Yanmar 4LHA coolant overflowing

[timcub]

New to forum & first post so I hope this is the right place to post my question. Anyhow, recently purchased a 2004 46' Endeavour with twin Yanmar 4LHA-STP engines. Engines have about 2400 hours. First thing we did after we took delivery was have our local Yanmar service center inspect the engines and make any recommendations. He pulled all coolers, replaced any cracked hoses and flushed/cleaned both fresh & sea water coolers. Inspected all pumps & replaced any worn components. Upon reassembly, we took it for sea trial. Coolant levels were topped off to "full" on overflow tank and and exhaust manifold chamber topped off. It takes about 40 minutes to get to channel where we can open up throttles so we putter along at ~2200 RPM & during this time frame, everything looked good. Once we started cruising at about 3200 RPM, the coolant overflow tank began overfilling and after about 90 minutes it was spewing coolant out the vent hole on overflow tank. Also losing power.

Thought it was the exhaust manifold but upon further inspection, the turbo was cracked and had excessive radial clearance. That was replaced. Went on another sea trial and same thing happened except no noticeable loss of power, just coolant spewing out of vent hole on overflow tank. Again, this all occurred after about 90 minutes @ 3200 RPM.

So now we think it's the exhaust manifold and pull that and put in new one. Same thing happened. Coolant overflow tank level increases and then starts spewing coolant. All work being performed by Yanmar. Now he thinks the head is the issue.

This is only happening with STRBD engine. Anyone ever seen these symptoms before and if so, what thinks you?
Thanks in advance.

[ScottRhodes13]

Possibly a bad radiator cap, not holding pressure.

[timcub]

Possible but brand new OEM cap.

[a64pilot]

Very often it’s a blown head gasket.
There is a test sold at almost any auto parts store that will test for combustion gasses in the coolant, if you don’t have any, then it’s pretty unlikely that you have a blown head gasket, but if you have combustion gasses in the coolant, it’s pretty sure that you have.

Before you go tearing into things, purchase the test kit and test.

[timcub]

Originally Posted by a64pilot

Before you go tearing into things, purchase the test kit and test.

I see a few on the market, any particular one you'd recommend?

[skipperpete]

What engine temperatures are you seeing on the seatrials. Is the turbo jacket burning off paint?

[timcub]

Originally Posted by skipperpete

What engine temperatures are you seeing on the seatrials. Is the turbo jacket burning off paint?

No paint burning on turbo, looks like your typical Yanmar grey. Temps on both engines running steady at about 70-75 degrees C. No indication of over heating. Because we are only running high RPM for about 90 minutes, I don't think we are loosing much coolant. If I had to guess, maybe a quart at most. One observation once engine cools off, the level in coolant overflow tank never returns to "Full", but well above that mark.

[skipperpete]

Thats good news , sometimes they get an airlock and cause a false overheat accompanied by the ejection of coolant from the expansion tank. No overheating makes a diagnosis more difficult. If the test kit fails to provide an answer, perhaps consider a cylinder leakage test and a coolant pressure test. Hopefully the Yanmar techs will come up with a positive result before you need to do anything more.
Pete

[a64pilot]

Originally Posted by timcub

I see a few on the market, any particular one you'd recommend?

One of the ones with the liquid that changes color, I think some are electronic but you don’t need one of those

[SVHarmonie]

If you are actually adding liquid to the fresh water cooling circuit (and it sounds like you are) there is only ONE liquid that you can be adding: Salt Water.

Sounds like a heat exchanger leak to me.... USUALLY they leak the other way, but not always...

[CarlF]

Although it sounds counterintuitive, this could be caused by air bubbles in the cooling system. Did you bleed the cooling system after the heat exchanger work?

[timcub]

Originally Posted by CarlF

Although it sounds counterintuitive, this could be caused by air bubbles in the cooling system. Did you bleed the cooling system after the heat exchanger work?

Absolutely, had to top it off after running it dock side.

[Cadence]

Originally Posted by SVHarmonie

If you are actually adding liquid to the fresh water cooling circuit (and it sounds like you are) there is only ONE liquid that you can be adding: Salt Water.

Sounds like a heat exchanger leak to me.... USUALLY they leak the other way, but not always...

I would agree. Look at the heat exchanger. I've seen it cause that.

[timcub]

Originally Posted by Cadence

I would agree. Look at the heat exchanger. I've seen it cause that.

Yanmar tech said he's seen that at low RPM, but we are seeing the opposite.

[timcub]

Forgot to mention, overflow coolant tank had traces of carbon (black sooty like) in the bottom. Confirmed again this morning when cooling system was drained.