Yanmar4JH4E Exchanger Cap Leak

[Nodak7]

Interesting problem! The Exchanger cap for our Yanmar 4JH4E (54hp) leaks coolant even when the engine is cold. I purchased a new cap and replaced it but it still leaks. Actually seemed to leak worse. As long as there is coolant in the bottle it will allow it past the seal. The coolant in the exchanger maintains at normal level right at the neck unless running hard for a long time. I looked at the pressure spec on the cap and the old and new one is the same. I suspected that the seating surface on the exchanger might be dinged or warped but do not see anything there. I am wondering if I may have purchased a new cap that was not correct. Scratching my head over this one! Any suggestions on troubleshooting this?

 

[uncledom]

does it leak with the engine cold and not running?
does it leak as soon as you start the engine?

 

[Nodak7]

does it leak with the engine cold and not running?

Yup. Very slow but if I wrap a paper towel around the cap it will absorb it

 

[uncledom]

open the cap with the engine running and see if there is a pulse to it. one thing that comes to mind, and I'm sorry to even mention it, is a head gasket leak.

 

[Nodak7]

open the cap with the engine running and see if there is a pulse to it. one thing that comes to mind, and I'm sorry to even mention it, is a head gasket leak.

I had the same thought myself but determined that was not the case for a number of reasons. Let me know if I am missing something here. 1. I do not lose level in the exchanger itself when running or stopped. (always at the throat ). 2. It only appears to lose the amount of coolant I put into the bottle. 3. I am not seeing white smoke from the engine exhaust when I start the engine. 4. No oil scum on the coolant in the exchanger. 5. If the head were leaking would it not fill the bottle first rather than leak out the cap gasket?

 

[Sailgunner]

Call Neil

 

[Rick486]

Did you check that little hose from the bottle to the cap for a split, or leak? Is the hose tight on the nipple? Sounds to me like the small pressure difference between the bottle and the neck is resulting in a leak, which would also leak when the coolant expands under hard running. Gotta be something simple like the cap or the hose. How many hours on the 4JH4E?

 

[uncledom]

I had the same thought myself but determined that was not the case for a number of reasons. Let me know if I am missing something here. 1. I do not lose level in the exchanger itself when running or stopped. (always at the throat ). 2. It only appears to lose the amount of coolant I put into the bottle. 3. I am not seeing white smoke from the engine exhaust when I start the engine. 4. No oil scum on the coolant in the exchanger. 5. If the head were leaking would it not fill the bottle first rather than leak out the cap gasket?

Good points. Has anything changed, position of the over flow tank, anything? That cap has two seals, one is the inner and the other is the outer seal where it seems to actually be leaking. The cap allows fluid to move both in and out of the exchanger using the inner spring loaded seal but the outer seal has to hold at all times. Have you tried just getting a cap from the local auto parts store for a few bucks, given the same specs roughly, and throwing it on? A little scotch brite pad on the outer lip of the exchanger where the cap's out seal sits?

 

[seadaddler]

Is there anyone you know with same engine or similar to try their cap and as said check hoseand where hose goes onto?
Nick

 

[Marc14857]

If I understand correctly, I had a similar problem years ago. The tube or neck that exits the heat exchanger tank is rolled in place. (According to Mack boring) Mine developed a leak that I thought was the cap. I often found a small pool of antifreeze on the top of the heat exchanger though the engine never overheated. Replacement cap did not solve the problem. I ultimately applied high temp liquid gasket in a fillet type weld or small bead around the neck where it exits the tank which solved the problem. It has not reoccurred for many years. Hope this helps.

 

[mike311]

Nodak7,

Did you ever solve the problem with the leak around your radiator cap? I have the exact same problem with my Hunter 41 DS 2006 that I purchased last October. Please let me know what will fix it?

Michael