What Can Cause an Oil Leak?
Gaskets, O-rings and seals due to heat pressure and age. Shrink and harden this produces the perfect environment for an oil leak.
Sump Pans & Plugs
The sump plug, oil filter and rocker valve gasket are most likely to fail. If the sump pan is damaged or the sump plug becomes worn or loose, oil will be lost; this would result in excess oil consumption or even engine failure. Sump plugs should be changed regularly and sump pans replaced if damaged.
This is the cheapest repair of an oil leak that you are likely to encounter, and it is recommended that you purchase at least one sump plug as a spare.
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The sump pan, directly below the engine block, collects engine oil that has been pumped around the engine. The sump plug is a bolt at the base of the sump pan that is unscrewed to allow oil to be drained.
You may have heard of wet sump and dry sump systems, but what’s the difference? The vast majority of cars use the wet sump system, in which all of the engine’s oil is collected in the sump pan before being recirculated around the engine.
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The dry sump system is generally restricted to professional racing cars that require the highest amount of power and engine-oil control. The difference with this system is that the oil is pumped out of the sump pan to be stored in a separate tank before it is redistributed around the engine by an external pump – leaving the sump pan ‘dry’. This system has a number of advantages to top-level racers, including less weight on the rotating assembly, more space for the rotating assembly to spin, higher oil capacity and increased oil pressure.
Because the sump pan hangs down below the engine, it can easily be damaged by loose debris or speed bumps. If this happens to your vehicle, it must be replaced as soon as possible.
The most common cause of gasket and seal failure going too long between oil changes causing oil to break down, allowing old oil to become contaminated from condensation and combustion by-products. Once saturated with contaminates, acids develop in the oil. These acids attack and degrade gaskets and seals, leading to oil leaks. Always have any leak checked out by your mechanic. Repairing leaks will save you from costly repairs down the road.
Gaskets, Seals and O-rings
Gaskets and seals are designed to keep oil in your engine where it belongs, while keeping out dust, dirt and moisture that lead to oil breakdown and premature engine damage.
These gaskets and seals will leak oil if they fail. Here’s where you’ll see the leaking oil:
- Rocker (valve) cover gaskets: Look for dirt and gunk buildup at the top of the engine and small puddles of oil around the cylinder head indents and spark plugs. Also check for oil spots or drip stains under the center of the engine, as well as a burning oil smell. These leaky gaskets are a common cause of an oil leak and are easy to identify and repair yourself.
- Front and timing cover gasket and seal: You’ll see oil leaking from the front or center of the engine.
- Front main seal, timing cover gasket or seal: When these seals or gasket fail, you’ll see oil slung all over the drive or timing belt.
- Rear main oil seal: If the top of the engine is dry, you’ll see oil dripping from between the engine and transmission, and the flywheel is covered in oil. In this case, removing the transmission inspection cover is necessary to confirm the leak.
- Camshaft seal: Located at the rear of the cylinder head, a bad camshaft seal will leave oily residue below the rocker cover.
- An oil pan gasket: This gasket can leave drops anywhere under an engine, which means diagnosing a bad oil pan gasket can be tricky. Oil from just about any other leaking engine gasket or seal will drip over the oil pan. It’s important your mechanic verifies the leak is from the oil pan gasket and not just oil from a different source.
- Oil filter adapter mounting gasket: If you see oil dripping from the oil filter area, check the filter and the filter mounting adapter gasket. Over-tightening can not only damage the oil filter gasket, it can damage the adapter gasket as well.
- Head gasket; Although rare, a head gasket can cause an external oil leak and is often misdiagnosed as a rocker cover or camshaft seal leak. More likely, you’ll see white smoke coming from the tailpipe signaling coolant from a bad head gasket is burning in the combustion chamber.
- Dip stick tube O-ring: A dip stick tube that is loose, wobbly or cracked can result in a significant oil leak. If your dip stick is loose, or its mounting bracket is broken or missing, make it a priority to get it repaired so that you can check your oil.
Other Causes of Oil Leaks
- Oil pressure sending unit. Oil sending units can commonly cause a slow leak or, because they are screwed directly into the engine’s oil pressure system, a gusher. A telltale sign that an oil sending unit is failing will be the oil light flashing, or erroneous oil pressure readings. On newer cars, a bad sending unit can send false low oil pressure data to the engine computer, which in turn will shut off the engine for no apparent reason.
- Oil pan: The oil pan can leak if road debris or driving over a curb has caused a puncture.
- Oil pan drain plug: Over-tightening the oil pan drain plug or oil filter during an oil change can crush the gaskets, creating a gap for oil to leak out. Over-tightening the oil pan drain plug can also strip the threads on the drain plug. Replacing the drain plug is a simple fix, although you may need all new oil. However, if the threads inside the oil pan are stripped, then you’re looking at re-tapping the thread or replacing the sump pan.
- A bad, stuck or clogged PCV valve: This can cause all kinds of headaches. One is increasing internal engine pressure, which results in the failure of one or more engine O-rings, gaskets or seals.
- Improper part installation: If you over-tighten and crush a gasket, or if you don’t tighten bolts tight enough or in the correct sequence, those gaskets and bolts can leak oil.
- Oil filter “double gasket”: This is a common mistake that happens when replacing an oil filter. The old filter gasket sticks to the engine, and the new filter and gasket are installed on top of the old gasket. This often results in catastrophic engine oil loss.