Engine oil leaks should not be ignored. Oil leaks can leave greasy ugly stains on your driveway. But the real danger is potential engine damage or failure if your engine runs low on oil.
Oil leaking at the back of the engine may also cause the clutch to slip if your vehicle has a manual stick shift transmission. Oil can also produce blue smoke and unpleasant odors if it drips onto a hot exhaust manifold or exhaust pipe.
The first sign of trouble is usually drips or stains under your vehicle after it has been parked overnight. If the color of the liquid is dark brown or yellow, and it feels slippery or greasy, it is probably motor oil. A pink or red slippery liquid would most likely be automatic transmission fluid, while green or orange liquid with a sweet smell would most likely be antifreeze. A clear, oily liquid would probably be power steering fluid.
If you suspect an oil leak, check the oil level on the dipstick (engine off) to see if the oil level is low. If it is low, you probably have an oil leak. If the oil level is okay (between ADD and FULL marks on the dipstick), check the other fluid levels (ATF, coolant and power steering fluid) to see if any of those fluids are low.
Engine oil leaks occur most often at the valve cover and oil pan gaskets, timing chain cover and the front and rear crankshaft seals. As an engine ages, heat can cause cork gaskets to harden and shrink. Heat can also cause rubber (neoprene) gaskets and seals to harden and lose elasticity. After six or seven years of service, the engine may start to leak oil. The older the engine, the more likely it is to leak oil due to aging gaskets and seals.
Oil leaks can also occur if the crankcase is overfilled with too much oil, or the Positive Crankcase Ventilation (PCV) system is clogged, allowing pressure to build up inside the engine.
When oil leaks out of an engine, it attracts dirt. So look for greasy stains around or below gasket seams and seals. Sometimes you can see oil dripping out while the engine is idling. But more often than not, the oil just slowly seeps out causing a buildup of grease in the vicinity of the leak.
Crankcase oil additives can sometimes help slow a leak by causing aged gaskets and seals to swell, but no additive will stop a major leak or repair a broken gasket or worn seal. Sooner or later you will have to replace the leaky gasket or seal.
NOTE: Some motor oils are specially formulated for high mileage (over 75,000 miles) engines. These oils contain extra seal conditioners to help keep gaskets and seals soft and pliable so they don’t leak. Using this type of product in a high mileage engine can reduce the development of oil leaks.
To fix a leaky gasket, remove the cover or component over the gasket and scrape away all the old gasket debris from both mating surfaces. Wipe the surface clean with a rag. Then apply gasket sealer to both sides of the replacement gasket if it is cork (DO NOT use sealer on rubber gaskets), then position and reinstall the gasket on the cover. Then install the cover and tighten the bolts to specifications.
DO NOT overtighten pan cover bolts as this may crush and damage the new gasket. Some gaskets have built-in steel grommets that limit how far the gasket is compressed when the bolts are tightened down. When tightening bolts on a valve or pan cover, start with the center bolts and work towards the ends, tightening alternate bolts on either side to even out the loading on the gasket. Use an accurate torque wrench and follow the vehicle manufacturer’s torque recommendations. Check each bolt twice to make sure all are tight.
Valve cover gaskets are usually easy to replace, but intake manifold gaskets, pan gaskets and crankshaft seals are much more difficult. Some rear main seals require the removal of the transmission/transaxle and flywheel to be replaced.
To fix a leaky gasketless joint that is sealed with RTV silicone, remove the cover, scrape away all the old sealer and wipe both mating surfaces clean. For many of these applications, you can install an aftermarket gasket (if available). If no gasket is available, apply a fresh bead of RTV silicone sealer to reseal the joint. If using sealer, apply a one-eighth inch bead of silicone on one mating surface. Be sure to go around all bolt holes. Be careful not to smear the sealer during installation. Then replace the cover and tighten the bolts. Wait 30 minutes or so before starting the engine to give the silicone adequate time to cure.
On late model engines with oxygen sensors, use a low volatile type of silicone approved for use with oxygen sensors. Some silicones contain chemicals that can be drawn through the engine's PCV system and contaminate the oxygen sensor.
To replace a leaky seal on the front of the crankshaft, the crank pulley/harmonic balancer must be removed before the seal can be pried out. This requires a gear puller. DO NOT pound on the pulley/balancer because this may damage it. If the surface of the crankshaft is worn, a slip-on repair sleeve can be installed to restore the surface. A special seal is usually required with a repair sleeve.
Leaky rear main crankshaft oil seals are time consuming to replace because it involves dropping the oil pan and unbolting the rear main crankshaft support cap inside the engine. On applications that have a one-piece rear main oil seal instead of a split seal, the flywheel has to come off, which means pulling the transmission. This might be a better job for a professional to do.