How to Fix Coolant Mixing With Engine Oil?

Written by

Charles Bolte


Vernon Hoppe 

It’s quite common for vehicle owners to experience the issue of engine oil and coolant mixing. Potential reasons for this include a damaged engine block, a warped cylinder head, or a blown head gasket.

We should identify the symptoms to determine the root cause, fix the issue, and replenish both the oil and coolant systems, ensuring no coolant in the oil mixture.

So, keep reading for information on how to fix coolant mixing with engine oil.

Steps to Take When Coolant Mixes With Engine Oil

The coolant mixing with the engine oil can be troublesome. Nonetheless, addressing the issue promptly before it leads to further complications is crucial.

You’ll need basic tools, including:


  • The car manual
  • A flashlight
  • Rubber gloves
  • A container
  • Chemical cleanser
  • Coolant for engine

Here are the steps to take to get coolant out of engine oil:

Step 1: Identify the Symptoms


Oil getting into the coolant tank can occur due to several reasons, each typically signaling a mechanical failure or a compromised sealing component within the engine. Coolant mixing with engine oil can lead to symptoms such as:

  • Milky or Frothy Oil: One of the most straightforward signs is a milky or frothy substance under the oil cap or on the dipstick.
  • Unusual Odors: A sweet-smelling odor from the exhaust or under the hood can signify leaking coolant, which may have mixed with the oil.
  • Overheating Engine: Coolant regulates the engine’s temperature. When it leaks into the oil, it diminishes its cooling capacity, leading to overheating issues.
  • White Smoke from Exhaust: An unusual amount of white smoke from the tailpipe often signifies that coolant has entered the combustion chamber, which could mean it has mixed with the oil.

Step 2: Find out the issue


Understanding how antifreeze can mix with engine oil provides essential insights into the inner workings of an engine and can guide you in troubleshooting the issue effectively.

  • Blown Head Gasket: A blown head gasket is the most common cause of a coolant leak into oil. When the gasket fails, it creates a channel that allows the fluids to mix.
  • Cracked Engine Block: Though less common, a crack in the engine block can also lead to mixing antifreeze and engine oil. Cracks often develop due to extreme temperature changes or mechanical stress.
  • Warped Cylinder Head: A warped or cracked cylinder head can compromise the seal created by the head gasket, leading to the same issues as a blown head gasket.

Step 3: Fix the Issues

The next step is to address the cause of the problem. Here are some things you can do if you encounter any of the above signs:

1. Damaged Head Gasket


When this gasket fails, it creates a pathway for the coolant and oil to mix in engine, leading to problems ranging from constant overheating to complete engine failure.

  • You can purchase a head gasket tester kit from a local shop or online. Utilizing this kit can determine whether or not head gasket is involved in the issue.
  • One of the less expensive methods is using a head gasket sealer. Add this sealer to the radiator while the vehicle idles for at least 50 minutes.
  • You can also try to repair your damaged head gasket manually. This involves disconnecting the negative battery terminal, removing the intake hose airbox, and fixing the head gasket. This method is more hands-on and requires a certain level of technical expertise.

2. Warped Cylinder Head


A DIY method involves using sandpaper, a flat sanding block, flat straight glass, and a thick board to resurface the cylinder head at home. Cutting oil or light oil like WD40 keeps the sandpaper from clogging up with aluminum.

3. Cracker Oil Cooler


If the crack is severe, it might be more cost-effective and safer to replace the oil cooler entirely. You can handle this task by flushing and replacing the old coolant, then, use pliers and 12mm hex to replace the cooler.

How to Drain and Replenish the Fluids


Having oil in coolant reservoir may cause severe damage to your vehicle’s engine and adversely impact its performance. Here are some things you can do to alleviate this issue:

  1. First, you must drain the oil in coolant tank. You can easily do this by removing the drain plug. Prepare a suitable container to place the coolant in.
  2. Add the chemical cleaner to the radiator and add water to the system to remove the residues.
  3. Let the engine run for around 20 minutes for the cleanser to work.
  4. Then, drain the water along with the cleanser and fill the cooling system with water and rerun the egine. Ensure that any small of amount of oil is gone by flushing the system with water. Clear water is an indication that the system is thoroughly clean.
  5. Refill the coolant tank with a new or fresh coolant mixture.
  6. Lastly, ensure the cooling system is in good working condition, and all connections are secure and properly sealed.

What Happens When Coolant Mixes With Engine Oil

When this issue occurs, whether you accidentally put coolant in engine oil or otherwise—the consequences can be severe.

The mixture of these fluids undermines the functionality of the engine’s cooling and lubrication systems, leading to different problems. Below are some key implications of coolant mixing with engine oil:

  • Overheating: Coolant is essential for regulating engine temperature. When diluted with oil, it loses its efficacy in cooling the engine, potentially leading to overheating.
  • Loss of Lubrication: Oil serves to lubricate the engine’s moving parts, resulting in the car not overheating. When contaminated with coolant, the oil loses its lubricating properties. This leads to increased friction, which can cause components to wear down faster.
  • Reduced Engine Efficiency: The inability of contaminated oil to lubricate and of compromised coolant to cool effectively means that the engine must work harder to produce the same output, reducing its efficiency.
  • Engine Damage: Prolonged exposure to contaminated oil and coolant can lead to severe engine damage, including warped or cracked components, which can necessitate expensive repairs or even complete engine replacement.


The issue of coolant mixing with engine oil is a serious mechanical problem that requires immediate attention to prevent further damage and potential engine failure. The adverse effects on engine performance and longevity underscore the urgency of resolving this issue.

Suppose you need assistance on how to fix coolant mixing with engine oil. In that case, it’s best to consult an experienced mechanic who can assess the damage and recommend the most effective solution.

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