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Milky Oil & Its Dangers

Mar 31, 2023 ·

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If you notice milky oil in your engine, get it checked out right away!

Milky oil can indicate a number of engine problems and is most commonly found on the underside of the oil cap during an oil change. The good news is that with proper maintenance and care, this engine defect can usually be prevented and fixed.

Students can practice engine servicing fundamentals taught through automotive courses by enrolling in Universal Technical Institute's (UTI) 51-week Automotive Technology training program.By developing these skills, UTI graduates can prevent all sorts of engine defects, including milky oil!

Stay tuned to learn more! We'll go over how milky oil can cause engine failure and how to repair and prevent it.

What Is Milky Engine Oil?

Milky oil, as the name implies, is typically milky white or light brown in color. It's also thicker than typical engine oil and is formed when motor oils react with moisture, usually due to coolant contamination or condensation on engine components.

Read: Main Components of a Car & Their Functions

Milky Oil Causes

There are multiple ways moisture can enter an engine system and its components. After that, it can mix with the oil contained in the engine and form milky oil.

Faulty Head Gasket

The primary function of the head gasket is to seal the combustion chamber, separating and containing the gases and liquids inside. If this seal fails, coolant and engine oil can mix and produce milky oil.

Sludge Buildup

When an engine sits idle for an extended period, sludge can form in the crankcase. Once the engine is restarted, the sludge buildup can mix with regular oil causing it to become milky.


In humid climates and during weather changes that rapidly increase humidity levels, a higher concentration of airborne water molecules can enter engine components such as oil seals and gaskets. Moisture is then absorbed by the oil as it comes into contact with these components, resulting in milky oil.

Read: Advancing vs. Retarding Ignition Timing: Everything You Need to Know

Dangers of Milky Oil

Milky oil can cause significant engine wear and damage in the following ways:

  • Corrosion: Corrosion can cause moisture to enter the system and produce milky oil, which can then produce rust. Rust corrosion can accelerate engine wear, reduce performance and eventually cause engine failure.
  • Clogged passageways: Milky oil's thick consistency can clog an engine's vital lubrication pathways. As a result, engine components cannot be adequately lubricated and are more likely to develop blockages, which can prevent proper engine oil circulation.
  • Diminished cooling: Blockages can also insulate heat, which can cause engine components to burn out and reduce their longevity.
  • Poor lubrication: A higher moisture content reduces the effectiveness of engine oil lubrication. This can result in metal surfaces grinding against one another and producing tiny particles that clog passageways and damage parts over time.
  • Increased operational costs: The longer the underlying issue of milky oil isn’t addressed, the higher these service costs eventually add up as the components continuously degrade.

Read: Automotive Shop Safety Rules

Fixing Milky Oil

Diagnosing the cause of milky oil can be tricky. However, the earlier a diagnosis is made, the easier it is to resolve oil contamination.

1. Determine the Cause

Look for milky residue on the dipstick, in the crankcase, down the side of the engine block or on the underside of the oil filler cap. These could be signs of an external coolant leak or water contamination. Then, look for milky-looking droplets, sediment or streaks in the engine crankcase.

2. Fix the Issue

If the oil looks milky, address the underlying issue as soon as possible. This could mean replacing corroded pipes, clearing any blockages or dealing with any of the other potential issues mentioned above.

2. Flush the Engine

Use an engine cleaning solution to flush the engine. Then, fill it with clean, new oil.

3. Change the Oil

After flushing your engine, replace the oil and filter as needed. To ensure the engine is properly lubricated, use the proper grade and type of oil according to the manufacturer's recommendations.

Diagnosing and fixing milky oil requires technical knowledge, as well as precision and adaptability. Because no auto mechanic's career is without challenges, Technicians must be prepared to have their technical aptitude tested when they face challenges like milky oil formation!

These skills can be learned in a program like UTI's 51-week Automotive Technology program, which provides instructional support and resources to help students refine their automotive capabilities.

Read: The Most Common Car Cooling System Problems

Preventing Milky Oil

Regular maintenance is key to keeping any engine running smoothly. It can keep excess moisture from contaminating your engine's components and causing milky oil to form.

1. Correct Engine Oil Usage

Always check and abide by the engine manufacturer's oil viscosity requirements. This way, your motor oil will properly lubricate your engine components with minimal risk of blockages.

2. Regular Oil Changes

Change the oil and filter in your engine according to the manufacturer's recommendations. Otherwise, old oil can degrade and mix with moisture over time, resulting in milky oil.

3. Avoiding Frequent Cold Starts

Condensation can form on engines that haven’t been running for a while. When vehicles are restarted, this extra moisture can result in milky engine oil. Some of the most effective ways to avoid cold starts are to keep vehicles in heated garages or to use block heaters.

4. Close Inspection of Hoses and Gaskets

During routine inspections, every engine component should be assessed. However, pay particular attention to signs of wear or fluid leakage on the ground and in your hoses and gaskets. If the leakage isn’t addressed properly and promptly, air and moisture can otherwise enter the engine and form milky oil.

An automotive mechanic school like UTI can prepare its students to perform industry-standard maintenance and properly prevent milky oil! This training enables them to practice engine servicing while also earning credentials that may be valued by employers in the industry.

Read: What is Battery Terminal Corrosion?

Don’t Let Milky Oil Endanger Your Auto Tech Projects!

As an automotive technician, it's critical to understand engine issues like milky oil and how to properly address their underlying causes. Come back to this guide if you ever need to remember how to do exactly that!

Learning the skills required to service automotive engines is critical for aspiring automotive technicians. That is why students at UTI can enroll in our 51-week Automotive Technology program, which teaches engine servicing skills, including those that help technicians diagnose and repair engine problems like milky oil! This program is offered at 13 Universal Technical Institute locations across the country, including our Florida campuses in Miramar and Orlando.

To learn more about our automotive technology curriculum, request more information. Submit an automotive trade school application to start learning!

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