Weird coolant leak on Yanmar diesel

[GreenWave]

Looking for an engine guru who can comment on my obeservation.


I have a Yanmar 4jh3-TE diesel that has about 4700 hours on it. I have put the last 600 hours on this engine over the last 3.5 years. Yesterday while fitting a new alternator I found signs of an odd and concerning coolant leak. When I removed the alternator bracket mounting arm (on my engine this uses a threaded bolt just below the temperature sensor), some coolant dripped out of that bolt hole.


Some history... a few months ago I had a problem with the engine running hot and spent 3 weeks chasing it. I removed and cleaned the heat exchanger, drained and filled the coolant, and changed the thermostat. The engine then performed much better. 2 years ago, due to losing coolant, I changed the heat exchanger coolant cap (it was leaking). I have noticed that I still lose a bit of coolant when running the engine based on what is left in the overflow container.


So, do you think I have a major issue (cracked head). Any thoughts on how to proceed?

[Shrew]

If you're loosing coolant, such as the overflow container keeps ending up empty, yet there is no apparent coolant leak around the engine or bilge, then I would strongly suspect the heat exchanger.

Closed cooling side is typically higher pressure than the raw water side. pin holes in the heat exchanger tubing can transfer coolant to the raw water to be discharged out the exhaust.

I'd inspect, clean, test and determine if you need to replace the heat exchanger. With 4700 miles, I think it's getting close.

[GreenWave]

Thanks Shrew. After doing a search on Google I found another CF member who has exact same problem with coolant leaking out the Alt mounting bolt hole. Will follow his fix.
Having said that- I suspect I have other places like the HX where coolant may be leaking.

[deblen]

An automotive radiator pressure tester is invaluable for finding leaks.
Cheers/Len
https://www.amazon.com/coolant-press...ressure+tester

https://www.youtube.com/watch?v=L_Z1BeTMp5c

[bstreep]

A couple of other quick thoughts: The "radiator" cap has a gasket on it. They don't last forever. The water pump (coolant circulation, not seawater) has a limited life, just like on cars. They "weep" as they age, letting you know it's time to replace them. Just did mine on an older 4JH.

Leaks tend to "move" on engines (and boats in general).

[ScottRhodes13]

My 4JH2-HTE tends to lose coolant out of the reservoir. It just splashes out if it gets too high. Look for signs of that under the reservoir.

[GreenWave]

Originally Posted by ScottRhodes13

My 4JH2-HTE tends to lose coolant out of the reservoir. It just splashes out if it gets too high. Look for signs of that under the reservoir.

Does yours not have a lid? Anyway- no sign of that on mine. And my cap on the HX is sound. I suspect the water pump gasket is a culprit so will add that to future maintenance.

[ScottRhodes13]

Originally Posted by GreenWave

Does yours not have a lid? Anyway- no sign of that on mine. And my cap on the HX is sound. I suspect the water pump gasket is a culprit so will add that to future maintenance.

I do have a lid, and have tried to install a better gasket, but it still sloshes. I just keep the level on the low side and it works OK. I've seen it suggested that a head gasket leak can cause bubbling that can force the water out but I haven't checked for that. I hate to leave the helm when the engine's under enough load to cause it.