If you have a leak at the front of you 3.5 liter engine, read this...

[Robert K]

One place the 3.5 liter engine is notorious for leaking oil is the two bolts holding the crank position sensor bracket to the front of the timing chain cover. This weekend, I decided to do what I could without having to take the harmonic balancer off to try to fix this problem on my engine. Since the bottom bolt is very hard to get to, I removed the A/C compressor to get a little more room to work. This was accomplished by removing the lower adjusting bracket and removing the top pivot through bolt. You'll also need to remove a small clamp that holds the hose to the frame rail so that the hose can move. This bolt and bracket is easily accessed once you remove the air filter box. Once the A/C compressor was off, I also unbolted the crank position sensor. Then, I took the top crank position sensor bracket bolt all the way out and cleaned it thoroughly with carb cleaner and let it dry. Using an end wrench, I backed the bottom bolt out until it hit the back of the harmonic balancer. With it out as far as it would go, I took a small paint brush and sprayed it with carb cleaner. I then repeatedly rubbed the areas on both sides of the bracket where the bolt and block would seal against it until I thought they were clean. When I had it as clean as I could get it, I also let it dry. Then, with a small paint brush, I applied some of the shellac type of gasket sealer to all of the surfaces that would be sealing the oil in. Then I put the top bolt back in and tightened both bolts down tight. After 200 miles, it looks like all the work took care of the leak. Just thought I'd pass this one on in the event anyone else had a similar problem.

P.S. In case you haven't read my other post, I also have an oil pan gasket leaking. Ugh!!!

Grace and peace,

Robert K
1991 535i

[howardc64]

Using the excellent info from Robert, I was able to stop my leak. I did a simpler but a less thorough job than Robert's instructions. Never the less, the leak was stopped.

I just tightened the 2 bolts holding the crank position sensor bracket. Top one was easy to get to after removing air filter housing. I got to the bottom one with an open end wrench positioned over the top of the AC compressor without removing it.

Here are a couple of pics





Remember to gap the crank position sensor properly after tightening. I found tightening the bolts on the brackets changed the gap. Since the gap is only 1mm, changing the gap can cause actual contact between the sensor and the teeths on the harmonic balancer.

The leaked oil would accumulate just below the bottom bracket bolt (lowest point). Looks like it would drip onto the AC compression brackets and eventually work toward the lowest point on that.

I also had leaks in the oil pan gasket. The bolts were awfully lose (dealer replaced the gasket 2 years ago). Not sure why they would have loosened? I just tightened the bolts a bit and the leak stoped here as well.

[pundit]

Yep! That's a common M30 problem.
Mine had the same leak when I bought it.
I fixed it after finding the answer on the web.
The owner had been told it was the timing seal!
Very easy to misdiagnose as the oil drips down onto the harmonic balancer and then is flung off giving the appearance it coming from the timing cover seal.

[bahnstormer]

yup yup my mech was fam enough with the m30 to know that it wasnt anything
serious and just tightened those bolts up a little...

the oil pan gasket is common too

[winfred]

biggest m30 leaker i see is the damn oil pan bolts backing out, check em every oil change

[BFEINZIMER]

i think i may have thim, im gonna clean out the entire engine compartment to see if i can trace it to this spicifically

[BigKriss]

I've never checked mine but I will do.

biggest m30 leaker i see is the damn oil pan bolts backing out, check em every oil change

[Anton CH.]

biggest m30 leaker i see is the damn oil pan bolts backing out, check em every oil change

Why not just locktite it?

[wjbell]

biggest m30 leaker i see is the damn oil pan bolts backing out, check em every oil change

Yeah, as you and others have said, the oil pan bolts just back out. Right after I bought my car I was changing the oil and just happened to look at the pan. Bolts in the front of the pan had backed themselves out so far they fell out of the threads and were resting on whatever surface was right below them. I'm surprised there wasn't a leak!

[winfred]

no reason, go for it

Why not just locktite it?