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Pelican Technical Article:

Oil Leak Diagnosis

Nick Czerula


2 hours2 hrs







Applicable Models:

BMW Z4 Coupe/Conv (2006)

Parts Required:

Engine oil

Hot Tip:

Work with a cool engine

Performance Gain:

Repair oil leak

Complementary Modification:

Replace oil

The S54 performance engine used in BMW Z4M models is the big brother of the S50. With a bigger bore, more electronic technology and an advanced air and exhaust system. A one piece aluminum cylinder head construction keep weight down, while technology like adjustable camshaft angle and variable valve lift help to keep the engines efficient.

The crankshaft is sealed using rubber lipped oil seals. With rubber profile or sealing O-rings used on many of the parts. The oil filter stand is good example of a component utilizing a sealing O-ring.

The VANOS assembly is sealed a few different ways. There are O-rings for the pressure relief valve, a flat gasket sealing it to the cylinder head and a steel rubber mixed gasket used to seal the electronic controls for the VANOS actuators. All of which can leak.

Some trouble with molded rubber profile gaskets are these gaskets dry out over time, allowing engine oil to leak. For example, the valve cover gasket uses a molded rubber profile gasket, it leaks at the front and sides. Sometimes at the curve of the cylinder head cover, or at the lowest edge near the exhaust.

In this article, I'll go over how to pinpoint the source of an engine oil leak. Problem areas, components and tips on narrowing down the culprit are in the following text. With any leak, it helps to clean the area and monitor it for fresh oil.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability.

Vehicle models change and evolve as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Lift and support the front of your vehicle. See our tech article on jacking up your Z4.

This photo shows the top of an S54 engine.
Figure 1

This photo shows the top of an S54 engine. The trouble with an oil leak is it usually spreads all over the bottom of your vehicle, making it hard to determine where the source is. Start by following the oil, you will notice some of the oil on the engine is darker and dirtier, this is the oil furthest from the leak. Follow the oil toward the cleaner area, sometimes even spotless with just a coating of light colored oil. Look for leaks at the right side (yellow arrow) of the engine from below. Always suspect the valve cover and crankshaft seal as it can fling oil up and all over the side of the engine. At the front of the engine (red arrow) the problem would be the VANOS seals, crankshaft seal or the valve cover. If a leak at the left side of the engine seems to come from the top of the oil pan, check if the oil filter housing is the culprit.

This photo shows the right side of the engine with the splash shields removed.
Figure 2

This photo shows the right side of the engine with the splash shields removed. Note the wet area on the front of the oil pan (red arrow). If you were to follow this leak up, toward the VANOS unit you will be able to determine where the leak is coming from. If the oil is in fact coming from the VANOS unit or just below it, replace the seals for the VANOS unit. If the oil looks like it is coming from the crankshaft pulley, or spread out around it, the cause may be the crankshaft seal. When diagnosing a problem with the crankshaft seal, you are dealing with oil being flung around the side of the engine. Remove the drive belt and inspect the side of the engine. Look for oil starting low and lessening as it moves up. If you have oil residue on the A/C compressor or the engine mount bracket (yellow arrows) the valve cover is the most likely cause.

This photo gives a better view of the left side.
Figure 3

This photo gives a better view of the left side. Note the wet spot near the oil pan seam (yellow arrow). If the oil residue emanates from the seam only and not above, the oil pan is likely the issue. Keep an eye on the oil level sensor (purple arrow) these seem to be leaking on all S54 engines.

This photo shows the left side of the engine, note the oil surrounding the oil sensor (red arrow).
Figure 4

This photo shows the left side of the engine, note the oil surrounding the oil sensor (red arrow). In this case, the oil was coming from above. I followed it up and found the oil filter stand to be leaking. When dealing with leak on the left side of the engine, keep in mind the color of the oil. If it looks red, it could be a power steering fluid leak. Check the bottom of the reservoir for signs of leaking hoses, this is very common. Be sure you aren't chasing a coolant leak on this side as well, mixing with some dirt or residue made to look brown. There is a large coolant pipe set on the left side of the engine. If you suspect cooling system, pressure test the cooling system and look for active leaks in this area, see our tech article on cooling system pressure testing.

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Page last updated: Mon 1/22/2018 03:19:51 AM