losing coolant from Yanmar 4JH-H2E

[sailingduke50]

Over the past couple of years, I have been losing coolant from my Yanmar when I run it (going along the AICW) for 8 to 10 hours per day (at ~2300 rpm). I lose about 1 to 1.5 cups per day and replace it at the start of each day. I had the hoses changed or had double hose clamps installed. Coolant is not leaking into the bilge, underneath the engine and is not leaking on the engine; there is no increase in the overflow tank. Has anyone experienced this on your boats?

[Tim R.]

Yup. Actually fairly common. I found a few other occurances of this exact problem when I was researching mine. My 4JH-2E(1997) started leaking a very little bit like this a couple years ago. The combo exhaust manifod/heat exchanger housing corroded a pinhole from the fresh water(coolant) side to the exhaust outlet side. I could barely detect the smell of AF in my exhaust. The leak got worse and I had to replace the manifold($1,000). Here is a photo of the leak. The new part has a substantially thicker cross section so Yanmar knew about this vulnerability and modified the design.

[Rubikoop]

It could be seeping into the raw water side of your heat exchanger or a tiny leak from a failing head gasket. You're sure there's not a tiny drip from your water pump?

[Tim R.]

Originally Posted by Rubikoop

It could be seeping into the raw water side of your heat exchanger or a tiny leak from a failing head gasket. Your sure there's not a tiny drip from your water pump?

Good point here. Check the O-rings on your HE caps. Could also be a leaky HE core.

[sailingduke50]

Thank you Tim R. and Rubikoop for sharing your photo and information.
I did not see any leaks at the water pump">raw water pump while running the motor but I will check the HE and gaskets. Must go to another pile of $$.
Have a great one.

[Rubikoop]

Originally Posted by sailingduke50

Thank you Tim R. and Rubikoop for sharing your photo and information. I did not see any leaks at the raw water pump while running the motor but I will check the HE and gaskets. Must go to another pile of $$. Have a great one.

You want to look around the coolant pump not the raw water pump.

[Tim R.]

Originally Posted by Rubikoop

You want to look around the coolant pump not the raw water pump.

Specifically, there is a weep hole right under the shaft housing behind the pulley. Get a paper towel and with the engine off, wipe it around that shaft housing and see if there is any evidence of coolant. It would also drip down the front of the engine from under the pulley and end up in your engine bilge. I know you stated there is none there but a little bit mixed with water would not show up as pink. Could also be evaporating before getting to the bilge but you would smell that. Sort of like a maple syrup smell.