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  #11  
Old 08-12-2013
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Re: Yanmar still overheating

One thing for sure My Yanmar 3YM30 does not have a separate pump for the coolant.
I did notice that even with a very good water flow at exhaust, the water was boiling hot, meaning that it would burn my hand .
Now that I am sure that the problem does not come from the seawater circuit I will drain and change the coolant and see if things improve.
Could it be that thermostat does not fully open , allowing engine to run under 2800 rpms without overheating , but not allowing enough flow of coolant after 3000?
Will remove thermostat and see if it works better without it

If nothing works this Yanmar will be a good mooring Well even not heavy enough
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Old 08-12-2013
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Re: Yanmar still overheating

You have to have a pump. Otherwise the coolant would not circulate. The pump is on the front of the engine(top center) and should be driven by the same belt that drives the alternator.

The best way to clean the heat exchanger is to remove the core and take it to a radiator shop. It should be about $30.
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Old 08-12-2013
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Re: Yanmar still overheating

Quote:
Originally Posted by THEFRENCHA View Post

Highest possible RPM is 3600 so fine according to the Yanmar specs , and then I should cruise at 3200

Here is my problem If cruising at 2600 absolutely no temp problem
At 2800 I get some grayish smoke but no overheat and all is well
At 3000 I get lots of grayish smoke, perfect water flow, BUT then afetr 10 minutes, engine overheat and alarm comes on.

When I shut engine down, engine cools in 20 minutes and if I restart and cruise at 2600 all is fine for hours.


Thanks
Did you check your boat's manual for a recommended max rpm? It might not be the same as the raw Yanmar specs. Does 2600 rpm push you along at max hull speed? The max rpm can vary depending on boat size, prop etc. I don't get anything near max rpm from my Westerbeke 55.
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Old 08-12-2013
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Re: Yanmar still overheating

Our 3HM putts along fine about 2000rpm. It will get hot if we run above 2500 rpm for long periods.

This might be a silly question... but have you checked your raw water filter and associated through hull recently? If our raw water exhaust output is diminished a clogged raw water through hull and/or raw water filter is usually to blame.

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Last edited by shanedennis; 08-12-2013 at 09:51 PM.
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Old 08-12-2013
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Re: Yanmar still overheating

Make sure your prop is clear. To do this, place the transmission in neutral and increase engine speed, slowly to 3200RPM. If it does not overheat, you need to pull the boat and check for barnacles, prop fouling, etc.

I have the same engine and used Prestone coolant (ethylene glycol based antifreeze), in a 50:50 mixture ( antifreeze : water ) this spring. No problems.

Also, do you have an engine heated water heater? If you do, do you get hot water? If so, your coolant system is probably ok.

Let me know how it turns out.

cb
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Old 08-13-2013
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Re: Yanmar still overheating

Quote:
Originally Posted by THEFRENCHA View Post
One thing for sure My Yanmar 3YM30 does not have a separate pump for the coolant.
I did notice that even with a very good water flow at exhaust, the water was boiling hot, meaning that it would burn my hand .
Now that I am sure that the problem does not come from the seawater circuit I will drain and change the coolant and see if things improve.
Could it be that thermostat does not fully open , allowing engine to run under 2800 rpms without overheating , but not allowing enough flow of coolant after 3000?
Will remove thermostat and see if it works better without it

If nothing works this Yanmar will be a good mooring Well even not heavy enough
It's a slippery slope to try and gauge water flow by eye or temperature by hand. Trust me, if you google 1GM10 overheating you'll find posts by me diagnosing basically the same issue you have - overheating at high RPM's. It was really really hard to tell (I had a raw water impeller blade jammed in my system for an entire year before it showed any issues).

I recommend getting an IR temperature gun to measure the engine temperature.


Also I don't know if someone else can comment but with my 1GM10 the exhaust water is always cool enough to touch. When it got hotter than that I knew the alarm was about to buzz. That said, with the heat exchanger your system is different.

If the exhaust water was getting too hot it would point directly at a flow problem on the raw water side.


Finally, I came across this:

Warning - Yanmar 3YM30

Quote:
"These early (2004/2005) engines have a 38-tube heat exchanger, and some very early engines were reportedly also fitted with a smaller capacity raw water pump than is now used. The fix is to replace the original 38-tube heat exchanger core with a new 63-tube one, and change the water pump if necessary.

If you have a Yanmar 3YM30 with an engine serial number under 6,000, I suggest you phone EP Barrus and ask if your engine is affected. I am not sure of the exact number of the last of the faulty batch, but Barrus know. Don't rely on your Yanmar dealer having just serviced the engine to know about this!"
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Last edited by asdf38; 08-13-2013 at 10:18 AM.
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Old 08-13-2013
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Re: Yanmar still overheating

Thanks everyone. This Saturday I am going to do the complete treatment
A) Flush with acid again It did improve the water flow circulation problem by cleaning the mixing elbow but maybe not enough at heat exchanger level
B) Drain and change coolant and use Prestone as recomended by Cjb
C) test the engine at sea , with and with the thermostat

I have the bigger water pump already ( and a strong output of water ) and probably the newer Heat exchanger This overheating problem is recent and started with a low water flow I thought it was fixed after the first acid flush as I have now the strongest water flow that I ever had

Hull and prop are clean so at least I think that The problem is within the engine itself
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Old 08-13-2013
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Re: Yanmar still overheating

maybe it is not the engine but the temperature switch. mine went off one day half way home and the engine was not hot ( I could put my hand on the head and block and it was just warm). we disconnected the switch and tested when we got to the dock and found that it would trigger at 100 degrees and should have been at 140 degrees, replacement was $19
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Old 08-13-2013
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Re: Yanmar still overheating

Frencha - check out this site - it is for the saildrive output, but it a great resource for you to help you get around. The heat exchanger is the bundle of brass tubes.

Yanmar 3YM30

See also -
http://www.yanmarmarine.co.uk/pdfs/s...al/EPB5552.pdf

I don't know if you have the manuals or not.

Have fun this weekend.
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Old 08-14-2013
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Re: Yanmar still overheating

I believe some one mentioned checking the thermostat. There is a test where the thermostat is placed in a cup of water and then slowly bring the water up to temp. where the bimetal will open the thermostat. Replace if the thermostat fails to open with in the prescribed spec. in your Yanmar service manual(everyone should have one onboard).

Last edited by aa3jy; 08-14-2013 at 07:06 AM.
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