4 Causes of Coolant in Oil

4 Causes of Coolant in Oil

When oil and coolant mix in your car’s engine, a milky, colorless sludge forms that is difficult to remove. This contamination of the fluids indicates a mechanical failure that allows the fluids to mix.

Identifying the root cause is key to solving the problem and preventing catastrophic damage to your engine. Here are the most common reasons coolant leaks into oil, what to do, and how much it might cost to repair.

What does coolant look like in oil? As many of you know, oil and water, or coolant in this case, don’t mix. In fact, these two liquids don’t mix even though they’re in constant contact.

When oil and coolant mix in sufficient quantities, a fairly thick sludge forms, usually light brown or gray in color. Many people liken the consistency of this mud to that of a milkshake.

Even in small amounts, coolant contamination in engine oil can be obvious. This condition is often evident by brown specks remaining on your engine’s dipstick, usually located slightly higher than the engine oil itself.

Possible Causes of Coolant in Oil
There are several paths by which coolant can get into your engine’s lubricating oil, and isolating each of these paths requires a thorough diagnosis. Understanding these possible causes can speed up the process of diagnosing the problem at hand.

Here are some of the most common causes of coolant contamination in your engine oil:

#1 – Leaking Head Gasket
The head gasket is used to prevent coolant and oil from mixing at the junction of the engine block and cylinder head. If this seal is damaged, the fluids can no longer mix, creating a path for coolant to get into the engine’s lubricating oil.

#2 – Cracked Engine Block/Cylinder Head
Similar to a leaking head gasket, a broken engine block or cylinder head means that the lubricating oil and coolant can no longer be separated. This creates the potential for cross contamination.

#3 – Damaged Oil Cooler
Some engines use a special heat exchanger called an oil cooler. Oil and coolant can both flow through this radiator, but through separate channels. However, if the oil cooler fails internally, these fluids can come into contact with each other.

#4 – Coolant Accidentally Poured Into the Oil Fill
Some people scoff at the notion of this, but accidentally pouring coolant into your engine is a lot more common than you might think. However, if detected quickly, this is a very easy problem to fix.

What to Do

If this reservoir seems relatively low, further diagnosis is needed. At this point, we highly recommend that you pressure test the cooling system. This will help pinpoint the location of the leak.

It is also important to note that you should never knowingly drive your vehicle with oil contaminated with coolant. If you must drive your vehicle to a repair shop more than a few miles away, you should first drain all of the oil into a drain pan before refilling the engine itself with new oil.

This is not a permanent repair, but it can prevent short-term failure of bearings and other vital components.

Repair Costs

The exact cost of repairing an engine that is leaking coolant into the engine oil supply will vary from case to case. These costs vary depending on the exact cause of the defect as well as the make and model of the vehicle in question.

Generally, you can expect to pay around $1,500 to $2,000 to replace a head gasket, while replacing a cracked cylinder head can easily cost more than $2,000 in total.

At the lower end of this price range is replacing a defective oil cooler. Typically, you can expect to pay around $500 to $700 for such a repair, most of which will go towards purchasing replacement parts. Luckily, the labor costs for such a repair are usually relatively low.

Can I drive a car with coolant in the engine oil? It is never a good idea to drive a vehicle with coolant in the oil. The viscosity of coolant is much thinner than engine oil, so contamination with coolant/antifreeze will reduce the viscosity of the oil. Secondly, it turns out that contaminated engine oil doesn’t protect vital engine components to the same extent as it would otherwise.

This sludge can clog vital oil channels and cause oil starvation. If this occurs, it can cause severe damage to the engine, requiring costly repairs and further downtime.

Whatever the case may be, the root cause of your vehicle’s oil contamination should always be diagnosed and addressed as soon as possible. Doing so may save you a lot of hassle and heartache later.

In many cases, unless you have a lot of experience, this type of repair is best left to a professional mechanic. Make an appointment with an independent mechanic or your local dealer immediately.

What Can Happen if Coolant Gets in Your Oil?
Any form of oil contamination requires immediate attention. This situation becomes even more dire whenever the contaminant in question proves capable of thinning out the oil into which it has leaked.

As a result of this loss in viscosity, engine oil proves incapable of lubricating and protecting an engine’s vital components in the same fashion that it once did. This, in turn, can lead to critical bearing fatigue and failure, severe lifter damage, and undo valvetrain stress. All of these issues are not easily or cheaply remedied.

Coolant in Oil vs Oil in Coolant
Coolant and oil can contaminate one another in two distinct ways. Oil can find its way into an otherwise closed cooling system, or alternatively, coolant can enter an engine’s lubricating oil.

When oil enters an engine’s cooling system, sludge begins to form, often reducing the flow of coolant throughout the system itself. This, in turn, can cause rapid overheating, as well as possible deterioration of vital seals and gaskets.

On the other hand, coolant contaminated oil quickly loses much of its value as a critical lubricant, due to a loss in overall viscosity. This loss in viscosity can quickly lead to bearing, lifter, and valvetrain damage, all of which tend to be quite costly and labor intensive to repair.

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