Coolant in Oil: Causes, Symptoms, and What To Do

Written by

CarParts.com Research Team

Automotive and Tech Writers

Updated on October 24th, 2024

Reading Time: 3 minutes
Summary
  • Engine coolant can only mix with oil if your engine or oil cooler has an issue. If you find coolant in your engine oil, you should be immediately concerned because it will compromise your oil’s ability to lubricate and cool your engine.
  • Motor oil should have a golden or amber hue. If there’s coolant in the oil, then it will look like chocolate milk. Other signs of coolant mixing with engine oil include white smoke from the exhaust and sweet-smelling exhaust fumes.
  • If you’ve noticed the previously mentioned symptoms, then you shouldn’t drive your vehicle further. Otherwise, you risk causing excessive wear out or overheating your engine. You should immediately head to a mechanic to have your vehicle diagnosed and repaired.

Have you noticed the presence of coolant in your engine oil? This is a serious issue that can seriously damage your engine. Engine oil and coolant circulate through distinct channels in your engine. Oil and coolant should never mix. These two liquids can only mix when something goes wrong in your engine or oil cooler.

Engine oil is crucial for maintaining engine function because oil lubricates components and prevents excessive wear. The presence of coolant is going to compromise the motor oil’s lubricating properties, potentially causing extensive engine damage.

What Are the Symptoms of Coolant Mixing With Engine Oil?

You might have discovered coolant mixed with your engine oil because the oil on the dipstick has changed color. What does coolant in oil look like? The coolant in oil makes it color brown, similar to chocolate milk. Motor oil should have a golden or amber hue. Other signs of coolant mixing with engine oil include white smoke from the exhaust and sweet-smelling exhaust fumes.

Another sign of coolant mixing with your oil is low coolant levels. If your coolant reservoir is empty and there are no signs of leaks, you should check your engine oil. Without coolant flowing through the engine’s channels, your engine can overheat.

How long can you drive with coolant in the engine oil? It’s hard to say how long an engine can run with this issue. Your engine is likely going to wear out excessively as soon as coolant is introduced. However, it’s unclear how long it will take until the engine gets damaged to the point that it overheats or shuts down.

What You Should Do After Discovering Coolant in Oil?

If you’ve noticed the previously mentioned symptoms, then you shouldn’t drive your vehicle further. Otherwise, you risk wearing out or overheating your engine, which can cause major engine damage and expensive repairs. You should immediately head to a mechanic to have your vehicle diagnosed and repaired.

The repair will involve draining all the coolant and engine oil from your vehicle to remove all the contaminated fluids. Afterward, the oil and coolant channels must be flushed to remove the remaining contaminants.

A blown head gasket, a cracked cylinder head or engine block, or faulty engine gaskets or seals are the most common causes for coolant to mix with engine oil. These issues will need to be resolved before your engine can be filled up with fluids and started. Otherwise, the fluids will continue mixing.

The repair process of fixing these components is going to vary for each vehicle model. Follow the steps in your vehicle’s repair manual or have the task done by a professional.

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How Does Coolant in Oil Affect Your Engine?

When coolant and engine oil mix, several things are going to happen:

Reduced Lubrication

Coolant mixing with the oil will make your vehicle’s oil turn into a gel, which will reduce oil flow inside your engine. Coolant will also affect the oil’s ability to lubricate engine components.

Increased Abrasion and Engine Wear

Contaminated oil is going to absorb more soot from combustion. Oil is formulated to absorb the soot that the engine generates using various additives. The additives also disperse the soot, which means the soot doesn’t clump together and create abrasive particles. However, coolant will affect the oil’s ability to disperse the soot, increasing abrasion and component wear.

Aside from soot, abrasive oil balls will also form when coolant mixes with oil. These tiny oil balls are 5 to 40 microns in size and they can erode engine surfaces such as cylinder walls.

Engine Corrosion

Glycol in coolant also breaks down in the high temperatures present in the oil passages, forming glycolic acid. This substance corrodes certain metals in your vehicle’s engine, forming metal salts.

Coolant in engine oil is an indicator of a serious engine problem. If you notice signs of coolant in your oil, you should stop using your vehicle and seek professional help immediately. You can prevent further damage and ensure your engine’s reliability as long as you promptly respond to symptoms and address the root cause immediately.

Written By CarParts.com Research Team

Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.