Small amount of oil residue in top of heat exchanger

Hi All, Recently purchased a 2001 Kadey-Krogen 48 North Sea with only 1,400 hours on the engine. The main power source is a John Deere 6068. This boat has mostly been used as a condo and we have seen a number of problems related to this. At survey the cooling system was pressure checked which required the removal of the pressure cap on top of the heat exchanger. All was normal and holding pressure. On the sea trial it was noted that at WOT the engine temp got to about 210 degrees F so was noted as slight overheating.

After 1,200 miles and a couple of hundred engine hours we asked a yard to look into the cooling problem. They sea trialed the boat and confirmed the temp rise that was seen at survey. When the same pressure cap was removed a frothy oil residue was observed on the cap and in the neck of the exchanger (see attached). There was no oily residue on top of the coolant and the coolant looked good in the overflow reservoir. A coolant sample was taken for analysis and no oil was noted in the sample. At this point I asked the yard to stop.

I am new to boat ownership but have fairly extensive mechanical experience and have some thoughts of my own as well as the speculation of the yard. Any thoughts or ideas as to the source of the oil in the coolant? Could it be a one time event based on a little used engine? Where should I start on my diagnosis? Thanks. Jim

That one is above my pay grade, but it makes little sense that no oil was detected in the coolant when you can clearly see it on the cap. Having experience pulling the head off my engine and afterwards finding the problem in the rocker arm (would not have needed to pull the head), there is certainly merit in taking whatever time is needed to properly diagnose.

Boatdiesel is a great site for these discussions. Some folks here comment there as well.

Jim:

Oil can get into the coolant system a number of ways: leaking coolant cooled oil cooler (if it has one), leaking head gasket/warped head, cracked block. Hopefully it is the easy one .

If the coolant system was pressure tested then the oil cooler leaking has been sort of ruled out, but not entirely.

The high coolant temps you are seeing is an indication that there could have been prior significant overheating event that could have blown the head gasket, warped the head or worse cracked the block.

There are specific diagnosis for each and I am sure that your mechanic knows them.

But if you don't have an oil cooler or it has been positively ruled out, you can just acid flush the raw water side of the main heat exchanger to improve cooling and keep an eye on it.

David

A small leak in your oil cooler could force oil into the coolant side. You could remove it and pressure test. And a good cleaning at the same time. Radiator shop could do it.
Broken impeller vanes or zincs can block water flow in the raw water side. Check from pump back to heat exchanger including hoses.

Maybe someone added water pump lubricant which is water soluble oil.

One aspect of this problem is that it appears to be transient. It is as if the oil path to the coolant was only open for a brief period. I too was surprised that no oil showed up in the coolant as I wouldn't expect all of the oil to precipitate out. It does appear that the amount of oil is small. I think that the first course of action is to re-pressure test the system. Then, oil cooler disassembly and evaluation. It is my expectation that it will pressurize and hold. I did replace the raw water impeller and heat exchanger zincs prior to our departure on the 1,200 mile trip up the coast. I will service all of the heat exchangers on the raw water side as a matter of baseline maintenance. At this point I think that operation of the engine is OK as long as we monitor it closely. Do you all think that is advisable?

Incompatible mixture of different coolants?

I had a frustrating experience with an old Continental Diesel, which had wet liners and similar specs to the John Deere.
This engine was WOT at about 1900 rpm, and would run all day at 1500. At 1700 it would run normally for about 2 hours, then the temperature would start to rise and it would start to spit coolant out of the overflow. It did not have a recovery bottle.
Coolant pressure tests showed zero leakage. Oil samples no antifreeze. The coolant was clear, when drained to change thermostat.
I finally had an old time mechanic look at it and he immediately diagnosed a head gasket leak based on a very slight brownish scum on the pressure cap and in the neck. It was not obviously oily, just scum.
We removed the head, and for sure there was a slight “track” on one liner top, and corresponding metal seal ring of the head gasket. The liner protrusion at that point was lower than elsewhere, and just at the minimum spec. A new head gasket fixed it.
My theory is that the peak combustion pressure is very high (over 60 bar at full load). The gasket held the pressure of the radiator tester easily, and the combustion pressure up to the 1700 rpm, but then started to leak combustion gas past the gasket in the one spot. This gas ended up in the coolant, with a minuscule amount of oily gunk. It caused an air bubble in the head, which caused the high temp indication, then escaped under the pressure cap leaving the scum. I ran for quite a while trying to trouble shoot, mainly running at lower rpm and successfully avoiding the issue.
For what it’s worth (analysis like this from far away by amateurs makes the worth de-minimus) I would pull the head. If liner protrusion is on spec, and head has no cracks and is flat within specs, put it back with a new gasket. If it is a leaky gasket you don’t want to run it until the head cracks or warps due to localized overheating.
In my saga I did also change the head, but that was only because I found a new-old-stock head at a price comparable to refurbishing the old one. I do not believe the old head was cracked, just the minuscule gasket leak at high load.
Good luck, and keep us posted!

