What causes engine oil leaks?

Written by roger golden
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What causes engine oil leaks?
Keep your engine clean to make leak detection easier. (New car petrol engines image by Christopher Dodge from Fotolia.com)

An oil leak can be a sign of serious problems with an engine, or it can result from improper maintenance. Depending on the type and size of the leak, engine performance could suffer or the vehicle may not even run. Even a minor oil leak has the potential to become a major problem, and leaks should be located and repaired as soon as possible.

Oil Pan Problems

One very common cause of an engine oil leak occurs when the oil plug is not installed properly. A loose or cross-threaded oil pan plug can leak in varying amounts ranging from occasional drops to a steady flow out of the oil pan drain. A less-common oil-pan related problem results from a damaged oil pan. Typically, this damage comes from road debris that smashes or punctures the pan.

Seals and Gaskets

Gaskets become brittle over time and may wear thin or blow out. The result is an oil leak that may or may not be visible beneath the vehicle. For instance, a blown head gasket may force pressurised oil into the cooling system. The primary characteristic of engine coolant that has been contaminated by oil is a frothy, oily residue in the radiator or coolant reservoir.

Pistons and Rings

Oil can be forced past the rings and pistons, resulting in engine-oil loss. This can be caused by age, excessive engine wear or treatment, poor vehicle maintenance and overfilling the crankcase oil. In this situation, leaked oil may be visible at the exhaust end of the tailpipe, and the exhaust may have a bluish tinge accompanied by a noticeably oily odour.

Cylinder Head

A cracked or warped cylinder head will allow oil to leak, either out of the engine or into the cooling system. Symptoms of this problem include a loss of cylinder compression or an engine that either runs erratically or not at all. Depending on the location of the damage, oil may leak directly out of the engine in a visible manner.

Valve Cover Problems

Loose or warped valve covers will allow oil to leak out between the cylinder head and the valve cover. It may be difficult to tell this condition apart from a loose cover and a blown valve cover gasket, and it may exhibit similar symptoms to a blown gasket or cracked cylinder head. The primary indication is a noticeable oil residue on the engine.

Spark Plugs

A loose spark plug may allow pressurised oil to leak out of the cylinder if the plug is extremely loose or completely missing. Symptoms include a pool of oil around the base of the plug, reduced cylinder compression and a skip in the engine-firing sequence. Additionally, the loose plug may be indicative of stripped threads in the spark plug port, typically indicated by a plug that will not tighten properly or works loose after torque has been applied.

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