[Jazzbass]

Over the last few weeks I’ve been working on the E46 a lot, and I think someone got a little jealous the attention I was giving it:



The E90 decided it has had enough being ignored and popped up with not one, not two but three completely separate and unrelated problems. Yea for owning old BMWs!

OK, maybe that’s a bit unfair. The first problem is not a BMW at all. I was getting low tire pressure warnings about once every two weeks. Slow leak? Nail? Turns out it was a shitty plug job. One of the rear tires had been plugged (not patched). The left rear tire had worn down to about 3/32 and was now affecting the plug. This was the easiest yet most expensive problem to fix – buy new tire, get it mounted, done.

Problem two: Intermittent burning oil smell

This one surprised me. So about two months ago, right after an oil change, I started getting this intermittent burning oil smell. It would start about 2 minutes after I started driving, burn for about 2-3 minutes, and then go away. Did this almost every trip. So, to the Google and e90post. The two most popular suggestions were:

1. I spilled oil under the plastic engine cover when you did the oil change and it’s dripping down when you drive. Hahaha… no. First, I don’t spill oil and not clean it up. Second, it’s done this for a couple months. To spill that much oil I would have had no have put any in the actual engine. And I think I would notice if the engine had no oil.

2. The valve cover bolts broke and the valve cover is leaking oil. Now this is more reasonable because my car (2006 330i) has the then-new N52 engine. This engine has a magnesium-aluminum head and block, so BMW decided to use special aluminum bolts to hold shit together (word is that steel bolts had the wrong thermal coefficient of expansion. Plus steel + magnesium = white powder). Internet lore is that BMW screwed up torquing these very small aluminum bolts (the torque spec is 7 Nm + 90 degrees) and as a result they like to break. Two problems with this theory as well – first, I just had this problem a couple years ago. Three of my valve cover bolts broke and I replaced them all along with a new valve cover. And I torqued them correctly – even spent $150 on a new low torque wrench to do so. Second is that when the bolts DID break, I smelled oil constantly – nothing intermittent. So I doubted this was the reason.

Looking around, the engine was covered in oil, especially on the front. Underneath there was a good bit of oil, too, especially in the front right corner above the water pump:



Now there was one more suggestion from e90post that I laughed at first time I read it – the oil filter housing gasket was leaking. For reference, here’s the engine compartment of the E90. The oil filter console is front left of the engine (red arrow). The oil smell was due to oil dripping down onto the cats over in the right rear of the engine by the #6 cylinder (blue arrow). Oil filter housing gasket? Yeah right.



Actually, looking around, there IS a lot of oil around the oil filter housing. And on the back of it, too, under the manifold. And all along the front of the engine. Well, whether or not the oil filter housing gasket is the reason for the oil smell, I do have to admit that the damn thing does appear to be leaking. OK, let’s fix it. A quick search showed several DIYs for this, so I won’t recap everything in detail, but I will say that compared to doing this same job on an E46, changing this gasket on an E90 is 100x easier. Reason is that the oil filter console on the E46 is a big and a major support structure for engine accessories. The alternator, vanos oil lines, and power steering pump are all bolts to it. In the E90 the only thing you have to deal with is the upper coolant hose. That said, there are a couple things you can do to make this job easier.

First, remove the radiator fan, coolant hose and drive belts. These should take you about 10 mins to remove and free up so much room to work. The second thing to do is buy one of these:



This is a 1/4” drive E10 swivel socket. Only place you can get one in the US that I could find is Snap-On, so you have to pay Snap-On prices for this. This cost me $41. It is 100% worth it. The oil filter console is held on by three bolts, and without the E10 swivel you cannot get to this bolt:



without removing the intake manifold. And f**k that. Now, if you think like me you say to yourself “bullshit – you can get E10 swivel sockets for less than $41”. This is true, you can. In fact, I got a whole set a while ago (E4 – E18) for about $40. Problem is the E10 in all these sets is 3/8” drive, and it just doesn’t fit. The angle of that rear bolt and the location of the intake manifold mean there is almost no room to get a socket on it. The 3/8” drive swivel is too big and doesn’t fit. A regular 1/4" drive E10 socket with a standard universal joint doesn’t work. Nothing works except that damn $41 Snap-On socket. Believe me, I tried. Anyway, with the magic socket I was able to get the console off in about 10 mins:



Yep, this gasket is toast. Interestingly, the coolant section of the gasket (lower right in this picture) looks worse than the oil sections. But I didn't see any coolant leaks from here - just oil.



