Coolant leak on a 41DS

[chinagirl]

Hi all.  I have a 41DS with a Yanmar 3JH5E diesel.  I have a very slow (about 5ml per month) coolant leak into the sump space below the engine.  Does anyone have any suggestions where this might be coming from? Thank you.

[Mistroma]

I had a similar leak with my 4JH4AE and tracked it down to the alternator pivot arm. Yanmar put the bolt through a waterway and it is a really bad design. It leaks whenever you adjust the belt tension but is never obvious. I put some tissue under the point where the arm meets the engine and it soaked up the leak.

My solution was to remover the arm and bolt, push a rubber grommet over the bolt and squeeze it into the hole. It isn't perfect but usually seals completely when everything has been tightened. I sometimes paint some varnish around that area.

It usually doesn't leak again until the belt tension is adjusted.

I've no idea if the 3JH5E has a similar issue but it is worth checking around where the altenator tensioning arm meets the engine casting. The 3JH4E looks similar to my 4JH4AE.

[bereboot]

I also had a very smaller leak
Finally i found that it was the rubber joint of filling cap on the engine that was leaking.

[mic98034]

I had a similar leak in 2022. I have a 2011 39i with a 3JH5E. The leak was coming from the rear cover on the heat exchanger. Since it was a slow leak I didn't get to it for a year. I bought new a seal thinking that would fix it. But when I removed the cover I discovered that the aluminum of the heat exchanger at the point of the leak had corroded enough that it would never seal, even with new seals. I theorize that the corrosion happened because 1) the previous owner had filled it with the old style "green" coolant, 2) I didn't fix it when I first noticed the leak and therefore coolant in the area of the seal corroded the seat of the seal to a point that it was not repairable. I had to install a new heat exchanger. $3000+   ouch!!!

You've been warned.