Signs of Coolant in Engine Oil

by Allen Moore
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Engine coolant mixing with engine oil is a sign of an internal gasket or engine failure. When the coolant mixes with the oil, it robs the oil of its lubricating properties and can destroy an engine rather quickly. In the event coolant is suspected of mixing with the engine oil, the engine should be shut off and not started again until the failure has been corrected.

Coolant Loss

If the coolant level continues to drop, but there are no signs of coolant leaks on the ground or from the exhaust pipe, there is a good chance the coolant is leaking into the crankcase and mixing with the engine oil. A cooling system should not need to be topped off frequently. In fact, adding more than a pint or so at each oil change interval may be indicative of a loss of cooling system integrity.

Sweet Smell

The scents associated with engine oil and engine coolant are distinctly different. While oil has an earthy, musky smell, coolant smells almost sickeningly sweet. In the event coolant loss is evident, but no leaks are seen, pull the engine oil dipstick and take a whiff. If even the faintest hint of sugar hits the olfactory sense, odds are the cooling system is swapping fluid with the engine oil.

The Dreaded Milkshake

When coolant first invades the crankcase and mixes with the oil, it can leave an odd river of green, red or orange in the brown of the oil, depending on the type of coolant the vehicle uses. However, once the engine runs for any amount of time, the crankshaft and oil pump have a blender-like effect on the two fluids, turning them into what many refer to as “the dreaded milkshake." The name comes from the appearance of the well-mixed fluids, which take on the appearance of a milk chocolate shake on the surface. Down below the thinner portion of the mixture is a thick, gooey concoction that resembles a melted milk chocolate bar. The latter mixture gums up engine passageways and is normally indicative of a ruined engine. Once the fluid has had time to mix to this visual consistency, the grit in the coolant has overcome the lubricity of the oil and scoured the bearing beyond repair.

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