BMW E90 328i Valve Cover Oil Leak: How to Diagnose It

Oil around the top of a 2007 to 2011 BMW 328i engine usually points to the valve cover, but not always. The cover gasket, the Valvetronic motor seal, the spark plug tube seals and the breather hose all sit in the same area. This guide helps you work out which one is leaking before you buy parts, and covers what the repair involves. Factory facts come from BMW's repair instructions and torque tables for the E90 328i, which list the engine as N52K, with a link to the page we read.

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Models and engine variants covered

This guide is for the E90 328i sedan. In the US, FCP Euro lists the 328i from 2007 to 2013 under the N51 and N52N valve cover procedure, and BMW's manual for the E90 328i covers the earlier N52K. There are 3 cover designs to know:

FCP Euro describes early N52 engines as having a magnesium cover with an external crankcase vent valve. We could not tie the switch to a production date from a factory source, so identify your engine by looking at the cover. Check your VIN with a BMW parts catalog before ordering anything.

Recognizing a possible upper-engine oil leak

FCP Euro lists these signs of a failing valve cover gasket on the N51 and N52N:

• Low oil level or frequent top-ups.
• A burning oil smell when the engine heats up.
• An oily or greasy engine compartment, most visible around the back of the cover.
• Rough running or misfires, when oil gets into the spark plug wells and interferes with the spark.

Source: FCP Euro N51/N52N valve cover guide. FCP also says to deal with it early, because ignoring it can lead to costly damage.

Narrowing down the leak source

Oil runs downhill, so a wet lower engine does not prove the leak is low. Clean the top of the engine with brake cleaner, drive for a few days, then look at the cover first. Work from the top down:

• Cover edge: oil along the perimeter, especially at the back, points to the cover gasket.
• Spark plug wells: oil in the wells points to the spark plug tube seals, which FCP Euro says are replaced along with the gasket.
• Valvetronic motor: FCP Euro says a faulty Valvetronic motor seal makes oil pool in the center cavity of the cover. Check around the motor and the sensor seal at the front.
• Breather hose: the hose on the back of the cover can be fragile with age, per FCP Euro. Look for a wet or cracked hose before blaming the gasket.

Checking the cover and adjacent seals

BMW's N52K procedure tells you to replace the gaskets and the slotted sleeves that guide the ignition coils in the cover, and to clean the sealing faces without metal-cutting tools. It also calls for new aluminium screws on the magnesium-crankcase engine. FCP Euro adds that the metal spark plug sleeves on the N51 and N52N are one-use and have to come out to remove the cover.

Before you order, inspect the cover itself for cracks and the sealing face for damage. BMW's instructions we read give no distortion limits, so this is our advice rather than a factory spec.

Choosing the correct repair scope and parts

• Gasket only: fits a clean cover with no cracks or damaged sealing face. Replace the plug tube seals at the same time.
• Cover replacement: if the cover is cracked or the sealing face is damaged. On an N52K, buy new aluminium screws either way.
• Valvetronic seals: FCP Euro says the motor gasket and sensor seal are replaced after the cover is installed, which is easier and protects the sensor seal.

FCP Euro's N51 and N52N guide lists its gasket under BMW number 11127582245. Confirm fitment against your VIN, since the engines differ.

Repair planning and safety questions

Torque values for the cover are small, so use a torque wrench that reads in the low range.

Job outline from BMW's N52K procedure (11 12 000):

1. Remove the ignition coils, release the ignition wiring harness in the cover area and remove the tension strut.
2. Unlock and detach the vent hose. Pull off the metal bracket if needed.
3. Release the screws on the electric servomotor, including the one under it, and remove the motor. BMW refers to TIS 11 37 3AZ for those torque values, so look that up for your car.
4. Release the secondary air valve nuts if needed (BMW refers to 11 72 1AZ).
5. Release the cover screws. BMW notes the screws have different lengths and are placed by bushing shape, so keep track of where each one came from.
6. Clean all sealing faces, replace the gaskets and the slotted coil guide sleeves, and install with new aluminium screws at 9 Nm.

Safety notes: let the engine cool first. FCP Euro suggests disconnecting the battery ground before moving harnesses, and being careful not to drop sockets into the engine bay. FCP Euro took about 5 hours on an E92 N51 the first time it did the job, and quoted $600 to $1,000 at a shop in 2020, so treat the cost as a rough, dated figure.

Parts and tools

• N52 valve cover gasket set (check it matches your cover type)
• External Torx socket set (E8 and E10, per FCP Euro)
• Low-range torque wrench
• Universal joint and extension set

Post-repair inspection and follow-up

• Before closing it up, check that the gasket is seated all the way around. FCP Euro warns it can roll or shift when the cover goes in.
• Reconnect the breather hose carefully, and the electrical connectors and ground straps you moved.
• After reconnecting the battery, FCP Euro says the Valvetronic system may need a reset. With ISTA or INPA you can do it directly, or turn the ignition to accessory mode a few times. It says rough idle can last a couple of days.
• Check the oil level, then recheck the cover edge, plug wells and Valvetronic motor for fresh oil after a few drives.

For other E9x fasteners, see our E90, E91, E92 and E93 torque specifications.