How To Fix A Leaky Oil Filter Housing On An N51, N52, N54, Or N55 Engine

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If your oil filter housing is leaking on your N51, N52, N54, or N55 BMW engine, you need to take care of it ASAP, or it could lead to catastrophic failure. Here's how. 

Oil filter housing leaks are common on just about all BMW's. The gasket which seals the housing to the engine block or cylinder head degrades over time ultimately allowing for oil to leak out past the seal. It makes a massive mess which is a problem in itself, but the N5X family of engines has a unique problem that can arise from a simple oil filter housing leak: your engine can consume the serpentine belt through the front crank seal.

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Yes, you read that correctly. The reason this happens is pretty simple, actually. The design of the harmonic balancer/crank pulley assembly means the belt can only come off the crank pulley between the engine block and crank pulley itself as it's blocked from falling off the front by the harmonic balancer. The second issue is the crank pulley is very close to the engine block which allows for oil to drip onto the pulley and belt. If this happens it can cause the belt to slip off the pulley. If it slips off the pulley the belt will get wedged between the crank pulley and engine block, it will then get shredded, and then forced through the front crank seal. If this happens, the repair required to remove the shredded belt from inside the engine becomes astronomical compared to the cost just to replace the the leaking oil filter housing gasket.

With that said, if you see a leak around the oil filter housing it is worth it to do the repair to prevent a bigger problem later. All oil leaks are a problem, but an N51, N52, N54, or N55 engine, it can become catastrophic.

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Tools needed to complete this repair:
Parts needed:

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Step 1:

This is general advice for all vehicles with N51, N52, N54, and N55 engines. Remove the intake snorkle, air box, engine cooling fan, and anything else that is going to be in your way of being able to gain access to the fasteners securing the oil filter housing to the cylinder head. Most of these pieces are held in places with torx screws or expanding rivets. It is also going to vary by the specific model of vehicle you own. On some vehicles it may be necessary to remove the bracket for the power steering reservoir. It is secured by the alternator mounting bolts which are typically aluminum. So make sure you have spares if you see you have a bracket like this as the bolts are one time use only. Once the fan is out of the way I highly recommend removing the serpentine belt(s) and covering the pulleys with a towel before getting to the next steps.

N54 and N55 engines only:

It will be required to remove the intake manifold on the N54 and N55 engine in order to gain access to the rearward bolt securing the oil filter housing to the cylinder head. Removal is going to vary between the N54 and N55 engine but it is required in order to remove the oil filter housing as the rearward bolt is completely blocked by the intake manifold.

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Step 2:

First step in the process of removing the oil filter housing is to allow oil to drain back into the engine block out of the housing. I do this by opening the oil filler cap and removing the oil filter housing cap. Upon removal of the oil filter housing cap along with the filter (which will remain attached to the filter housing cap) a decent amount of oil will drain back into the engine block. There will be oil left in the housing so be prepared to extract it out using a syringe (I use CTA 7075 for this). Once a majority of the oil is removed from the housing I go one step further and use a few shop towels to seep up the remaining oil. I leave the shop towels in the housing to prevent anything from falling into the housing which may end up inside the engine. 

For BMW's with an oil cooler attached to the oil filter housing:

If your BMW has an oil cooler connected to the oil filter housing you will need to remove the coolant or oil lines attached to the housing. I recommend having a few towels handy as this could be a mess to a degree. I use hose pinch off pliers to prevent the mess from getting too big. Make sure the cooler lines are out of the way.

Step 3:

Next step is to remove the upper radiator hose from the oil filter housing. There is a metal clip which retains the coupling to the oil filter housing. I use a pick to pull this clip back and then wiggle the hose off the connection on the housing. There is an o-ring inside this coupling which seals the upper radiator hose coupling so it may take a few wiggles. I use hose pinch off pliers in an effort to reduce the mess. Coolant will spill out so make sure you have a towel below this area to try and soak up the coolant as much as possible and reduce the mess. From Step 1, you should still have the pulleys covered. Bend the radiator hose out of the way so it's not interfering with your work area.

