What Causes Car Oil to Get Sludge?

Written by michael gunderson
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What Causes Car Oil to Get Sludge?
(Thinkstock/Comstock/Getty Images)

Sludge is a sticky, gel-like substance that coats engine parts and is difficult, if not impossible, to remove. It is the product of oil that has become old and overly stressed. Sludge retains heat, which puts a strain on the engine and other major parts of the vehicle. Signs that a vehicle may have sludge in the engine include loss of oil pressure, failure of other parts of the engine, poor gas mileage and extremely loud noise coming from the engine.

Clogged Engine Passages

Engines are lubricated by oil that passes through the cylinder block of the engine along passageways. The passageways are about the diameter of a pipe cleaner. Once they become clogged with oil, sludge forms, because the oil can no longer flow freely. Thick sludge prevents oil from getting to essential engine parts like the camshaft, pistons and valves.

Carbon Deposits

When engine oil gets old, it loses the ability to function as a lubricant. At that point the oil develops carbon and turns into sludge. The contaminated oil then settles into the engine and moving parts, causing engine failure.

Driving Conditions

Harsh driving conditions like speeding and revving the engine can lead to a build-up of sludge. This raises the temperature in the engine and causes the oil to burn. Oil in this condition is no longer functional and will eventually oxidise and turn into sludge. Frequent driving in stop-and-go traffic and cold starts can also lead to sludge build-up.

Operator Maintenance

Lack of proper maintenance can result in sludge forming in a car's engine. Neglecting to change the oil in a timely manner is one of the primary reasons sludge develops. Using substandard oil or not using the oil recommended by the car manufacturer leads to sludge formation. Not all cases of sludge build-up are the result of poor maintenance. In recent years, the discovery was made that certain vehicles have engines that are prone to form sludge even when timely oil changes are made. Vehicle owners filed class action lawsuits and some were awarded a settlement on their claim that the engine failure did not occur from lack of maintenance on their part.

Preventing Sludge

It is possible to research whether a vehicle is subject to develop sludge. For these vehicles, extra precautions should be taken to protect the engine. Synthetic oils are suggested over conventional motor oil for vehicles that are known to develop sludge. For any vehicle, frequent oil changes are recommended, usually every 5,000 to 7,000 miles. Engine treatments, such as Seafoam, are used after several oil changes to flush out the passages through which oil travels to lubricate the engine.

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