Thermostat replacement on '79 Johnson

[blackwaterstout]

Just realized that I should have replaced the thermostat on my '79 Johnson 25 when I replaced the water pump. But after looking at the engine diagram I'm a little confused as to how it's done. I have a Seloc manual thats not real helpful. It appears I have to take the back of the crankcase off to access the thermostat. Is this something that could get me into trouble? Will I need to replace the crankcase gasket at the same time? <br /><br />The reason I think I need to replace the thermostat is because my engine feels hotter than I think it should. I can't hold my hand on it for an extended period. And it doesn't have an overheating horn. <br /><br />Anyone know where I can find actual pictures of the thermostat installation on a johnson engine of that vintage?

 

[OBJ]

Re: Thermostat replacement on '79 Johnson

Naw....ya' ain't gotta pull the power head BWS. See that plate on the front of the head?....the one with about a bazillon 1/4" bolts holding it on to the head? Take those bolts out and remove the cover plate. The t-stat is at the top of the head.<br /><br />Check the Bomby site below. Lower left corner you will see "Engine Diagrams". Just click there and follow the instructions an you will see the parts break down for the engine.<br /><br /> http://www.evinrude.com/en-US/ <br /><br />PS...still working on getting the wiring diagram to Ya'. Simple scanner is on the fritz...

 

[blackwaterstout]

Re: Thermostat replacement on '79 Johnson

Okay. THanks Jim. Thats a little clearer. It's the plate near the spark plugs? To my suprise I stopped by my local Advanace Auto Parts today and asked if they had a sierra catalog. I looked through it and asked for a price on the Sierra thermostat kit. He looked it up and said he had it in stock! Totally caught me off guard. The kit was about $3 more than what I would've paid here at iboats, but I didn't have to pay shipping so it was actually cheaper. So I'll throw it on friday when I do the power pack.<br /><br />Question though. How durable is the water cover gasket? Reason is that Sierra doesn't make one of those and if I want one I'll have to mail order it. If I start to take it off and tear it or rip it I'm gonna be really ticked off at myself. It will cost me another week without the boat. I'm already running out of time. If the gasket has a tendency to tear, I may just replace the power pack and put the thermostat off until next week. Of course if I do that I want to keep a real good eye on that engine temp. What do you guys think?

 

[Solittle]

Re: Thermostat replacement on '79 Johnson

You wrote "I can't hold my hand on it for an extended period." That is both normal and desirable - 2-5 seconds is fine. Any longer and you engine is not getting up to the designed operating temp.

 

[blackwaterstout]

Re: Thermostat replacement on '79 Johnson

Okay thanks. Just seems like there a such a wide range of opinions on this issue. Many posts I've read seem to indicate that the head stays cool enough to touch it comfortably. In my case I can only touch it for maybe 1-2 seconds. The thermostat is a 143 degree thermostat. I know that when water reaches that temperature it will scald you. I misadjusted my hot water heater at home once. Mistakenly had it set for 140 degrees. The next day I was running some dish water and it was so hot it scalded me. I got a meat thermometer and held it under the faucet. Turned out to be about 143. I backed it down to about 125 which seams to be about perfect.<br /><br />Anyway, any thoughts on the water cover gasket. Does it have a tendancy to break? Or will I be able to reuse it?