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.