Stuck Thermostat ???

[huckelberry]

I have a '78 25hp evinrude that I restored. Don't know the condition of the thermostst. I know it cools properly but I dont know if it closes to warm the engine in the winter months. Our water temps down here probably don't get below 50*F if that low. I have to use a barrell to run it so I can't do like the ear muff motors and wait for warm water to come out of the prop to test it. After removing the cover off my parts motor I'd rather not do it on my good one unless I know I have to.

I have known this motor all my life and it's seen it's share of salt water.

 

[agentjss]

Re: Stuck Thermostat ???

take the thermostat out and put it in a class of really hot water and see if it opens, then take it out of the water and see if it closes.

 

[huckelberry]

Re: Stuck Thermostat ???

I guess what I am trying to say is the thermostat is in the motor and I don't want to remove it to check it unless it is necessay for normal operation in cold water. It is open now but if it is stuck open, it probably is, will that give me a problem in +-50* water this winter.

 

[Vic.S]

Re: Stuck Thermostat ???

It is open now but if it is stuck open, it probably is, will that give me a problem in +-50* water this winter.

I think you misunderstand the way in which the thermostat operates. It should not be open now it should be closed. It should open when the engine temperature rises to its correct operating temperature. I dont know what that is, 60C 70C ( 140F 160F) ??, too hot to touch for more than a few seconds anyway.

You appear to be under the impression that it is open and only closes when the water temperature is fairly cold ie somewhat less than 50F (10C). That's not right.

Really the only way to test it reliably is to take it out and heat it slowly in a pan of water. It should start open when the water gets to the specified temperature (maybe marked on the thermostat) and close again when the temperature falls below that value.

You will get some idea by feeling the temperature of the head once the engine has been running for a while. It should be too hot to keep a finger on for more than a few seconds. If it is cooler than that then the thermostat is stuck open or opening too soon. If it is too hot to touch even briefly then the engine is overheating, possibly because the thermostat is not opening at the correct temperature or for other reasons.

I just looked at the diagram. I understand why you dont want to take it out Too many screws! (some are under a little cover with only three screws.)

If it was open when you put it in there then it's stuck open and needs changing!

 

[huckelberry]

Re: Stuck Thermostat ???

Vic s.

Your signature says it all

If it aint broke dont fix it.

Engine runs great, I'll leave it alone.

 

[twostroke87]

Re: Stuck Thermostat ???

You said the answer yourself

I have known this motor all my life and it's seen it's share of salt water.

If you have known the motor all your life, but do not know when if ever the thermostat has been changed, then it is time to change it. Driving around with a thermostat that is stuck open isn't really a big deal, you will just run a little cooler.

If one day though whatever is holding it open (probably salt crystals) breaks free, and the thermostat closes one day after you shut it off, and then doesn't re-open next time you use it, you will have an overheat problem.

Also if you drive around in cold water without the thermostat working properly, the engine won't reach operating temperature. You will suffer a loss in fuel economy because the combustion chamber is cold, and all of the fuel will not ignite properly.

It isn't hard to change your thermostat, go to your local johnson/evirude dealer (not autozone) and purchase the proper replacement thermostat and gasket.

The job may be tough, but you should do it.