Step 4:

Now you can start to remove the oil filter housing from the engine. Disconnect the oil pressure sensor first. If working on an N54 or N55 engine with the intake manifold removed you will have easy access to the rearward E10 bolt. If you have an N51 or N52 you will need to use a universal E10 torx socket with an extension to gain access to this bolt under the intake manifold. I recommend breaking this bolt free first before working on the others. Once all the bolts are loose you can use an 8mm ratcheting stubby wrench to remove the bolts the rest of the way. The 8mm stubby is especially useful for the bolt under the intake manifold. Once the bolts are removed you can completely remove the oil filter housing from the cylinder head.

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Step 5:

At this point I thoroughly clean the oil filter hosuing and remove all oil film and dirt that has accumulated. I recommend paying close attention to the engine as well as depending on the severity of the oil leak the front of the timing cover will be coated in oil and dirt. I recommend cleaning as much of this grit as possible. Also, the oil leak has a tendancy to leak in and around where the alternator bolts up. If you really want to go into it I recommend removing the alternator to gain more access to the engine block to thoroughly clean it up. If you do remove the alternator on an N51 or N52 engine make sure you have a replacement bolt set as the bolts are one time use only. Also make sure you clean the mating surface on the cylinder head and remove as much of the gasket material as possible. I use a scothbrite pad on the heavier stuff that I can't remove with a plastic scraper. Also use some brake parts cleaner on a clean shop towel to remove any and all oil film/debris.

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Step 6:

After cleaning up the mess from the leaking seal, install the new oil filter housing gasket. It can only go in one way. If the oil cooler gasket between the oil filter housing and oil cooler shows signs of a leak, take the time to replace it now. In my experience this gasket tends to not leak but if you have any doubts as to whether it is or not just replace it. Once the new gasket is in place install the oil filter housing back into location on the cylinder head. Start the bolts by hand to make sure they aren't cross threading. The lower bolt that faces the intake manifold should be fully tightened first as you will have the least amount of room to work with. I recommend alternating as you tighten the bolts down. Once the bolts are fully seated torque to spec (see bottom of post for exact spec). 

N54 and N55 engines only:

Reinstall the intake manifold with new intake manifold gaskets. This will be the reverse of removing it. Torque the manifold to the cylinder head to spec.

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Step 7:

Reinstall any hoses and replace any seals for the oil cooler hoses. For the rubber hoses and the o-ring for the upper radiator hose I use a tiny bit of silicone to aid in installation and to prevent any accidental damage from occurring upon reinstallation. Make sure all bolts and clamps are tight. Add oil to the oil filter housing before putting a new oil filter in. This will prevent a dry start. I usually put 2/10th's of a liter in to start with. With the oil filter kit you will install new o-rings but you will not use the crush washer (unless you're also changing the oil). Install the oil filter housing cap with filter and torque to spec. Add some coolant to the expansion tank mixed to 50/50 (or 60/40 in a cold environment) until at the max allowed level (indicated on expansion tank). 

Step 8:

Reinstall the belt, fan, and air intake at this time. At this point you will have a fully assembled engine bay. Once this is complete start the engine and let it run for a few minutes. Check for any oil or coolant leaks. You may notice some smoking on startup but this will occur if you use any type of cleaner such as brake parts cleaner to clean up the oil leak. It should dissipate quickly. Once you have determined there is no leak follow your vehicles cooling system bleed procedure. On any N5X engine you can use the self-bleeding function which will turn on the electric water pump. The cooling system bleed procedure is slightly different as it's a "self-bleeding system". In order to start the self-bleeding procedure you will need a battery charger to maintain battery voltage during the function as this process will take 12 minutes to complete. Follow the steps below to use the self-bleed feature:

  • Switch the ignition on but do not start the car.
  • Set heater to maximum temperature and turn blower speed to lowest setting.
  • Press accelerator pedal for 10 seconds to the floor (the engine must not be started). 
  • The bleeding procedure will start after 10 seconds. To confirm you should be able to hear the electric water pump.
  • After 12 minutes the water pump will turn off and the bleeding procedure is complete. Top up reservoir if low.

Key torque specs for reassembly:

  • Oil filter housing to cylinder head - 22Nm
  • Oil filter housing cap - 25Nm
  • Oil cooler to oil filter housing - 16Nm
  • Intake manifold to cylinder head (N54 and N55 engines) - 15Nm

If you have any questions, leave them in the comments below and we'd be happy to answer them.  

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