Interesting thought the cooling system lubricant.

Jim,
If it was my "new to me" boat, I would ask questions of my mechanic using the info in Island Cessna's post (suggestions and experience), as the leaking head/liner (gasket) suggestion seems very plausible. Also, as you have a cooling issue and "gunk" in your coolant, I would give the entire cooling system a full maintenance to get to a new "starting" point maintenance wise. Flush coolant side and replace thermostat and rad cap, and new coolant (check to ensure compatibility with your engine some are coolant sensitive). Remove all raw water components (including exhaust elbow), rod and acid clean, new gaskets, and pressure test. Probably install new hoses and clamps while I was at it. Also, carefully check out the raw water pump, and install a new impeller if the pump is in good condition.
Other than the head suggestion, my ideas do not address the "oil" issue, but based on your coolant test results, your problem could well be what IC suggested??
Let's hope your issue is NOT caused by a cracked block!

Thanks for your comments Island Cessna. Your Continental Diesel experience sounds a bunch like what we are seeing. I was aware that we have wet liners and had thought about o-rings or a head gasket. We naturally want to avoid the head gasket if possible and try some of the easier, cheaper stuff first. It does make more sense than anything that I have considered. I will check the coolant sample for hydrocarbons although they may be transient in nature. Jim

Tom, Thanks for those thoughts. I will go through the entire system. It takes the JD coolant and that is currently installed. I did service the raw water pump with a new impeller and inspection and it was in near new condition. Not hoping for a bad head gasket but compared to a cracked block(!) that is what I will be prepared for. I am the mechanic but obviously will send the head out for testing and refurbishment if it comes to that. Not back to the boat till mid October so it all starts then. jim

On my Detroits, the raw water cools the coolant. The now cooled coolant cools the oil. Because the oil pressure is higher than the coolant pressure, any leak in the oil plates goes into the coolant.
Most of the time when I see a Detroit cap that looks like yours, it's a tiny leak in the oil plates.

Lepke, I can only hope for this so it is where I will go first. Thanks for the thoughts. Jim

I am wondering why 1200 miles (200 hrs) with a known overheating condition? I wouldn't go a mile further w/o getting to the bottom of the overheating and now possible head gasket problem. Have you priced a new engine?

Brooksie, I appreciate the thought but I am not too worried about the engine. All of the above is speculation. Overheating only at WOT and not that bad. I monitor the engine regularly and am prepared for problems. Could get worse and probably will but we all have different comfort levels and I am OK with the risk. It is something that needs to be understood and will be. I had no discomfort with the trip up the coast with the boat. There was no indication of the oil in the coolant when we left so the trip precipitated the problem. Could be a head gasket which is a fairly simple repair. I am going for basic maintenance first then to the oil cooler. I will test along the way but that will be by running the boat.

Are you POSITIVE it is oil?

Take a coolant sample and send it to a lab. $50 and fill in the form and you will get a reply within a week to any Email address you provide. As long as you can get Email you will get an answer.

Maybe it is just coolant degradation causing that muddy looking stuff. People wait far too long to do changes or just toss in any coolant without any effort at what the engine actually needs and/or mix different coolants. The result can be goo that looks like that.

If the antifreeze is too old it can also allow rusting which will change the colour to a muddy brown.

Find out what you have.

Caterpillar SOS test labs - used them for years.
Blackstone- no experience but good rep on the forums
There are others that are good too.

THey both test all kinds of stuff including coolants.

Have you dipped the muddy cap in a pan of clean water? If it is oil it will likely show a sheen.

Hey C lectric, thanks for the thoughts. Sent in a sample and received a "no oil found" result. Fluid is surely not rusty and is the bright yellow green of John Deere recommended fluid. Regardless, it could be something else which is interesting to explore. A previous comment suggested a water pump lubricant additive. Once I get back to the boat I will explore the sheen on water approach. Nice simple idea. Thanks.

Dip a strip of oil diaper into the coolant and see if it absorbs any oil. Also try a strip of paper towel. Water and oil will be absorbed up the paper towel at different rates and you might see a separation.

Lube oil and transmission coolers are the usual first suspects.

The coolant tests should also look for exhaust products.