Thermostats in general

[Newyota]

I own two 80's Johnson motors and I can tell by the paint for sure that the one has never been removed the other I am not sure.After reading posts and info on the web what would be the easiest way to tell if it is not working short of just pulling it out?I read if you cannot hold your hand on it for about more than 10 seconds it is working anf they should open at about 160 degrees.Also, I was told it may not reach operating temps. on muffs, which is the easiest way for me to run it.If it is "NOT" working would my motor not run properly, such as a miss since it may not be at proper temp.I assume water temp. coming in can have a lot to do with it and ouside air temp in reaching the 160 degree mark.I am enjoying learning how to work on these, but really hope it is limited to minor/normal wear tear items.

 

[crazy charlie]

IF YOU ARE GOING THROUGH THE TROUBLE OF REMOVING THE TSTAT THEN YOU SHOULD 100% REPLACE IT AND THAT WILL BE YOUR ANSWER.FROM WHAT I REMEMBER ,THOSE ARE NOT EASY TO GET TO

 

[oldboat1]

Thermostats should be opening at 140F. 160 is overheating. Get an IR gun.

 

[Bosunsmate]

If its an early 80s and depending on model then you might need to move the tell tale outlet to the top of the crankcase, to not do this will result in air bubbles being caught at the top of the coolant chamber and overheat conditions to develop.
And yes they are a pain as you have to drop the lower cowling on many models

 

[boobie]

Got a model # ??

 

[Newyota]

It's an 1988 10RCCD,other is an 85' so they have the stat at he top and easy to get to.I would still like to know the symptoms of a bad one?If it stays closed what would happen?Open all the time what would happen?

 

[oldboat1]

If it's stuck closed, the motor will overheat (not enough cooling water flowing through head). If it's stuck open, the motor will run too cold. If in doubt, take out the unit and dip in a pan of hot water -- look for it to open. Will likely need a new gasket if you remove the thermostat.

If the t.stat is functioning right and the water pump/impeller is doing its job, the temp on the top of the head should hold somewhere around 120 to 140F or so (depends a little on the temp of the water in the barrel or the lake).

 

[Newyota]

Thanks..Now if it runs too cold will it idle rough or miss ..Just curious how it affects running.Have really not read anywhere about this,just what you explained,open too cold,closed too hot.

 

[racerone]

An evaporating liquid needs HEAT.---That is the basic principle of refridgeration.-----In an engine the fuel needs heat to vaporize properly.------There are other issues with expansion of materials as well.--So yes a cold engine will not idle properly !-----In aircraft a piston engine has a system to provide heat to the carburator to prevent icing !

 

[Newyota]

That's what I was getting at I guess and am aware since my old 1965 4stroke Honda MC runs differently in warm vs cold..So if I am trying to tune an engine on muffs with cool water and on a cold day like I was I may be beating my head against a rock due to the engine not coming up to proper temp. as someone had mentioned to me at one time regardless of a bad stat. which is a different problem than if you have warm water and a warm day.?I have this 1985 20hp that I converted to 25hp by changing the intake(same carb. is on the 20 and 25) that was making that inconsistent bad knock on a 35 degree day on the muffs that I think I posted about here or another site.Impeller failed while running so had to deal with that first.Think and hope it is just a "lean sneeze" and nothing more serious.Hope it is a matter of adjusting the slow speed screw.Could be an ignition problem or other? The service manuel calls for being on the water in gear from what I have seen on-line.