Common Causes of Oil Leaks

Motor oil leaking from the vehicle.

While it can be very easy, and sometimes tempting, to ignore the signs of oil leaks in your vehicle, it is never a good idea to go too long before inspecting the cause of the leak and repairing it. Motor oil is responsible for protecting and prolonging the life of your engine, and is one of the most common fluids to check and refill as necessary. Ignoring oil leaks, no matter how big or small, can potentially lead to engine damage. Whether you notice a puddle of oil underneath your vehicle after it’s been parked or a few drops leaking while it’s running, oil leaks of all sizes should be inspected and repaired, and oil levels refilled, as soon as possible to prevent more expensive engine damage. Read on to learn about the most common causes of oil leaks in your vehicle.
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Loose or Damaged Drain Plug

Puddle of motor oil on a garage floor.

If you’ve ever changed the oil in your vehicle, you’ve loosened and removed the drain plug. The oil drain plug on your vehicle is responsible for keeping oil from escaping or leaking out of the oil pan, which is the reservoir that collects oil that has been pumped throughout the engine. Oil that is collected in the oil pan is pulled back into circulation by the oil pump and is filtered before cycling through the engine again. The oil pan and drain plug are located on the bottom of the engine directly beneath the crankcase or block. Due to its location, a loose drain plug or damaged drain plug seal will produce prominent oil leaks, likely leaking in drops or leaving puddles of dark oil underneath the vehicle. Some drain plugs are installed with a drain plug seal, and these seals often need to be replaced at every oil change. The drain plug seal can wear out over time, especially if it is not regularly replaced, and this is a common cause of oil leaks. In other cases, failing to completely tighten the drain plug, cross-threading the drain plug, or damage to the oil pan or plug can also cause oil to leak. If you notice oil streaks near the engine oil pan or puddles underneath the vehicle, or if you experience a significant drop in oil levels, you might have a damaged or loose drain plug, seal, or oil pan. Repairing or replacing your oil drain plug or drain plug gasket is a simple task with the right parts to get the job done from O’Reilly Auto Parts.
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Worn Oil Filter Seal or Oil Filter Cap

Oil filters and filter caps keep the oil in your vehicle clean and contaminant-free to maintain your engine's performance and protection. While the oil filter strains and removes contaminants from the oil before it reaches the rest of your engine, the oil filter cap ensures the filter cartridge is sealed securely to retain the motor oil and prevent leaks. Your oil filter maintenance may look different depending on the type of oil filter your vehicle uses. Screw-on filters have a rubber seal pressed against the engine block, while canister oil filters are sealed by a cap with an O-ring. The O-ring on the cap should be replaced any time it is removed, and the O-ring on the filter should be lubricated with fresh oil during the installation process to prevent tearing. After removing a spin-on oil filter, make sure the seal is not still stuck to the engine, as this can cause rapid oil leaks. Oil filters and oil filter caps work together to lubricate and protect your engine. However, oil filters and filter cap seals can degrade over time if they are not replaced regularly, allowing oil to leak through the filter and escape from the cartridge. Filter leaks can also occur if the filter is loose, displaced, clogged, not installed securely in the filter housing, or if the cap is cracked or cross-threaded. If you notice an illuminated engine oil light, reduced engine oil levels, or see oil leaking or dripping from the oil filter housing, you likely need to replace or repair your oil filter or cap. To avoid leaking oil filters, follow the instructions and intervals listed in your owners manual to stay current on oil and oil filter changes.

Worn or Damaged Engine Gaskets and Seals

There are numerous engine seals and gaskets that are each responsible for preventing fluid from leaking from specific areas of the engine and reducing the risk of harmful contaminants reaching the oil supply. One of the most common signs of a worn, damaged, or loose seal or gasket is oil leaks. Seals and gaskets can experience wear over time, or may break down due to excessive friction or heat, resulting in oil leaks. If the engine is not properly lubricated or is experiencing abnormally high oil or vapor pressure, seals and gaskets can crack or tear, dry out, or separate. Depending on where the seal or gasket is located, you may notice a few different oil leak symptoms, such as oil on the underside of the vehicle, the smell of burning oil, oil dripping from the front or rear of your engine, or reduced oil levels. Locating seal or gasket oil leaks can be tricky if you’re not sure where to start looking. Listed below are a few of the most common engine seals and gaskets susceptible to oil leaks:


Camshaft Seal

If oil is leaking from your camshaft seal, immediate attention is often required. This specific oil leak puts your engine in danger of timing belt damage, which could result in bent valves, cylinder head damage, or other permanent engine damage.

Crankshaft Seal

A leaking crankshaft seal or front shaft seal can cause oil leaks near your harmonic balancer or crankshaft pulley. The crankshaft seal can allow oil that seeps around the balancer or pulley to be tossed all around the engine compartment and can cause belt damage or slippage. If the crankshaft seal begins to fail, the oil may leak from the underside or front of the engine.

Rear Main Seal

The most common cause of rear main shaft seal oil leaks is wear and tear due to low oil levels, extensive use, and age. Vehicles that sit for long periods of time without being started or running may have an increased risk of rear main seal failure. These conditions can cause drying, hardening, cracking, shrinking, and tearing of the seal. A worn and leaking rear main seal can cause oil leaks between the engine and transmission that could result in starter contamination and failure. Rear main seals often also leak rapidly, which can pose a serious threat to the health and overall performance of your engine if not monitored closely or repaired.

Valve Cover Gasket

The easiest way to recognize a leaking valve cover gasket is an oil-covered valve cover or a strong smell of burning oil when the engine is running. Oil that leaks from the valve cover often lands on the exhaust manifold, which is among the hottest parts of a running engine. In some cases, you might experience smoke coming from the engine as the leaking oil burns off, and this could start a fire in extreme cases. A valve cover leak should be tended to promptly and properly to ensure you can continue to drive safely and minimize oil loss.

