What Does Mixed Oil and Coolant Mean

Head Gasket Install

The Function of Oil

Oil is a liquid lubricant that passes through your engine during operation to lubricate all of the engine’s moving parts and reduce friction between the metal components. Without engine oil, the metal pistons and cylinders would scrape against one another, generating friction and accelerating the wear on the engine’s components. Once your pistons and cylinders become worn, your engine will not operate as efficiently, and it may begin to produce excessive blowby, which can contribute to an increase in carbon buildup in the air intake.


The Function of Coolant

Coolant or antifreeze is a liquid that circulates through the engine block to help keep it cool and avoid overheating. If you were running low on coolant or did not have any coolant in the coolant reservoir, your engine would begin to overheat, causing it to run less efficiently and may be causing it to seize up, so destroying your engine. For this reason, it is essential to maintain adequate levels of coolant in the reservoir at all times. In a pinch, you can use water in your coolant system during the warmer months, but you’ll need antifreeze to prevent the water from freezing during the winter. If you did not have a sufficient mixture of antifreeze and water (often a 50/50 mixture), the water in your coolant system could freeze, causing damage to your coolant reservoir, radiator, or possibly the engine block.

What Does Mixed Oil and Coolant Mean?

Causes of oil contamination in the coolant

Leaky Head Gasket. The engine head gasket is a gasket that is installed on the engine block and is designed to seal the engine block to the engine cylinder head to prevent oil and coolant leaks. When a vehicle’s head gasket blows or begins to leak, engine oil can begin to mix with the coolant, contributing to the presence of oil in the coolant. If your vehicle is overheating and you notice oil in the coolant, this may indicate that your head gasket is blown and needs replacement. You can take your vehicle to a shop or purchase a head gasket tester kit online if you want to determine whether the problem is the head gasket. If it is determined that you need to replace your head gasket, unless you are a mechanic or regularly work on engines, you will likely need to take your vehicle to a mechanic for this service, as it requires disassembling the top of your engine to remove the old head gasket and install the new one. The average cost for a repair to replace a head gasket ranges between $1,000 and $2,000.


Oil Cooler

On some vehicles, a factory-installed oil cooler is used to maintain engine oil temperatures at a minimum. If your vehicle’s oil coolers are faulty, this could lead to oil in the coolant. If there is a problem with the oil cooler, the coolant will flow through the oil cooler’s tubes and mingle with the engine’s oil. This might cause significant problems for your coolant system; therefore, it must be repaired promptly. If you are fairly handy and capable of fixing things yourself, you can try replacing the oil cooler to see if this resolves the issue.


Cracked Engine Cylinder Head

Cracks in the cylinder head of an engine can also cause oil and coolant to mix in the engine. Only by disassembling the top end of your engine will you be able to inspect the head gasket and cylinder head to see if the cylinder head is broken. If you observe cracks around the cylinder head, you have the option of either replacing the cylinder head or the entire engine. At that point, it may be cheaper to purchase a used engine from a local scrap yard and have it installed instead of rebuilding the broken engine.



If your engine has been overheating, this could accelerate the head gasket’s deterioration. If your engine’s head gasket has been compromised, oil and coolant will be able to mix within the engine, which could explain the presence of oil in your coolant.


Cracks in the Engine Block

Damage to the engine block can also cause oil and coolant to mix in an automobile. Due to the robust nature of engine blocks, this is the least likely of the possibilities. If your engine block is damaged, you are usually better off scrapping the engine and purchasing a new one. Otherwise, you would need to get a new engine block from a local scrap yard or online to repair your engine so that it functions regularly once again.


Why is oil in the coolant a bad thing?

The presence of oil in your engine coolant indicates that there is a problem with one of your engine’s systems. If oil is somehow combined with your coolant, then your engine oil will be progressively drained from your engine, which can lead to overheating problems or irreparable engine damage.

How to remove oil from coolant

You must first drain all of the old coolant from your vehicle so that there is no longer any old coolant containing oil. Depending on what you believe to be the primary issue, you would then replace the oil cooler or the head gasket.


After completing this procedure, you might next flush the coolant reservoir with fresh coolant and drive your vehicle. If you do not observe any fresh oil accumulation in your coolant, then you have successfully resolved the issue. If you observe oil buildup in your coolant once more, you should investigate the other potential sources and consider replacing or repairing them.