Sometimes you will notice milky oil in the boat engine. What is the cause? How do you go about it? And how do you prevent it from happening.

These are the three crucial questions most boat users ask.

When oil is mixed with water and gets inside the engine, it will automatically assume a milky appearance. But you should be able to tell how the water got mixed with oil in the first place.

Milky oil in boat engine can be caused by a few underlying factors. 1. An open or missing thermostat 2. A damaged or scored cylinder walls 3. Blown gasket and 4. Damaged piston rings.

These are the few causes of oil getting mixed with water in the engine.

Luckily, with this guide you will understand what to do when this situation occurs and how to prevent future occurrence.

Here is a detailed guide to further explain this.

Why Is My Outboard Oil Milky?
There are four reasons that can cause the outboard motor to have milky oil appearance.

1. Open thermostat
2. Blown gasket
3. Damaged cylinder walls
4. Damaged piston rings

Open Thermostat
Ordinarily, when the thermostat is open or damaged, condensation will automatically occur.

Condensation occurs when heat from the engine meets cold water droplets from the water pump. The constant heating and cooling will cause condensed air to form inside the outbound engine and mix with the oil. Thus a milky substance.

Damaged piston rings
When the piston rings are damaged, oil will find its way into the combustion chamber. Inside the combustion chamber, there is fuel and carbon.

The fuel will mix with the oil and thus a milky substance will be formed after a while.

Blown gasket
A blown gasket will allow small amounts of water to sip inside the engine head.
When the pistons ascend and descend, water will be sucked inside the combustion chamber. That’s not all, the water will sip deep down into the piston rings and finally to the oil chamber.

After the water is mixed with oil, it will form a milky substance.

Damaged cylinder walls
When the cylinder walls are damaged, small amounts of oil will flow through the damaged walls into the combustion chamber. Also, exhaust and fuel will flow past the cylinder walls and mix with the oil to form a milky substance.

These are the four most common reasons to answer your problem.

How to Flush Milky Oil Out of Engine
It is advisable to flush the engine after you notice milky oil. Usually, there are a few simple steps to you need to follow to flush the milky oil from the engine block.

Step 1: Have necessary tools and utilities ready
Note that used oil can cause a big mess when it spills. So, you need to wear the necessary safety gear and use the correct tools. Also, you should prepare the work area.
- Wear a pair of latex gloves
- Use engine flush non-solvent additive

Step 2: Open the oil plug
After you have everything set in place, open the oil plug inlet with a spanner or socket wrench and add engine flush additive. About 100ml is enough. The engine flush non-solvent additive will help break down the carbon deposits from the old contaminated oil.

If you do not put the flush additive in the engine, you will not flush the entire milky oil from the engine. Hence, you will still find that there is a milky substance in the oil after a while.

Step 3: Warm the engine
The next step is to warm the engine (with the engine flush solvent inside). Warming the engine will allow the oil to break down and flow smoothly as you drain it.

Also when the engine is running, the flush solvent will completely circulate inside the engine.

Turn the engine ON and allow it to run for approximately 6 minutes. If it is a larger engine model, you should allow it to run for approximately 10 to 15 minutes.

Step 4: Prepare a can to hold the oil
Look for a sizeable can that can hold the milky oil.
Ordinarily, an outboard motor holds about 4 liters of oil. But larger outboard engines can hold up to 8 liters of engine oil.

Put the can under the sump pump. This is where the drain plug is normally located.

Step 5: Open the outboard oil drain plug
The location of the outboard drain hole is, however, placed in different spots. Therefore, you should check the engine’s manual to get the exact spot where the drain plug is located.

In most cases, it is concealed within the engines back side with a matching-color plastic casing

Step 7: Flush the milky oil
Next, drain the milky oil from the outboard engine block.

Here, you need to allow the engine to sit in a slanted vertical position to allow sufficient flow of oil. Make sure that all the oil is drained from the engine to avoid future milky oil recurrence.

Step 8: Change the oil filter
Finally, you need to change the oil filter before you pour fresh engine oil into the outboard motor. Remove the old filter with a Swivel-Gripper filter wrench and replace it with a new model that is compatible with the boat’s engine.

Conclusion
Most boat owners will encounter significant challenges along the way. Among these challenges can include a worn out gasket or a damaged cylinder head. These are among the most common causes of milky oil we have talked about.

These issues among others, in most cases, are the cause of milky oil in the engine. Water will mix with the pure oil and cause a milky appearance. But if you want the engine to run smoothly, you should know what to do when this kind of situation occurs. Also, you need to understand all the steps required for successful outcomes.
Fortunately, with this guide, you have now understood that water and contaminated residues are the most common causes of milky engine oil.

Know how to correctly flush an outboard engine to get rid of the milky oil.