Cylinder Head Gasket

Due to constant exposure to high internal engine pressure and temperatures, vibrations, and hot coolant and oil, it’s not uncommon for cylinder head gaskets to break down over time. Head gaskets can also fail rapidly due to low coolant levels or engine overheating, which may allow oil to drip from around the cylinder head. This also commonly causes coolant and oil to mix or coolant to enter the cylinder and burn, which can produce white smoke or oil that looks milky or frothy. A damaged head gasket should be replaced promptly to prevent contaminated oil or low coolant levels from causing complete engine failure. You can learn more about head gasket failure with our helpful article.

Timing Cover Gasket

If you notice oil leaking from the sides or edges of your timing cover, you likely have a damaged timing cover gasket. These gaskets can crack over time or due to damage from high internal engine pressure, potentially allowing dirt and debris to enter critical areas of the engine and damage the timing belt or chain, gears, and other components. Timing cover leaks should be inspected and repaired, and the urgency of the repair depends on the amount of oil leaking from the timing cover.

Oil Pan Gasket/Seal

Most oil pan gaskets or seals are rubber or silicone in composition, and can degrade over time. Age, heat, and constant exposure to oil vapor pressure can all contribute to the wear and tear of oil pan gaskets and seals. Oil pan gasket leaks can sometimes result in oil dripping on the exhaust manifold, producing smoke as the oil burns. These are typically slow oil leaks that don’t pose an immediate threat to your vehicle. However, if you don’t replace the gasket, you will likely need to monitor your oil level closely and refill as necessary to ensure your engine is lubricated properly.

Loose Oil Filler Cap

When you refill or top off your engine oil level, you have to loosen and remove the oil filler cap. The oil filler cap is located on the engine near the top or the side and may be installed in one of the valve covers. This cap seals the oil opening to prevent oil from spilling out of the opening neck, contaminants from entering the oil supply, and oil vapors from escaping. In order to do its job properly, the oil filler cap must be fastened and sealed securely. If your oil filler cap is loose or has a damaged seal, it can no longer protect your oil against contamination. If you smell burning oil while driving your vehicle, or if there is noticeable debris in your oil, you could have a loose or missing oil filler cap. Tightening the cap is a simple fix, but in some cases, it may be necessary to replace the oil filler cap or seal to complete your repair. If you need a replacement oil filler cap, O’Reilly Auto Parts carries a variety of replacement caps for most vehicles.

Cracked Oil Pressure Sensor

Oil pressure sensors monitor oil pressure while the engine is running to alert drivers to potential oil supply issues, either by feeding an oil pressure gauge or activating a warning light if oil pressure levels drop below a set threshold. Oil pressure sensors are usually located in the engine block close to the oil filter and are in direct contact with the oil supply. If the oil pressure sensor cracks or breaks, oil leaks can occur. If you’re experiencing inaccurate oil readings, illuminated oil pressure lights, or oil leaking from near the oil filter or sensor, you may need to replace your oil pressure sensor or sensor unit.

Damaged Oil Pan

Draining motor oil from the oil pan.

The oil pan is the engine oil reservoir located underneath the block or crankcase. Oil is stored in the oil pan before being recycled and pumped back through the oil filter and throughout the engine. Due to its location, the oil pan is often exposed to harsh terrain and climate conditions, road debris, and contaminants, and can be damaged or become corroded over time. In extreme cases of damage, especially in an accident or if the vehicle bottoms out, the oil pan may crack and begin leaking oil. These cracks and dents can also damage the seal around the drain plug and cause leaks. Drain plug and oil pan leaks are often rapid, and this can cause dangerously low oil levels even on short drives. If your engine oil level drops suddenly, your oil level or pressure indicator is illuminated, you see puddles of oil underneath your car, or if your engine begins to tick or make metallic noises, you may have a damaged and leaking oil pan. Checking the oil level and condition, as well as inspecting the condition of the oil pan and its gasket, can help you determine the source of the issue.
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Too Much Oil

Regularly changing your car's oil is one of the most common and important tasks required to keep your vehicle running properly. It’s important to refer to your owners manual when refilling or changing your oil to make sure you are putting the right amount of oil in your car. Too much oil can actually harm your engine components. Overfilling your engine with oil can create increased pressure inside the crankcase that will attempt to escape through a number of seals and gaskets. These gaskets and seals can crack or blow out under pressure, resulting in oil leaks. If you notice oil leaking from any of your seals or gaskets, smell burning oil, see smoke coming from the engine, or hear strange noises from under the hood, you might have too much oil pressure and should check your oil levels using the dipstick. When it’s time to refill your motor oil or service any other fluid in your vehicle, we recommend following the specific fluid recommendations and instructions in your vehicle’s owners manual to prevent overfilling.

The Importance of Checking Your Motor Oil

Checking oil levels with the engine oil dipstick.

This article showcases some of the most common causes of motor oil leaks in your vehicle and is a great example of why checking, changing, and refilling your oil as specified in your owners manual is such an important part of maintaining and owning a car. Oil is designed to support and protect your engine’s health and performance, and one of the best ways to prevent oil leaks is to stay on top of your vehicle's oil condition and level. For helpful tips and information about choosing the right motor oil for your vehicle, understanding engine oil weights, the consequences of putting off oil changes, engine sludge formation, and details about synthetic oil, visit the O’Reilly How-To-Hub to find answers to any motor oil questions you may have. If you’re experiencing an oil leak and need to find the parts to make your repair, our Professional Parts People® can help you get the job done right.
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