Ever notice a puddle of oil under your car and wonder how to figure out where it is coming from, and what you can do to stop it? You can determine where the leak is originating so you can take steps to fix it.
Degrease the engine block--work around the valve covers, under the engine and around the oil pan to obtain a clear, clean view to determine the source of the leak. It is hard to find it when there is oil everywhere.
Drive the car or run the engine so the oil leak will start up again and show itself. If you are dealing with a very small leak, it may not appear right away and may even take a couple of days before you notice it. If the car is parked in the garage, lay out brown paper or cardboard overnight under the engine area and oil pan so that any leaks will be evident on the paper.
Check under the car to where the oil filter attaches to the engine block. Check the filter for tightness. If it is loose, further tighten it. In some cases, this will stop a leak, although you may have to change the gasket if it is worn and isn't creating a proper seal.
Check around the seams of the oil pan, where it bolts into the bottom of the engine. If you find leaking here, you may be able to get away with tightening the pan bolts further according to proper torque settings for your car, or you may have to remove the pan and replace the gasket. In other cases, the pan gasket may be fine, but a seal--for instance, at the front of the pan--may be the problem. Typically, when you replace the pan gasket, the seal will be sold right along with it. Both should be replaced at the same time.
Check the drain bolt on the oil pan. It may just be a bit loose and some tightening could be a quick fix. In some cases, the bolt is stripped--in which case, you would either have to rethread the pan to fit a new bolt or you may try to get a "fix-it" type bolt that is tapered and specifically designed to thread itself into the pan.
Check the oil pressure sending unit. These units will be found in various locations, depending on the make and year of the vehicle. Many times, they will leak. The unit will be attached to the engine block with a fitting. You may have to get a repair manual specific to your vehicle to locate yours. Sometimes the fitting is loose; other times, the unit may need to be replaced.
Look at the valve cover gasket area; this is a popular source for a leak. The gasket is between the valve cover and the engine block. The gaskets may be worn or cracked, allowing oil to leak through. The best way to check this area is to wipe clean the seam area where the gasket sits and also 2 to 3 inches below the gasket area on the engine block. Follow up after running the car to see if the area is still clean and dry. If you find a leak there, you may be able to re-tighten the hold-down bolts for the covers using a torque wrench according to proper torque for your specific car. If this doesn't stop the leak, you may have to remove the covers and replace the gaskets.
Check the head gasket area. This is where the engine heads sit onto the block. If you find a leak here, there is a chance that you are just experiencing what is called "blow back" due to a bad pcv or kinked pcv hose, which causes back up pressure. The repair of the hose or the replacement of the pcv may solve the problem. In other cases, new head gaskets may be needed, which is a larger job.
The better you degrease the engine and under the car, the easier it will be to locate the leak.
Whenever you are under the car, be sure it is properly supported and that you have safety glasses on so no oil or debris gets into your eyes. Make sure the engine and exhaust pipes are cool before probing around and searching for the leak or while cleaning the engine.