Saturday, 27 July 2013

BMW 3 series 318i e46 n42 Sump Gasket Replacement DIY

My N42 engine, like every other N42 engine has so far leaked from all the known trouble spots and the sump gasket was no exception. It wasn't serious enough to be leaving oil on the ground, but I found I was getting quite a lot of clutch judder when the car had been left standing for a while and I was concerned that the oil was leaking backwards on to the clutch.

There don't seem to be many DIY's around for this job as people seem to be put off by the prospect of lowering the sub-frame  I've done a few big jobs on various vehicles so I felt up for the challenge, but I did arrange for a friend to help me just in case it turned out to be a real pig.

However, on my car I didn't find it to be too difficult at all and with an extra pair hands we had the job done in one Saturday. Due to the lack of DIY's I thought I would write one up as it may help somebody else do theirs.

I followed the procedure detailed in the Haynes manual, although I found it to be incorrect in a number of places. For starters it says you need to drop the anti-roll bar and the lower auxiliary belt pulley.  This is odd because Haynes tells you to maneuver the sump out towards the rear of the car and we couldn't see how either of those items were obstructing it! I did drop the ARB anyway as I had bought new bushes for it, but I am not convinced it was necessary.

Haynes says you need to replace the reinforcement plate bolts, the sub-frame bolts and the engine mounting nuts.  When I spoke to BMW they said this is not the case, they said that there is nothing special about any of those bolts and they don't replace them.  I did buy the full twenty sump bolts as they have a dry thread locking compound on them and considering the effort required to get to the sump I thought I would err on the side of caution. I also bought a replacement rubber O-ring for the bottom of the dipstick tube, this turned out to be a good call!

This guide mostly follows the Haynes manual, so if I have missed anything it will probably be in there! I am assuming you have drained all your oil before you have started this job!!! :)

There are some photos missing, I plan adding a few extra soon when I jack her up to see if she is now oil-tight! :)

Start by jacking up the car and supporting it on axle stands.

Next, remove the large piece of air-intake that also exists to try and make things prettier.

Next, you want to get the air-box out of the way, start by removing these two bolts.

The air-box is also held in place by a Jubilee clip on the air-hose and a rubber grommet thing on a plastic box beneath it, both circled in this pic.  Once the bolts are out and the Jubilee clip is undone, you should be able to just pull it apart from the other plastic box.

Next, remove the engine under-tray   This is held in place mostly be screws, but at the front it is held in place by some awkward plastic pop rivet thingies.  You need to negotiate the middle part out and then it will be loose enough to remove the whole thing!

Next the lower re-reinforcement plate needs to come out (I believe that on older cars this is some sort of cross brace rather than a plate).  There are eight bolts that are probably quite stiff, but nothing a drop of WD40 and a breaker bar couldn't handle.

The reinforcement plate off the car.

Before you go any further, now is the time to set up your support beam and make sure it is secure.

I had a question about how the beam attaches, so I've added the following photos which are hopefully helpful. My beam had two feet, one at each end which were braced against the edges of the engine bay... At the front of the engine a bit of metal sticks out with a hole in it, this is where you hook in the chain...

The feet of the beam.

The hook for the chain.

Next, we the undid the two nuts on each anti-roll bar collar and dropped it down.  We couldn't really see why this was necessary and wouldn't have bothered at all if I hadn't have already bought some replacement poly-bushes to do while we were there. :)

Haynes also talks about removing the lower auxiliary drive-belt pulley, but we couldn't see why this need removing either so we left in place. (A good thing really as the bolts looked very rusty!)

Next, was the steering rack pinch bolt, this was an E10 spline bolt that was fairly easy to shift.  However, to get at it the steering had to turned. Once the bolt was removed, we turned the steering back and engaged the steering lock before removing the steering UJ, this is easy enough, just requires some pulling and wiggling.

Next, remove the bolts holding the wishbone bush 'lollipops' to the chassis.

Next, we removed the engine mount nuts. (Viewed here through one of the holes in the wishbone) Double check the engine support is ok.