Clean, clean clean and everything's so pretty:





Bolt back together, torque, and done. Having done so many repairs on this car where I have to replace aluminum bolts, I bought a new set of bolts for this job as well. Turns out they were unnecessary – the three bolts that hold the console on are steel, not aluminum. Go figure – I thought steel + al/mg was bad, but apparently not always.



After I got the car running again I took it for a 30 mile test drive - no oil smell. That gasket was apparently the problem. I suspect the 2 minute delay was the time it took for leaking oil to run out of the console, down the front edge of the engine along the head/block seam, and then run down the right side of the engine from the #1 cylinder to the #6 cylinder, where it dripped down on to the cat, causing the burning smell. Why it stopped after a couple minutes I have no idea. Maybe the gasket only leaks when it's cold? So it'll leak on initial start up, and then when engine came up to temp everything expanded enough to stop the leak? Yeah, I know I'm grasping here.

Oh, and since I had the radiator hoses off, I decided to replace the accessory belt and tensioner. 80k miles on the car and all that. $100, 10 minutes, and done.

[Jazzbass]

Problem three: Losing coolant.

So the low light comes on. Sure enough, had to add a liter of coolant to get it back up to full. Hmmm… I don’t see any coolant puddles on the drive way, don’t smell any burning. Must be a slow leak somewhere but I don’t see anything. Internet research suggested a hairline crack in the expansion tank, but that info was a bit dubious. BMW seems to have figured out the expansion tank think in the E90, and I didn’t see any evidence of leaked/evaporated coolant around the tank. Well, because of the oil leak, I had to pull the engine tray and look around. And look what I found:



The good news - there’s the coolant leak. The bad news – that’s on the $120 hard pipe that goes from the water pump to the block:



80% of that coolant line is a steel pipe, but the end has a 6” length of rubber hose crimped on. This rubber part clamps to the outlet of the water pump. It’s this rubber part that’s leaking. Well, I’m in there replacing the oil filter gasket, might as well replace this too. Order the new pipe and bolt it in. It was surprisingly not difficult – you can see the exhaust manifold right next to the water pipe in the picture about, so I thought this was going to be a nightmare. On post I say on bimmerforums was a guy talking about replacing this pipe on his 530i, and he said it couldn’t be done without removing the exhaust. Well, if that’s true then I guess I need to get used to topping up the coolant every 6 months, because NFW I’m pulling the exhaust.

Well, turns out there was no interference at all. I removed the expansion tank and had plenty of room to work. Unbolting the rubber end from the water pump meant unbolting the water pump, but with the radiator out and the power steering lines out of the way, that was pretty easy. I thought I might have to do this, so I made sure I bought a new set of one-use-only Al water pump bolts just in case.



Removing the pipe from the block was pretty easy with a little leverage. The bolts that hold the pipe into the block are surprisingly small – M5 aluminum bolts maybe 10mm long. Again I got new bolts for these too, but damn if I could find a torque spec on these. So I just tightened them down as much as a dared and checked them after several drives. They seem to be holding, so that’s good.

So why the leak? Well, here’s my theory – the outlet flange on the water pump is ribbed. The rubber part took set onto these ribs when bolted to the original pump (see pic of old hose below). Then, when I replaced the pump a couple years ago, the rubber part never quite meshed correctly with the new pump. Wasn’t enough to leak a lot, but just enough mismatch to weep a bit. Weeping over the course of a year and the coolant level is now too low.

[86911TLCAB]

Have a similar oil leak on my 94 e36. What looks like oil dripping from below the rear main seal, the mechanic told me was likely coming from the housing gasket. Don't think I need the same socket but let's see when I get to replacing it this weekend.

[N0tt0N]

Excellent write up!

[Lupin..the..3rd]

Nice photos. I'm confused by these hoses though. Regular rubber hoses with worm drive clamps? Did BMW do away with the hard molded ends + O-rings + retaining clips as used on the E46?

[Jazzbass]

Originally Posted by Lupin..the..3rd

Nice photos. I'm confused by these hoses though. Regular rubber hoses with worm drive clamps? Did BMW do away with the hard molded ends + O-rings + retaining clips as used on the E46?

No, still got lots of those. The radiator, heater core and thermostat all have the typical BMW coolant connectors. It's just those connections directly around the water pump that have regular hose+worm gear clamps. Because the E90 water pump is electric, it doesn't bolt into the block like on E46 and earlier cars. It bolts to the side of the engine near the A/C compressor, is completely self-contained and has an inlet and outlet hose:



Those are the connections you see in the picture: