Mystified!

Nodak7

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Sep 28, 2008
1,249
Hunter 41DS Punta Gorda, FL
Another mystery to solve! I have a Yanmar 4JH4E engine in our boat and the strangest thing has been happening (for quite some time). Whenever we motor for long distances I end up with some antifreeze under the engine. Always about the same amount (4oz). I have looked all around the engine and have found no indication of where it might be coming from. I changed the exchanger cap thinking it might be leaking by when the engine is running hard but it still does it. We make long runs up and down the ICW and this happens pretty consistently. At the end of the day the reservoir is empty and the antifreeze is under the engine. I put a mirror under the engine and see no telltales from where it might be coming from. Nothing in the back or the front either. I am mystified! Any suggestions?
 

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Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
Do you have an over pressure release hose or does the excess run back to a reservoir?
Does the cap have a pressure release that allows coolant to leak out to reduce pressure?
The association to long time running leads me to think that the leak is related to high temp pressure. You might use one of the white fuel pads under your engine to at least get an approximate area of the motor that is leaking. Like the cardboard pad under the car to see where the oil leak on the concrete is originating.
 

jviss

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Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
You can get some fluorescent leak detection dye, and a cheap UV light to find where it's coming from.
 
Jun 18, 2015
69
Mascot 28 Pilothouse Motorsailer Grand Manan
Service manual pg 279
Check overflow hose from pressure cap to overflow container.
 
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
Hot engines don't show little leaks for long. Use the cardboard trick of jssailem to isolate the part of the engine it is coming from. Work up from there. Look for "coffee stains" like you get on the counter when the water is gone and the coffee is left. Just a thin ring of residue.
 

Tim22

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Jun 16, 2014
254
Hunter 310 Ottawa
Check the reservoir. I had a similar problem and eventually tracked it down to the reservoir bottle. I never found the leak but found coolant dripping off the bottle. Replacing the bottle and hose fixed the problem.
 
Jun 11, 2011
1,243
Hunter 41 Lewes
On the back of the motor is a hose that comes from the engine block just below the elbow up to the heat exchanger. The side that was attached to the engine block had a bad hose clamp that looked ok but moved when you man handled it. I would check all the hose clamps on the back side of the engine. Good Luck.
 

gdudik

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Oct 25, 2017
87
Catalina 22 Vancouver, WA
If you are working with a standard radiator cap, you can rent them at most auto parts stores.
 
Jun 1, 2009
1,737
Hunter 49 toronto
Think I know the answer
For some reason, either Yanmar or Hunter put antifreeze drain hose with a small ball cock valve on it.
I had a HUGE disaster my first year with the boat, because the valve fell apart while the engine was running.
There was no indication anything was wrong, because the gauges didn't catch it.
Meanwhile, the alternator belt is flinging antifreeze everywhere, and the only reason I got away without a seized engine was you could smell something cooking.
Shut her down, and the whole engine pan, plus everywhere was covered in it.
So, I think you have a small leak in the intifreeze drain valve. Check it out
 

Nodak7

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Sep 28, 2008
1,249
Hunter 41DS Punta Gorda, FL
Lots of good ideas here and I will follow up on them. Last year I changed the cap thinking that might do it but that was not the case. I do like the idea of pressuring it up (with that tool) and checking around the engine. I will go to the auto store and see if they have one to rent or borrow. Since this happens when I am running I just have no way of seeing what is going on down there. As I mentioned I have looked the engine over a number of times after a run without finding a trace. Frustrating to say the least. Thanks again.
 
Dec 19, 2006
5,809
Hunter 36 Punta Gorda
On my boat my steps can be tilted forward and yes they come off that way but any way when motoring a lot
I will let my wife take the helm and go below and look around and see if any thing is leaking or not right.
I am also lucky and have a few doors to remove and well if I know some leaking like yours I move the tear mattress and get setup to try to find the problem.
Maybe one day just go motoring out in the harbor and put down paper toweling under the motor and give a look often
while motoring if you can but not sure if you can look down at motor while motoring around.
Nick
 

Nodak7

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Sep 28, 2008
1,249
Hunter 41DS Punta Gorda, FL
Well here is the result. I did rent a pressure device and tested the system. I found a cracked hose that had a small leak behind a fitting. It would leak while we were running and the heat from the engine would evaporate the antifreeze when the engine was stopped and not show a trail. Upon inspection the hose(s) were pretty badly cracked and could have failed so I am glad that I went looking for it. I also found a very slight leak at a fitting at the pump and will fix that as well. Lesson learned...check your hoses regularly. BTW I am finding it hard to find 5/8" hardwall water hose (green strip). Thanks again for your help with this. As usual you all are such a great resource for problems like this!