Next, we supported the sub-frame on a jack and removed the sub-frame bolts. There are two on each side, they were relatively stiff, but again nothing a breaker bar couldn't deal with! ;)

You can now slowly lower the sub-frame until you have good access to the sump.  Haynes says to be careful not put any strain on the power steering hoses.  That's true, but in reality we found that the hoses were quite long and we had ample room without being close to straining them.

One last component to undo:

This is a push-fit plastic breather hose (goes back to the crankcase breather valve) which attaches to the oil dipstick tube. Mine didn't want to play ball and was a little awkward to get off. I think I managed it with a screwdriver by inserting it inside the collar and pushing/wiggling something.

You might not have any trouble with yours, but if yours is stubborn like mine, here is a pic that proves it does come off!

Next we had to unbolt the oil dipstick at the top of the engine and then wiggle it out (we did try without removing it, but found the sump just got stuck.

Next, we undid the twenty bolts holding the sump in place and maneuvered it out towards the back of the vehicle.

Sadly, this is the only shot I took of the sump removed, but plenty of the engine internals!

There is a small rubber o-ring that sits at the end of the dipstick tube, I bought a new one of these and I was glad I did because the old one was incredibly brittle. The old one was stuck to the sump, however I fitted the new one to the end of the tube to try to ensure it didn't fall in to the sump (you'll see what I mean).

We cleaned it up, fitted the new gasket and then maneuvered it back in to position.  You need to guide the dipstick into the sump when maneuvering the sump into position. We found it impossible to get the dipstick in once the sump was bolted in!

Refitting as they say is a reversal of the removal.


  1. Was it successful? Thanks for this blog. I am about to embark on the same job.

  2. Not 100% sure, I haven't jacked it up yet for a thorough investigation, a new baby is slowing me down a bit! :)

    I hope to check it in a couple of weeks... having said that, what I can see of the sump looks dry, whereas before it was covered in oil, so I think it is promising!

    Let me know how you get on...

  3. Jacked it up today to check it over, and I can confirm the job was a success! :)

  4. thanks for the relationship! helped me a lot! Can I copy the images and do the instructions on the Polish forum? Greetings from Polish!

    1. Hi there,

      Of course you can, that would be great! As long as you put a link back to this blog... :)

  5. Excellent write up, many thanks. Just a few quick questions for you. When you use the engine support beam where do you attach the support on the engine and where do the ends of the beam bear down? Do you have any photos of these points. Also, the Haynes manual suggests that the car needs to be checked for alignment after the sub frame is removed and reinstalled; Is this really necessary, because this would be expensive at the stealership as they need to do it with the usual "specialist" equipment? Did you use sealant with the gasket? Any advice welcome. Many thanks, Mark.

  6. Thanks, I've added a couple of photos that hopefully make it clearer what to do with the beam, it is quite straightforward when you come to do it.

    I didn't use any sealant with the gasket, the mating surfaces of the sump were in good condition and the original lasted 90kish so I couldnt see any reason why the new one wouldn't.

    In my experience Haynes tends to be a bit over-cautious when it comes to alignment, I couldn't see why it would need it if everything went back as it came off, and I didn't notice any problems with the steering and suspension after... Of course your experience might be different, but if it were me I would just put it back together and see how it drives... If you do want it aligned I wouldn't take it to a stealership... There are plenty of independant garages that can do a full four wheel alignment...

    Hope that helps, and good luck! :)

  7. Many thanks for the quick update Ben, much appreciated. Ref the alignment, it's just that I had an E36 before and that needed an alignment after an accident, and the indy said I needed to take it into BMW because they weight the car up "with specialist weights" before they align the wheels with "specialist lasers", or something like that; no doubt to justify bending you over the counter and emptying your wallet with "specialist" fingers ha ha..Best regards, Mark

  8. Hi there Ben,

    I was just curious to know, did this actually fix your clutch juddering issues?
    My partner has the same model & has some serious judder problems. I am thinking the clutch is actually toast but this may be worth looking into as her sump leaks too.


  9. Hi there mate,

    Great work, tonnes of helpful info here. I'm ordering all of the bits and making a start when I get a couple of days off work to do it. Just wanted to say thanks for the detailed images, the annotations and the Haynes experience vs real world experience. I feel a million times more confident in doing this and will not be taking my car to a garage!