Yanmar Thermostat

Greever

Super Anarchist
4,091
106
Rockford, MI
So I have a Yanmar 2QM-15 on SevenSundays. Raw water cooled.

Since I launched her last week, I can't run her for more than 10-15 minutes before the cooling water buzzer goes off.

She has a new impellor, new mixing elbow, clear strainer and seacock, and has a shitload of water exiting from the stern. The only other thing I can thing of is the thermostat? Are the thermostats on these engines like a car? In other words, can I remove the thermostat and see if she still overheats? I suppose if I remove it I can also get a look at parts of the cooling jackets?

Any help would be greatly appreciated!

Signed: "Overheating on Lake Muskegon" :(

 

Dan33

Super Anarchist
Dear Overheating

The manual for the Yanmar 3GMD on GK states clearly...DO NOT RUN ENGINE WITHOUT THERMOSTAT.

I have found Yanmar thermostats to be unreliable. They seem to fail half open. That maybe enough to restrict your water flow through the engine and simply short cut it to the exhaust.

 

Dan33

Super Anarchist
Greeve...you can always remove it and test it in boiling water....start in cold water and put in on the heat and see if it opens at the proper temp. Make sure it opens fully.

I would change it no matter, but that might answer your questions, or provide you with a tested spare if it's not the stat.

 

Crash

Super Anarchist
5,093
1,019
SoCal
I will be getting a new one from Torresens this week. We will see how it goes...

Greevs,

Did you stick you hand into the exhaust? Did it feel hot or just warm? If the exhaust water isn't hot, then the possibility exists that you have a bad sender unit...or as I recall the engine control panel has a toggle switch to test the alarm. If the toggle spring weakens, the toggle switch can trigger the alarm to sound (in the test mode) even if all is running fine...

Crash

 

Dan33

Super Anarchist
Greevs,

Did you stick you hand into the exhaust? Did it feel hot or just warm? If the exhaust water isn't hot, then the possibility exists that you have a bad sender unit...


If the stat is not working I think the water can enter the engine and bypass the the cooling jacket. This is why a stat is used, to trap hot water as required, and keep the engine at a proper operating temp.

If I'm right the exhaust water could be cool, but the water retained in the engine could be VERY hot.

I think.

 

Crash

Super Anarchist
5,093
1,019
SoCal
Greevs,

Did you stick you hand into the exhaust? Did it feel hot or just warm? If the exhaust water isn't hot, then the possibility exists that you have a bad sender unit...


If the stat is not working I think the water can enter the engine and bypass the the cooling jacket. This is why a stat is used, to trap hot water as required, and keep the engine at a proper operating temp.

If I'm right the exhaust water could be cool, but the water retained in the engine could be VERY hot.

I think.
Gate,

You might very well be right...

Crash

 
Do you check the antifreeze/coolant level? Bleed all the air out of the engine coolant system? Sometimes trapped air will collect in the thermostat housing, the coolant circulates, but the temp sender is uncovered thus is sensing the temp of the metal around it not the cooler coolant. If you have an waterheater heated by engine coolant, make sure the lines to it are full as well.

 

Recidivist

Super Anarchist
GK, I have a 3QM30H that was exhibiting the same symptoms you describe, and I also suspected the thermostat.

I say "was" because the symptoms changed - a cable tie broke, a hose shifted and leant against a belt - a hole ensued and water sprayed around a bit. By the time I replaced the hose, I now had bugger all water coming out the exhaust and the motor really was getting hot. I suspect I have an air leak somewhere and haven't got it sorted yet, so I can't confirm your thermostat theory.

Only last year I flushed the motor with a liquid that the Navy uses to clear cooling galleries. My marine engineer reckons this stuff is amazing (at $90 a litre, it needs to be good!). Anyway, I ran the motor so it got hot, and recirculated the magic stuff to the extent it was giving off a bit of steam in the bucket, so certainly the thermostat should have opened and been cleaned, but it could have failed since then I suppose.

I would be very interested to hear what you find - it's my next job after I finish a major chainplate rework.

Cheers

R

 
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ozzy58

Super Anarchist
1,592
1
have the problems started because the sacrificial zinc anode needs changing ?

............. raw water cooling MUST HAVE

 

floating dutchman

Super Anarchist
Don't run the engine without the T-stat, It WILL just overheat, I'm 99.9% sure of this.

If the temperature sender was faulty I doubt you could run it for any length of time before the thing started beeping at you.

My T-stat failed on me but mine failed closed (or open, depending how you look at it), The engine was just on full cooling all the time and never came up to temp. I suspect that they are designed to do this so if they fail you can still get home.

Failed to not cool seems odd. One year after replacing mine (in salt water) I found mine partially seized, A bit of fucking around and freshwater and moving it back and forth freed it up, Even put some Lanocote (yea lets hear the Kiwi Ky jokes) in the interior to make me fell better, doubt it actually did anything.

Take it out, Its only two screws (from memory) and two hoses, study the way the water flows and you'll work out what part is supposed to move. Then put it into the "If it doesn't work force it. If it breaks, It need replaced anyway" category and have a go at it, It might just need freeing up.

 

ozzy58

Super Anarchist
1,592
1
no zinc = thermostat will deteriorate due to electrolysis / galvanic action if in seawater ( dissimilar metals )

as will other parts on cooling intake / outlet system .... wherever dissimilar metals are

 
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Gate,

You are correct, I missed "raw water" when I made my reply. I think your analysis in #7 is correct. Water will bypass until the themostat opens to allow cold water into the block for cooling. If the thermostat doesn't open, plenty of water pumps but it all bypasses the cooling jackets on the engine. The reason for not running the engine without the thermostat is that the engine will never come up to temperature with a constant flow of cooling water running through it.

 

Crash

Super Anarchist
5,093
1,019
SoCal
And because by the time you've opened it up to remove the old thermostat...and changed the housing gasket so it doesn't leak, you might as well just put a new thermostat in:rolleyes:

 

Greever

Super Anarchist
4,091
106
Rockford, MI
And because by the time you've opened it up to remove the old thermostat...and changed the housing gasket so it doesn't leak, you might as well just put a new thermostat in:rolleyes:

Yah, got a new one yesterday. Some zincs too...

Thanks for all the advice fellas. I will let you know how it goes this weekend...

 

Dan33

Super Anarchist
Greeves

The Yanmar cooling system is simple...you'll solve it.

I spent hours trying to solve a problem with the bow light on GK. Test light, multimeters. It couldn't be the bulb, it was replaced last Fall and only had been used for 15 minutes. It was the bulb.

Sometimes a duck, is just a duck.

 
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