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Discussion Starter · #1 ·
I have heard people say that they remove the thermostat on their 25 horse Merc 2-smokes and it works fine and can never stick closed and fry the engine.
Urban legend or truth?
Mine seems to run hot and the pisser water is actually steamy and hot to touch but it seems to cut off and on properly and has been working great.
 

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Here in Florida a lot of people just toss 'em. It only functions to help the engine warm up in extremely cold (at least to us Floridians) environments.

You won't hurt anything leaving it out, but watch out when taking out the thermostat bolts. They tend to be really well... They suck. They're really skinny and long and made out of less than average quality stainless. One was broken on my 25 merc and I had to go through the whole ordeal of taking off the water jacket, breaking like 5 more bolts there, and finally having to get a bunch of helicoils and some welding done.

I'm not saying don't give it a shot, but if they don't come out with ease, I would just say "If it ain't broke, don't fix it" ;)
 

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I strongly disagree. The purpose of the thermostat is to keep the engine at proper operating temperature. It allows parts like the pistons to expand and give a better seal, and provides the Ideal temp for combustion. Long term you will surely shorten the life of the engine. A thermostat does not open up and stay that way but opens and closes as the temperature in the engine changes. That way it maintains the temp at which it was designed.

Bob
 

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From what you describe your wizzer is doing you have a problem. It should be a steady warm stream like when I was 20. The wizzer water does not go through the thermostat.

Have you replaced your water pump impeller lately?
 

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From what you describe your wizzer is doing you have a problem. It should be a steady warm stream like when I was 20. The wizzer water does not go through the thermostat.

Have you replaced your water pump impeller lately?
On the 25 Merc's, the water passes through the thermostat just before exiting the motor. In essence, it controls the strength of your stream. Having owned one, I can tell you that it is normal for the stream to be pretty hot. Unless you're loosing pressure at high RPM or your wizzer stream turns to steam, I wouldn't worry about it.

Of course, you should routinely maintain these parts. The Merc 25 is a simple motor and will last you many hours :)
 

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Discussion Starter · #6 ·
I have always been amazed how hot the water is. In all times except the heat of summer you can actually see steam coming off the stream from the heat and it's too hot to put your hand under it more than a few seconds. But it has behaved the same for at least 70 hours now since I bought it used with no problems even after running around at 6000 rpm most of the time so it seems to be fine. Being 5 years old I want to put a new impeller and probably water pump in to be safe. You can tell the t-stat is working since it cuts on and off when warming up in the morning after starting.
 

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Sorry, for some reason I had 9.9 on the brain. Mine wizzes all the time. Now I have to look to see if that is normal ;D
 

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I would assume that the themostat is similar to a car...180-190 degrees. Yup, can't hold your hand under that. Sounds normal, just make sure you have a steady stream and you'll be fine.
 

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I would assume that the themostat is similar to a car...180-190 degrees.  Yup, can't hold your hand under that.  Sounds normal, just make sure you have a steady stream and you'll be fine.
It's 120 degrees on the 25 Merc 2 smokes
 

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unless your fishing in canada i'd pull the thermostat out and not give it a second thought.... that is if you can do it without breaking the bolts otherwise leave it
 

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Here's what another Forum has to say about it.


http://forums.iboats.com/showthread.php?t=249973
they're talking about thermostats in general, we're talking about the merc 25 hp 2 smoke..... i do belive though that a thermostat is a critical component in some engines
 

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I would think if the motor was warmed up slowly it might be OK but most of you guys fire up ant then go Wot within seconds ...

Dave

*** But I am going to Make sure I have one in my merc ... Less wear Higher resale ;-)***
 

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Merc must have a reason for the motor to operate at 120. Water temp around here is 70 to low 80's, :(
 

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umm ******** take thermostats out. if you take the thermostat out it doesnt build any pressure that it needs. also if water is freely flowing it actually goes thru the cooling passages so fast theat it doesnt absorb the heat which in tern actually makes it overheat.. its like if you are in the hot sun sweating and you run thru your house and back outside. did you actually get any cooler? i think not.. but im only a yamaha master tech so what would i know.. :eek:
 
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