Lost without a clue: Saltwater in oil

[pbmaise]

Well this was a real eye opener. A fresh water coolant leak can result in saltwater in the oil pan.

The first photo shows the engine with the large "radiator" and coolant reservoir. What I am calling the radiator is the large grey box on the port side of the engine with a radiator filler cap above. Inside this box is an exhaust manifold that receives the hot exhaust gases from the engine and cools them down before exiting out the side. Without this cooling box, the exhaust manifold would get red hot and be a serious danger to the crew.

The second picture is a detail picture of the side of the box. The center round pipe is where cooled but still very hot exhaust gas exits the box. Coolant resides in the box above and below the pipe. The coolant exits the radiator at the bottom and heads to the engine.

The third photograph is the pipe that carries the exhaust gas down to the "muffler" aka saltwater lifting box. The point at which saltwater is injected into exhaust stream is what I term the mixing elbow. I again apologize to all those who I confuse with my terms.

The fourth photograph shows the large newly painted red exhaust lifting tank aka muffler. Notice new flexible exhaust hose that rises above it, turns, and then exits the boat from the side. There is no anti-siphon. In order for a siphon to occur the outlet would need to be continuously below the water line. Since my vessel doesn't heel and the outlet is above the waterline any water in the line drains out. That condition can obviously occur when a vessel heels, which isn't applicable in my case.

This is really the only type of engine I am familiar with. I did follow the helpful links someone posted for marine exhaust systems and saw nothing similar to my configuration.

Okay, now that I have explained the photos lets get into the details as to how a coolant leak resulted in saltwater in the oil.

#1 The person that assembled the exhaust system bolted applied a gasket compound to the flat surfaces seen in photo 2 and then bolted on the pipe with the mixing elbow. There was no gasket just the gasket compound.

This arrangement worked for many years. However, there were two minor flaws.
A. I highly suspect the two pipes are different metals. The pipe with the mixing valve is most likely 304L. The manifold pipe is most likely a lower grade.
B. The gasket compound has a lower temperature limit than an actual asbestos gasket.
C. The major flaw appears to be the location of the mixing elbow. It is not that far from the manifold pipe intersection.

#2 The flexible exhaust hose, seen in photo used to rise up all the way to the ceiling of the engine room. Obviously, someone thought the higher the loop the better. As I stated before, I at one point became worried that this high loop was causing too much water to remain in the system after engine shutdown. So I would close the raw water supply valve, wait a few seconds and then turn off the engine. My hope was I was purging sea water out of the line.

#3 When we took apart the exhaust system. We found large crystals of salt in the exhaust manifold pipe. I am not exactly sure how they got there.
a. Yes the mixing elbow is fairly close, however, the elbow is pointing injected seawater away and positive pressure from the exhaust should push any mist out of the manifold pipe.
b. It might be possible enough water remained in the exhaust to splash up into the exhaust pipe and gradually build up a salt layer. In fact, I do know for sure that in 2010 while crossing the Pacific, that water did splash in this fashion for several days. So these salt deposits may have been in the pipe a long time.
c. I might have been correct with my concern that too much water remained in the exhaust system and this was just enough to cause salt deposits.

#4 Whatever the source of the salt, that salt seems to be the direct cause of a small hole we found in the exhaust manifold. At first, this hole was not large enough to cause anything more than a gradual drop in coolant level. Coolant would leak into the hole, flow out of the engine and down into the muffler.

Aside: Most experts suggest that a manifold will have a life expectancy of six to eight years. However, heavy use in saltwater can see this drop to as low as three years, while lightly used freshwater boats can get up to 20 years out of a manifold. I am pretty sure this is the original manifold when the vessel launched over 20 years ago. Therefore, we were certainly over due for a problem with the manifold.

#5 After the vessel purpose switched from private cruising yacht to commercial day charters, the coolant leakage rate became greater and there was one major coolant leak incident when a rubber hose failed. An external reservoir was added in the engine room to keep up with the loss of coolant.

#6 When saltwater began showing up in the oil, we in correctly assumed the problem was caused by seawater entering the engine. That wasn't the case. It was coolant mixed with seawater and salt dissolved off the walls of the manifold. Coolant first entered the manifold, drained down into the muffler, mixed with seawater, and then gradually filled the entire exhaust system. After the exhaust system was full, the coolant, that kept coming owing to the external reservoir, eventually entered the exhaust manifold, then the engine and finally the oil pan.

Note: This problem went largely undetected as long as the engine was run daily. After the Covid 19 outbreak, the vessel didn't need to go anywhere, so the coolant leak had enough time to fill the exhaust system.

Other notes:
A. We took apart the exhaust system after someone suggested the lifting tank could have been blocked. We learned it was whistle clean. We also disturbed it enough to learn there was a small leak in one of the welds. This was repaired and it was put back together.

B. We also learned that the exhaust hose was rotten. It was replaced with a new hose and the loop height was reduced to help reduce the amount of water left in the lifting tank after the engine is shut down. This also reduces some protection from high seas. Therefore, if the vessel goes on a high seas crossing this hose should be reduced.

C. During final assembly, we installed an asbestos high temperature gasket to help provide a better seal that the previous sealing compound. It is rated for a temperature of 390. Enough spare gasket material was purchased to easily replace it if the engine is ever run dry again.

D. One new concern is that exhaust manifold. Should a hole develop in that manifold again in a spot difficult to repair, the whole manifold and cooling box may have to be replaced. Getting a replacement box may be quite difficult and I am recommending we try and locate a whole new box and keep it as a spare.

Once again thank you for everyone's assistance on solving this problem.

[mvweebles]

Manifolds tend to be expensive. This one with it's integral expansion tank is probably difficult to source too. Just a hunch. If/when time comes, you will probably have to have a replacement fabricated or repair this one. Totally agree that if you find a spare, buy it.

From your description, it sounded like you were thinking the vented loop goes in the exhaust hose, perhaps after lift muffler. If so, that is not correct - it would go in the raw water inlet into the mixing elbow (see pic below). If the engine is anywhere close to being below waterline, a siphon break is strongly recommended. Maybe someone else with more advanced mechanic' skills can comment on whether this particular configuration bypasses the need, but given that a vented loop would be an inexpensive add-on, you might want to consider.

The exhaust hose should have a continuous downhill slope from the top of the loop coming out of the lift muffler.

Thanks for the update. Always good to hear the end of the story.

Peter