Greenish Oil-What Is It & How To Fix It?

Sometimes you may see greenish engine oil and wonder about it. Have you ever thought about what could be the reason behind this incident? 

In this article, we’ll find the answer to this question. I’ll tell you why your engine oil may look green in color and why it’s harmful to your engine. I’ll also explain the troubleshooting and effective suggestions to keep your engine healthy.

Why Does My Engine Oil Look Green?

Engine oil may look green for different reasons like coolant leak into oil, using fluorescent for leak detection, and the brand of oil you’re using for your vehicle. The first one is bad for your engine and vehicle while the second one is for diagnostic purposes. The green color of the oil because of the brand you’re using is okay.

Engine coolant leakage into the engine is a bad reason to make engine oil look green. If you don’t see any sign of oil floating in the opening of a radiator cap, you may have a coolant leak into the engine oil. The issues could be related to a bad gasket, an internal problem, or a flattened O-ring.

For some diagnostic purposes, your engine oil may change color. In a situation where you are trying to find an oil leak quickly, red dye or fluorescent green dye is added to the oil. This will cause the dye to glow fast and make the leak obvious.  This method is generally used for quick repairs.

Finally, your engine oil may look green just because of the oil brand you’re using for your vehicle. For example, the “Pennsylvania Crude” blends look green naturally. The natural oil base of brands like Brad Penn and Kendall has a green color to it. They are well-recommended and great to use without thinking about why your engine oil looks green.

Also read: Are Mann Oil Filters Good? (Read This First)

Why Is Greenish Oil Harmful to Your Engine?

Mixing coolant and engine oil will make a greenish mixture that is harmful to your engine as it causes several problems like overheating of the engine, excess exhaust smoke, low fuel economy, etc.

Engine oil and coolant are both important fluids for your engine. The coolant maintains the optimal temperature of the engine and the engine oil lubricates the engine so that it can run smoothly. Mixing these two will create malfunctions in the engine and lower the engine efficiency as well as increase fuel consumption. 

Some of the reasons why greenish oil is harmful to your engine are described below:

  1. Engine Overheating 

If the coolant mixes with engine oil, it’ll be difficult for the engine to lubricate as well as cool it properly. Improper lubrication can’t reduce the amount of metal-to-metal frictional contact so much and this produces a large amount of heat. A lack of coolant in the cooling system of your vehicle won’t able to dissipate a significant amount of heat from the engine and this will cause the engine to overheat. 

  1. Excess Exhaust Smoke 

Greenish oil can cause excess smoke from the exhaust. As engine overheating occurs when coolant and engine oil mix, and large amounts of smoke with very high temperatures go through the vehicle exhaust.

  1. Lower Fuel Efficiency

Engine overheating causes poor emissions and drops in fuel economy which eventually leads to lower fuel efficiency.

Also read: How Much is Bentley Oil Change? (the Facts)

How to Troubleshoot the Cause of This Problem?

As greenish oil is harmful to your engine, it’s an important task to find out the causes of mixing coolant and engine oil. Coolant to an oil leak, bad gasket, and issues related to o-ring are some of the most important causes of greenish oil.

So, how can you troubleshoot the causes of this problem? The troubleshooting related to each problem of greenish engine oil is stated below:

  1. Coolant to Oil Leak

Coolant and engine oil are composed of different elements to perform completely different functions. Mixing of coolant and engine oil leads to various problems related to engine overheating that may cause expensive repairs.


  • A cracked head or blown head gasket 
  • Failure of an oil cooler
  • Leaky gasket head
  • Overheating of the engine 
  • Damaged engine block


A proper diagnosis from a professional mechanic can expose the actual reasons behind this phenomenon. Keep calm and call an experienced car engine expert and follow the suggestions and repair plan

  1. Bad Gasket

A blown head gasket is one of the most common reasons why coolant and engine oil mix.  Coolant and engine oil flow in diverse parts of the engine and the function of the head gasket is to seal the coolant so that it can’t enter into the oil pan. A blown gasket will fail to perform its duty and greenish engine oil will form.


  • Overheating of the engine 
  • Pre-ignition and detonation 
  • Abrupt changes in temperature 
  • Following the incorrect procedure of installation 
  • High mileage 
  • Operating in extreme conditions 


To solve the issues related to a blown head gasket, you may need to replace it. The amount needed for the replacement is usually $1,000-$2,000 at least. Another cost-effective but temporary solution is to use a head gasket sealer. Though a head gasket sealer doesn’t give a guarantee of sealing accurately in the long run.

  1. O-Ring Issue

O-ring is one of the most common types of seal which is designed for placing in a groove. It’s a loop of elastomer and inexpensive.  Sometimes they fail or break and need to be replaced. Issues related to o-rings can cause problems related to the mixing of oil and coolant in the engine. 


  • Abrasion in dynamic applications
  • Attack of certain chemicals with elastomers
  • Ingress of media into the elastomer 
  • Forces into the clearance gap due to high stresses 
  • Excessive application temperature 
  • Ultraviolet light exposure on elastomer


Sometimes o-ring doesn’t perform according to expectation but this doesn’t necessarily mean that the o-ring is damaged. There could be a wrong-sized o-ring installed in the system. In this case, you need to change and install the actual-size o-ring. Also, the o-ring can fail due to various reasons and in these kinds of cases, you need to replace the damaged o-ring with a new one.

How to Keep Your Engine Healthy?

The engine is the heart of a car and needs to be maintained and taken care of constantly for smooth functioning for a longer running period. Preventive and predictive maintenance will ensure the healthy condition of the engine. A healthy engine leads to better fuel efficiency, smooth running, larger engine life, and fewer possibilities of engine breakdown. 

Some effective suggestions related to proper engine maintenance are stated below that will eventually help you to ensure a healthy engine for a longer period.

  1. Change engine oil periodically even if your car hasn’t run much.
  2. Maintain a scheduled cleaning or replacement of the air filter based on the situation. 
  3. Inspect the cooling system of your vehicle regularly and replace the coolant if needed. 
  4. Check the fuel and oil filters regularly and replace them if necessary. 
  5. Check for any kind of leaks that may lead to other critical issues of the engine.
  6. Clean and clear the nose of the engine to ensure proper breathing. 
  7. Ensure scheduled inspection and tuning of the vehicle.