Overheated my Yanmar 20gm20f - SailNet Community

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Old 07-13-2012
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Overheated my Yanmar 20gm20f

Ahh the wonders of a new used boat.

Seems I found out the hard way that I have a coolant leak. Here is what happened:

The alarm went off but no light went on (figured out the bulb is out) close to a breakwater so I had to run it for a couple of minutes to clear. Started it again twice for just a minute to get into the wind to get a sail up...

Let it cool, cleaned the strainer and it had a bit of grass in it so I thought that was a fix. Started it up, she ran for 10 minutes and the alarm went off again. Shut it down right away sailed to the mooring. Figured out that there was almost no antifreeze in the freshwater side (the leak is an easy fix)

THE BIG QUESTION: Did I do any damage? Is there anything I should/could do?
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Old 07-13-2012
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Re: Overheated my Yanmar 20gm20f

Really depends how hot it got. If you stayed under 220, you're probably ok, but above that you start warping heads, etc.

Usually when an engine overheats you change the thermostat just to be on the safe side.
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Old 07-13-2012
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Re: Overheated my Yanmar 20gm20f

Sounds like you are fine. Will take more than a couple of minutes running hot to do any damage. Do keep an eye on the oil to see if it gets milky indicating water getting in like from a head gasket and/or warped head just to be sure.
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Old 07-13-2012
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Re: Overheated my Yanmar 20gm20f

Thanks, I feel a little better..
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Old 07-14-2012
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Re: Overheated my Yanmar 20gm20f

it takes more than one would think,the main thing is let the engine cool down before running cold water thru it,i've been known to forget to turn on the water inlet,so far i've been lucky,jims right just keep a watch on your oil for milky appearance for a while
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Old 07-15-2012
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Re: Overheated my Yanmar 20gm20f

Just a thought: any chance the water pump impeller got overheated or damaged from dry running and bits of it might get into the cooling passages? And, if so, will they flush out with normal water circulation?, or will a manual flush be needed?
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Re: Overheated my Yanmar 20gm20f

Quote:
Originally Posted by Skipaway View Post
Just a thought: any chance the water pump impeller got overheated or damaged from dry running and bits of it might get into the cooling passages? And, if so, will they flush out with normal water circulation?, or will a manual flush be needed?
thats a good point,it only take a few seconds to wipe out an impeller,you should be able to determine how much of the impeller is missing
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Re: Overheated my Yanmar 20gm20f

Just discovered this thread which may be of interest:
destroyed impeller
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Old 07-15-2012
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Re: Overheated my Yanmar 20gm20f

One of the things I checked before checking the freshwater side coolant level was the raw water impeller and it's fine.

The impeller on the freshwater side has not been checked yet but it seems that this is more along the lines of an automotive pump and running it dry for a short period would not effect the impeller.

I think I found the coolant leak. The lower "drain valve" with the clear plastic tube attached has a round nob for opening/closing. I noticed coolant coming out when I refilled with antifreeze. I tried tightening it and it seems that the nob will turn all the way past where it starts to feel like it's closing, leading me to believe the valve was over-tightened in the past and is now stripped or broken internally. I have yet to remove it as I could fiddle with the valve and get the antifreeze to stop leaking and only drip when running.

I'll probably have to order the part, so, my next question is, can I simply plug the hole with a properly sized bolt and run the engine until the part comes in?
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Re: Overheated my Yanmar 20gm20f

Seems to me that would work with a small hose clamp on it. Yanmar, I believe, recommends that the valves be adjusted after an overheat. Like others have said check the oil which, you might want to change for the heck of it and look to see if you're putting out a lot of smoke when you start her up. If not you're probably fine.

I overheated my 3gm a few years back and it was obvious that I had damaged it (burned up a piston ring). I had excessive smoke when I started the engine until it warmed up. My mechanic said run her till it dies. I lasted one year before I got tired/embarrassed about the smoke on startup.
Good luck
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