When you see a dark patch under the car on your nice white concrete driveway, this is caused by Oil Leaking out where it is not supposed to.
Cars up until the 90's always used to leak some form of oil. When you visited a New Car dealership they would have a tray under the engine to catch oil so it did not mess up their floor. Now we expect not to see that.
The oil leak can come from several places in a car:
- Oil Pan Gasket - This gasket wears out frequently. Oil Pan is at the bottom of the engine
- Oil Pan Drain Plug - Every time the oil is changed in the engine the Drain Plug is removed and then put back. If the drain plug is not put back tightly enough or cleaned prior to being put back, then oil can seep out of it. The drain plug is located on one of the sides of the oil pan.
- Oil Filter - It can happen sometimes that when you get your oil filter changed that it is not put back on correctly leading to an oil leak.
- Valve Cover - Seal to the Valve Covers need to be replaced regularly. Depending on your engine you may have multiple Valve Cover Seals to replace. Valve Covers are are at the Top of the Engine.
- Crankshaft Seals - As engines age these seals will wear out. One is at the side of the engine with the belts on it and the other is hidden by the transmission.
- Timing Chain Cover - If your car has a Timing Chain, it will be lubricated by oil and the Cover that protects it has a Gasket to stop oil leaking out. Over time the Timing Chain Cover Gasket will need to be replaced.
- If the car is rear wheel drive then it will have an axle with a differential. This differential has oil in it and this can leak out.
- Stick Shift (Manual Transmission) can leak oil like an engine. In this case the oil patch will appear under the transmission (gearbox).
For difficult to find Oil Leaks in Cars, Mechanics add a dye to the oil that shows up under a UV light. The dye is added and the engine run. Then after a while, the engine is turned off and the mechanic shines the special UV light onto the engine. This UV light makes the Dye show up and the Mechanic can trace the oil leak back to source. UV Light Kits and Dye are available from Auto Parts stores.
Read about Engine Oil Leaks