# Removing thermostat from Mercury outboard question



## FearNoFish (May 22, 2005)

I have had a lot of problems with the thermostat clogging up with what I believe is pieces of sargassum weed and causing the engine to overheat on my 2000 Mercury 125 hp ELPTO carbed outboard so I am taking it out for the summer. When you remove the thermostat do you still need to install the rubber thermostat gasket that goes around the edge of the T-stat? 


I would think not but the thermostat housing presses up against this rubber gasket that surrounds the T-Stat and forms what appears to be a sealed channel for the water to travel through and it would not be sealed without the gasket so I am questioning if needs to be there or not if the thermostat has been removed.


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## Sonnysmarine (Mar 18, 2007)

No does not have to be there, use sealer on the outside gasket, check the pressure relief valve for trash in also when you pull the cover off, it is right below the thermostat. I Do not recomend removing thermostats. Normally problem is still there, and the engine likes to be warm, and not cold, and will not idle well cold. Most motors now depeng on the thermostat readings to contol the ECU , yours is Carbed so will not affect it, but the thermostat also holds some water in so it does not dump the cold water before it removes the heat the engine builds up.


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## Bottomsup (Jul 12, 2006)

Sonnysmarine said:


> No does not have to be there, use sealer on the outside gasket, check the pressure relief valve for trash in also when you pull the cover off, it is right below the thermostat. I Do not recomend removing thermostats. Normally problem is still there, and the engine likes to be warm, and not cold, and will not idle well cold. Most motors now depeng on the thermostat readings to contol the ECU , yours is Carbed so will not affect it, but the thermostat also holds some water in so it does not dump the cold water before it removes the heat the engine builds up.


X2 Dont remove the thermostat.


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## ReelWork (May 21, 2004)

an engine that never warms to operating temperature can have bad things happen long term. Rings, cylinders and fuel/air mixture are all designed to work properly at a certain operating temperature. That's what the thermostat is designed for, to maintain operating temperature - not too hot and not too cold. 

Too cold and the engine may not get the proper fuel/air mixture - could burn more fuel and may load up excessively since the mixture may not vaporize the same at a lower temp. Also, you don't fire up a motor and then go run it hard do you - Why? Because you want it to warm up (which really translates into letting the cylinders/pistons and lubrication expand and work the way it was intended... This is the same thing, if the motor doesn't ever warm up then what's the difference since you're essentially running it cold. 

You get the idea... Keep those thermostats! 

I ran a 125 for 9 years and never a problem. Are you sure you're loading up with weeds or is there something else going on? (like a bad thermostat?)


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## PTH (Aug 22, 2006)

*overhating*

I used to have all the 90-125's get hot down here in the LLM. Mercury made a plastic screen the went into the gearcase in the water pickups. I kept those small pointy shells from getting into the system and plugging upthe holes that transfered water from the exhuast area to the area around the cylinders. Those gearcases have big pickups with no screens and they suck up all kinds of junk. I have to remove the water pump and base and drop in place.

Pete


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## Bottomsup (Jul 12, 2006)

The thermostat does far more than most people realize. You should not run your engine above idle before its starts peeing. Most scratches in the piston and cylinder wall happen when the engine is cold and the clearance fit is to tight. The cylinders and pistons need to be warm for proper clearance. Also no cylinder expands perfectly round when warm. Proper combustion is more of an issue on a carburated engine than an injected one. If the engine is cold and not burning all the fuel is can wash out the rings or worse carbon them until they are stuck. Excess carbon build up on the squish band and piston can lead to piston hitting the head. Excess carbon can cause pre-ignition problems also. Not having a thermostat can make an engine actually run hotter. The reason is that the water has to be in the water jacket long enough absorb the heat before it passes out. I had my eyes opened to this by a Lockheed aircraft engineer when I was manufacturing two cycle air cooled engines for Nasa and the US Navy. Same principal applies and everyone thinks the more airflow or water flow you have means better cooling but that is not the case.


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## mgeistman (Jun 13, 2012)

Just run a water temp gauge. Mine doesn't have a thermostat and it runs at operating temp. Just use common sence and Yull be fine.


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## ReelWork (May 21, 2004)

PTH said:


> I used to have all the 90-125's get hot down here in the LLM.....
> 
> Pete


Funny you say that - the LLM is where my 125 overheated (in face it was the only time it ever overheated)


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## FearNoFish (May 22, 2005)

This boat is a tunnel with a Nedski foil & jackplate and I do have a water pressure gauge- the needle will start fluctuating rapidly before it starts to over heat and adjusting the trime/jackplate makes no difference. Once I was racing in from offshore trying to beat an approaching storm and it overheated on me forcing me to to an on the water thermostat change and hitting the storm head on a few miles outside the Jettty. Last time it happened in the Jetties before I ever made it out, the only warning I have is seeing the needle on the water pressure gauge start vibrating.

What I am thinking of trying is just cutting out the T-Stat core from its frame; this will allow the T-Stat gasket to be used and will also restrict the ammount of water entering to that little hole on the cone end of the T-Stat that has a little cross-bar going accross it. I was going to cut off that little cross bar also so its just a small clean hole but I think I will keep it as it might prevent any larger junk sucked up by the intakes from reaching the water jackets. This way the T-stat area will be sealed since the gasket is still there and there will be also be some restriction in the chamber because it's not a wide open hole - all the water still has to flow through that small T-Stat hole, there is just no spring & plunger behind it to clog up.

Thoughts?


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