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1979 85 HP Johnson temp switch (Thermo switch)

P

propshaft

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I recently dropped a 1979 85 HP on my transom, (15 foot tri hull that had a 70 merc) It runs great but the alarm in the shifter control started buzzing spuraticly the other day while running it around 4500 rpm for a while. I checked the engine temp all over with an IR temp gun and it was barley over 100 degrees everywhere I checked. This led me to believe the thermo switch might be bad. It only has one thermo switch on one head and the other head the thermo switch has been removed by previous owner. I checked the lead from the disconnected thermo and found a little of the metal knife connection was exposed from its cover. Its possible it was grounding to the block causing the spuratic buzzer. Now after looking for a new thermo switch I see they are NLA. I have a newer 110 parts motor that has both thermo switches (same part # also) I can rob but they only have a single leed wire. The part # I looked up that is NLA has 2 leeds. Did the original thermo have 1 or 2 leeds. 1 leed wire is a ground on the part# I looked up and the other leed (knife connector) feeds back to the control box. But the one in the 85 hp and the 110 have only 1 leed wire. I can only assume the thermo is grounded to the head on the ones in my motors. Any knowledge of these thermo switches is much appreciated. It would be nice to get a warning buzzer before overheating or seizing the old 85hp since its a great runner.
 
those thermo senders are crap full stop, if and when they work, the are far too late to be of any use.
by the time the motor is hot enough for those to send signal to control box the motor is a around 180 to 190deg, thats is far too hot and damage has been done .

get a much more modern temp set up and use a gauge or gauges.
 
Well. I found somebody that agrees with me. My experience is that they might work if the heat situation comes on slowly. But if it is a sudden overheat condition such as a spun water pump, the powerhead will destroy itself long before the horn blows---if it blows at all.

Gauges aren't much better. Who goes around with their eyes glued to the gauge? I suppose the best is a combination of both. But really, the best is just make sure you have a good, fresh water pump impeller in there, and relax a bit.
 
I tend to look back at the stream coming out the pisser periodically. Mostly pulling tubes and skiers so Im glancing back quite a bit anyway. Its pumping water just fine and runs great. Just kinda dumbfounded when the alarm went off and after checking temps all over with IR temp gauge. Next time I go out I'll check connections again. I did pull a thermo switch off the 110 hp parts motor I have so I might replace the missing one. I picked this 85 HP motor up last year for $200 and had to replace a power pack to get it going. $30 on flea bay for a used one. Compression is 120 on all 4 cylinders. Heck of a deal! I dont have a clue when the impeller was last changed but it was pumping strong. Might go ahead and replace it just for peace of mind. Thanks for the input.
 
replacing the impeller is good for many reasons, obviously for the water to be coming through nice.
but a big thing is that the leg comes off once a year means it dont weld itself on!!!
so many people have main driveshaft welded itself to the crank an then its scrap because leg has not been dropped for years.
when putting it back only grease the sides of the splines, and put plenty of dish soap on the impeller for lubrication on first start up with new impeller.
 
My plan is to run this 85hp the rest of the summer and tear it apart in the fall and replace the impeller and put a seal kit in the lower unit. Its running strong and water pump is doing its job. Just preventative maintenance after this summer. I live along the Potomac river and keep a dock in, so the boats and jet skis stay in all summer. The current project is a 26 foot pontoon with a 40 evinrude. Its getting the impeller and seal kit next week while I'm off work. Then its getting dumped in with the rest of the fleet. Love boating and bought my first boat when I was 17, now 52 and still at it every year! Thanks for the input!
 
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