...

I had this same issue on my 1996 Johnson 88 SPL. Starting it cold, the right bank would overheat and the left bank would stay cold and the center plate would get hot. On the thermostat block (black plastic piece) there is a pin hole in the middle of the block. This pin hole lets water escape from the thermostat housing, allowing the warm water to enter from the cylinders and begin to open the thermostats. If this pin hole becomes clogged, it will not allow this initial water circulation, water in the cylinder jackets gets hotter and it overheats.

My solution was to drill the pin hole out with a 1/8" drill bit. This solved my overheating issue. If you don't want to experiment on your original thermostat housing, there are usually used parts available on Ebay. This part is common to many years and models. Good Luck

Re: 1981 johnson 140 v4 overheating

no I did not take any readings with a temp gun just with hands. no longer than I let it run the right side would blister your finger if you held it on the head long enough. the stream coming out the pee hole is cold. I will have to check the hole in thermostat block I never payed much attention to see a little hole in center. and the relief valves are in correctly.

Re: 1981 johnson 140 v4 overheating

Dargel is correct. The two pinholes in the valve body in the thermostat housing must be open. They let hot water bleed to the back of each stat so that it will heat up and open. Easy for these pinholes to get cruded up over the years. If one pinhole plugs up the engine will overheat on one side.