Rick's Free Auto Repair Advice

Oil in coolant

What causes oil in the coolant?

Oil in coolant is an indication of a serious failure in either the engine, transmission cooler, turbo or oil cooler. Let’s take a look at how oil gets into the coolant in the first place

Head gasket failure can result in oil in coolant

Oil and coolant flow through the engine block and into the

head gasket leak

Typical head gasket

cylinder head to cool and lubricate the cylinder head components. The head gasket seals the passages so there’s no cross-contamination as those fluids flow from the block to the head and back to the block. However, if the engine has experienced an overheat condition where the cylinder head warps, the gasket can fail and allow oil to flow into the coolant and vice versa.

Neglecting oil changes and coolant changes can also cause gasket degradation and actual metal degradation around the coolant and oil passages, allowing the two fluids to mix

The only fix for oil in coolant contamination is to flush the entire cooling and oil system, fix the head gasket failure and install new coolant and oil

Crack in the block or cylinder head can result in oil in the coolant

Just like a damaged head gasket, cracks or porosity in the engine block or cylinder head can result in oil entering the cooling system and vice versa. In that case, block repair or porosity fixes are required.

Failed transmission cooler can result in oil in coolant

Transmission fluid lubricates transmission components and transmission oil cooler in radiatorcarries away heat caused by friction. To keep transmission fluid cool and remove heat, the transmission pumps hot fluid into a transmission heat exchanger located in the bottom tank of a downflow radiator or in the exit tank of a crossflow radiator. Hot engine coolant leaves the engine at approximately 190°F to 210°F before it enters the radiator. Depending on the size of the radiator, ambient temperature, speed, and size of the water pump and radiator fan, the radiator can reduce coolant temperature by at least 10°F to 30°F degrees (more in cooler weather).

Hot transmission fluid is approximately 200°F to 260°F, depending on the condition of the transmission. When cooled, the ideal transmission fluid temperature is 175°F which can be accomplished easily in a normally operating cooling system.

However, If you neglect cooling system maintenance, corrosion in the radiator can degrade the transmission cooler to the point where it fails and transmission fluid enters the coolant. Worse yet, coolant enters the transmission, eventually destroying the transmission.

Keeping transmission fluid cool is very important to long life. In fact, a constant 20°F reduction in transmission fluid temperature can double the life of the transmission.

If you have transmission fluid in the coolant, you must flush the entire cooling system, replace the radiator, flush the transmission and refill with new fluids.

Failed oil cooler can result in oil in coolant

Newer engines fitted with turbos often contain an engine oil turbo oil coolercooler to remove heat from the oil as it leaves the turbo. Turbos operate at extreme temperatures and high speeds, so a constant supply of cool oil is critical to their lifespan. An oil cooler consists of many winds of tubing submerged in coolant that has just been cooled by the radiator. If you neglect cooling system maintenance, corrosion can degrade the oil tubing, caused oil to flow into the coolant.

To fix that kind of breach, you much flush the entire cooling system, replace the oil cooler and refill with fresh fluids.

Failed turbo can result in oil in coolant

Coolant runs through the turbo to remove heat. Seals inside the turbo prevent cross-contamination of coolant and oil. A failed turbo can result in oil in the coolant. In this case, the fix involves replacing the turbo and flushing the entire cooling system.

©, 2020 Rick Muscoplat


Posted on by Rick Muscoplat

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