Antifreeze In Oil – Means Your Engine Is Leaking Internally

Antifreeze In Oil - Means Your Engine Is Leaking Internally
Antifreeze In Oil - Means Your Engine Is Leaking Internally

Antifreeze In Oil, is a sign of an internal leak. And, is usually caused by, a bad gasket or engine failure.

When Antifreeze mixes with Engine Oil, it robs the Oil of its lubricating properties and can destroy an engine.

So, Antifreeze In Oil, creates a light brown liquid, that looks an awful lot like, chocolate milk.

Above all, if you notice this on the dipstick, you have Antifreeze In Oil. Subsequently, stop driving if you can, and have it checked as soon as possible.

So, Antifreeze and Engine Coolant are similar, but not the same. Antifreeze is a concentrated, glycol based liquid, that must be, diluted with water before use. And, then it is referred to as, Engine Coolant.

Consequently, when Antifreeze mixes with Engine Oil, it make the oil thicker. As a result, making it harder to flow through the oil galleries and lubricate the engine.

Antifreeze In Oil
Antifreeze In Oil

Also, Antifreeze has almost no lubricating properties, when mixed with Engine Oil. Antifreeze In Oil, causes a thickening of the lubricant, thereby increasing the oil viscosity and reducing the flow.

Another reason why, Antifreeze In Oil damages the engine, is that it creates an acidic environment, within the Oil.

Organic acids will form and can jeopardize, Engine Bearings and other frictional surfaces.

Engine Bearing Corrosion Damage
Engine Bearing Corrosion Damage

The corrosive conditions, can pit the clad surfaces of the lead/tin overlay of the Engine Bearings. So, even a small coolant leak over time, is enough to severely corrode engine steel and copper surfaces.

Internal Coolant Leaks (hidden inside the engine)

Head Gasket Leak

Head Gasket Leak
Head Gasket Leak

Internal coolant leaks are most often, due to a bad head gasket. So, a bad head gasket, may leak coolant into a cylinder or into the crankcase. Consequently, coolant leaking into the crankcase, dilutes the Engine Oil. And, can damage the Engine Bearings in your engine. A head gasket leaking coolant into a cylinder, can foul the spark plug. And, create a lot of white smoke out the exhaust.

Head gasket failures are often the result of, engine overheating. Because, of a coolant leak, a bad Thermostat, or an Electric Cooling Fan not working. When the engine overheats, thermal expansion can crush and damage, portions of the head gasket. This damaged area, may then start to leak combustion pressure and coolant. Finally, causing Antifreeze In Oil.

Intake Manifold Gasket Leak

Intake Manifold Gasket Leak
Intake Manifold Gasket Leak

In addition, the gasket that seals, the Intake Manifold to the cylinder heads may leak. Furthermore, this could allow coolant to enter the intake port, or the crankcase. Some engines, such as General Motors 3.1L and 3.4L V6 engines. And, also, 4.3L, 5.0L and 5.7L V8s, are famous for leaky Intake Manifold gaskets. And, is a common cause of, Antifreeze In Oil.

The Intake Manifold gaskets, on these engines are plastic and often fail at 50,000 to 80,000 miles. Other problem applications include, the Intake Manifold gaskets on, Buick 3800 V6 and Ford 4.0L V6 engines.

Antifreeze, can leak into Engine Oil and other Lubricating Oils, in a variety of ways:

  • Defective or damaged seals.
  • Blown, head gaskets.
  • Improperly torqued head bolts.
  • Thermally warped or cracked, cylinder heads.
  • Cracked block or cylinder head, from frozen Engine Coolant.
  • Improperly machined, head and block surfaces.
  • Corrosion damage of cylinder liners.
  • Cavitation, erosion, corrosion of cylinder liners.
  • Electrochemical erosion.
  • Damaged or corroded, cooler cores.
  • Water pump seal failure and weep-hole blockage.

The chain reaction then gains new life, as the detergents and dispersants, come in with the new Engine Oil. This now begins to, mobilize the sludge and deposits. Then, within minutes after an oil and filter change, the new filter can, become plugged again.

Following, is the summary of this chain reaction:

  • Firstly, coolant leaks, into the crankcase oil. (Antifreeze In Oil )
  • Acids and precipitants form, as the additives in the Engine Coolant and Engine Oil react.
  • Hence, these insolubles, begin to plug the Oil Filter.
  • Concurrently, the acids and water, disrupt soot dispersancy, causing a dumping condition.
  • More sludge and insolubles form.
  • By now, the filter is plugged with the glycol transformation by-products.
  • The oil and filter are changed.
  • Typically around 15 percent of the old oil remains, either in the oil pan or on engine surfaces.
  • The new oil (with detergents and dispersants) mobilizes the soot and the sludge, carrying it to the filter.
  • Once again, the filter becomes clogged. As a result, leading to Antifreeze In Oil. (even with the coolant leak fixed)

Antifreeze (Glycol) Types and Colors

Antifreeze (Glycol) Types and Colors
Antifreeze (Glycol) Types and Colors

Years ago, when your cooling system was low, you popped the Radiator Cap off. And, added your favorite brand of Antifreeze. Usually, green or yellow and off you went. Now, it’s just not that that easy. Because, almost every car maker has come out with, their own blend of Antifreeze. Many of these are, long life and they come in, a whole rainbow of colors.

Contaminated Brown Antifreeze
Contaminated Brown Antifreeze

Why your coolant may look brown:

  • Contamination, from rust or poor water.
  • Orange coolant, is again and again, topped up with green, gold or yellow.
  • A coolant contaminated, by sealants or other additives.
  • Antifreeze In Oil.


So, when adding Antifreeze to your system, make sure you match, what is in there already. Although, you can safely flush the system and use, the old standby green Antifreeze. But, you don’t want to mix them. Finally, a 50/50 mixture of whatever you use, is critical for engine corrosion protection.

Thank You !