coolant in oil sample

[ezbry]

We purchased a 79 42'LRC last april. Love it. Still learning after a year. Tested engine oil at the time of purchase even though uncertain about hours on oil. Sample was normal. Recently tested again after 100 plus hours. It shows trace of coolant. Any suggestions where I start before bringing a marine mechanic on board. 4-53 Detroits. Showing also abnormal but not critical iron levels. Have changed oil but need some guidance. Really enjoy this forum.

[Genesis]

... are not unusual if the boat is not run a lot. You get a lot of start-up wear on cylinders when you only run every couple of weeks. Ignoring that one is probably ok.

HOWEVER, coolant in the oil is VERY BAD. Even small amounts of coolant can cause spun main bearings. The most likely cause is a bad head gasket or cracked head, although there are other possible sources as well.

Get to the bottom of this before you get an ugly and expensive surprise.

[ezbry]

Thanks Genesis,
I do realize the seriousness of this and my first guess would also be the head. I am just glad that I did take oil samples and am catching this before it was too late.

[Nonchalant1]

4-53's are wet liners (cylinder sleeves surrounded by coolant, not a solid engine block). I'd start from the easiest possibility then progress to the hardest.

Whe you look at the pulled oil and oil on the dipstick, does it have any flecks of grey? Or just all black? If all black, sometimes a second opinion is worth the trouble. I've seen the same oil come back differently from different labs. If the second sample also shows a "trace", get on it right away. Karl, if he gets a second sample from the same oil, and it doesn't show coolant, should he maybe run it for 5 hours or so and test it again?

Next easiest thing to check is for bad cylinder head torque. There's a warm engine torque and a cold engine torque. Get a good torque wrench and check either on every head bolt. Depending on your mechanical skills, you might do this one yourself.

Is your oil cooler also cooled by coolant instead of raw water? (mine is). If there are gaskets to check and bolts to check torque, that may be an item to check yourself too.

If the head torque and oil cooler are OK and you don't want to do the next bigger, head gasket job, I'd call in a Detroit Diesel service center mechanic. They really know their stuff up here. About $100/hr plus travel, but they may do it faster and better. They're on the web and there's a service center lookup.

Doug Shuman

[Genesis]

You have to define "trace" - glycol is usually expressed as either present, not, or "oh $hit you're screwed".

The latter doesn't require an oil analysis to see.

The oil cooler core CAN be the cause of this, but its not terribly likely if this is an isolated issue with nothing else going on.

I'd pull the oil cooler before I pulled the head, to be honest. Its easier and YOU can do it. However, make damn sure you can get all the gaskets first, because without them its not going back together. You will also need someone's help to test it - the proper procedure requires making up a blanking plate so you can put the oil side under shop air pressure (~50-60lbs or so) and then immersing it in water to see if you get bubbles. There is a risk of rupture when you do this, so care is required.

BUT - in nearly ALL cases if you have a bad oil cooler core you also have oil in the coolant. Open up the neck in your tank and look. Oil floats, so it'll be VERY visible. The reason is that oil pressure is vastly higher than coolant pressure - so the leak is in that direction. When you shut down coolant will get in the oil, but its basically impossible to get that without major cooling system contamination.

Hope you DO find that, by the way, although it too is a royal pain - you need to flush the cooling system and run a de-oiling compound in there if it has gotten oil-contaminated - this is very, very important because oil in the cooling system will impede heat transfer enough to cause major trouble in the form of hotspots in the engine.

Wet liner engines are subject to severe damage if overheated - even slightly. The seals are just O-rings and if you "cook" them, even a bit, they will leak. That's a very, very common problem - the second being the head (cracked) or head gasket. The root cause of BOTH maladies is usually an overheat. My general "rule of thumb" is that if a wet liner engine is overheated and the head comes off (e.g. cracked, blown head gasket, etc) I give serious consideration to a full major, because it sucks to have to tear into it twice and there is no way to know for certain that the liner seals are ok after such an event.

Retorquing the head will usually not fix this kind of thing. Among other things unless it was done wrong originally or a bolt has failed due to a manufacturing defect the odds of trouble here are slim and none. Once the gasket fails it has to come off and be replaced most of the time anyway. Internal coolant leaks are extremely damaging - into the oil is bad, and into a cylinder is frequently worse, since its entirely possible to hydrolock a hole and if you do then you will snap the conrod when you go to crank up. That sort of failure can hose the block and leave you with a non-rebuildable engine.

[jim rosenthal]

...had this a year or two ago, it turned out to be one of the French made CAT blocks that had casting defects in them and there was a passage someplace from the oil path to the coolant path. Sort of an internal fistula, if you will. They rebuilt the engine around a new CAT block, but the point is they could never find the fault in the old block. You may unfortunately turn out to have the same thing- having to major the engine but not knowing where the actual leak is. What about an exchange long block?

[Genesis]

... especially those french block CATs (mostly 3116s)

That left a VERY sour taste in my mouth regarding Cats. Indeed, I'm not sure I'd buy a boat with them in there after the way this was handled. They DID NOT step up and swap all the potentially bad ones - rather, they waited for failures, and for some people who don't run the boat much, its entirely possible that the warranty could expire first!

[ezbry]

The dipstick did not show any trace of flecks of grey. It was just typical black. Unfortunately I did not save any oil for a second sample but have learned my lesson on that one. Next time I will have that spare sample waiting for retest.

The "trace" of coolant is the lab terminology and I take it to mean present in small amounts.

I see no sign of oil in the coolant so would think that might rule out the oil cooler leak.

The engines have never run hot while we have been the owners.

I am going to re-torque the head and monitor coolant level on the slight chance that it would cure the problem. If there is a change in coolant level then rebuild would be my option. Do you think I am sticking my neck out on trying this first? I would think the biggest percentage of coolant would be exhausted with a trace going into the oil if coolant level dropped. I am not talking about putting many hours on while watching this and would of course closely monitor.

[Genesis]

.. then ok, but watch it CLOSELY.

I'd be pulling oil samples at 50 hour intervals, and might even go so far as to put 10-20 hours on the new oil, pull a sample, and if that one is clean THEN go the 50.

Yeah, this will cost some money. But if you have a degrading situation here it can go from a small leak to a really big one in a very short period of time, and an overhaul is big bucks, so cheap insurance policies are a good idea...

Its also possible, of course, that the oil was cross-contaminated either before being pulled for the sample or while in the crankcase (e.g. wiping the dipstick with a rag that has coolant on it).

Unlikely, but possible.

Leaks from liner seals frequently don't go into the exhaust at all.

That you have no oil in the coolant is a fairly reliable indication that the oil cooler is not at fault. That's good in one way, and bad in another (always nice to KNOW where a problem is!)

[ezbry]

Genesis, thanks for your much respected advise. Also thanks to all who added comments. This forum has really speeded up my learning process. I have been a silent reader of the forum until now but have gained much knowledge from the sidelines.