Small Coolant Leak

[Marc14857]

I have a very small coolant leak on the Yanmar 4JH4E ever since I took possesion of the boat. After running the engine for awhile, I often find just a few drops of coolant on top of the coolant resevoir in the area of the radiator cap. I usually notice the coolant after the engine has cooled down and I happen to be checking the engine prior to departing on the next trip. I have replaced the radiator cap with a new one but that has not helped. I also put a hose clamp on the overflow hose where it connects near the radiator cap and this has not helped either. I am wondering if the neck (pipe) that the radiator cap attaches to is perhaps rolled into the radiator resevoir cover and perhaps this rolled joint is leaking. If it is leaking its got to be a very small leak as the engine runs fine and does not overheat.
Anyone have a similar issue or suggestion?

Thanks
Marc

 

[Vinny]

Are you sure you replaced it with the correct cap pressure?

Maybe the one that was on there was the incorrect pressure.

I don't remember the correct pressure but 7# should do it.

Rick do you know off hand?

 

[Alan]

Borrow or buy an automotive coolant pressure tester. It is a simple pump with a pressure gauge attached. Pump up the pressure not to exceed 15psi and wait. If you do have a leak the gauge pressure will slowly drop and the leak should present itself.

 

[Rick Sylvester]

I don't, Vinny

but you're probably in the ballpark.

Alan's suggestion is excellent since at this point you'd want to recreate the leak. I was going to suggest bringing the engine through a complete heat cycle under observation which is a similar, but less controlled, version of what Alan said.

In any case, he'll want to find the problem because a) it probably won't go away, and b) it'll probably get worse.

 

[Vinny]

but you're probably in the ballpark.

Alan's suggestion is excellent since at this point you'd want to recreate the leak. I was going to suggest bringing the engine through a complete heat cycle under observation which is a similar, but less controlled, version of what Alan said.

In any case, he'll want to find the problem because a) it probably won't go away, and b) it'll probably get worse.

Agreed.

 

[Marc14857]

Pressure Test Was OK

I borrowed a pressure test kit from Auto Zone (no charge) and performed a pressure test at 14 PSI for about 5 minutes. The pressure held fine. Also tested the radiator cap which tested fine. Starting to wonder if the leak is from where the overflow hose attaches to the expansion tank. I know this section of the system does not see any significant pressure but maybe when the coolant expands into the tank it is leaking around the nipple. I'll have to check the hose a nipple a little clloser next week

 

[Vinny]

I borrowed a pressure test kit from Auto Zone (no charge) and performed a pressure test at 14 PSI for about 5 minutes. The pressure held fine. Also tested the radiator cap which tested fine. Starting to wonder if the leak is from where the overflow hose attaches to the expansion tank. I know this section of the system does not see any significant pressure but maybe when the coolant expands into the tank it is leaking around the nipple. I'll have to check the hose a nipple a little clloser next week

The pressure tester doesn't lie. Look for the impossible. The bottom of the bottle, at the seam or on the side at the seam, the hose connection at the neck nipples both at the bottle and where the exit at the cap is. The hose itself.

You are almost there.:dance:

 

[Alan]

Vinny, the overflow nipple, hose and expansion bucket are not part of the pressurized cooling system. The pressure tester does not test for leaks there. A good visual will be able to check that. If in doubt just replace the overflow hose.

 

[Vinny]

Vinny, the overflow nipple, hose and expansion bucket are not part of the pressurized cooling system. The pressure tester does not test for leaks there. A good visual will be able to check that. If in doubt just replace the overflow hose.

Alan,

I'm aware of the fact that the pressure tester doesn't test the overflow system. That was my point. The drops are coming from outside of the pressured system. There are only a few places to look. The bottle needs to be checked very carefully. Not under pressure but when it is hot from the fluid that has expanded into it. The hose or the clamps could be the problem but the leak may just be heat related. Other wise the bottle or hose would, over time leak all of the fluid out, even when it is cold.