Robert K
01-30-2006, 12:19 AM
I've always had an oil leak on the front of my 3.5 L engine in my 1991 535i. Last year I put a new pan gasket on because my other one was squeezed out at the front. That took care of that leak path. But, I still had another. Turns out it was the two bolts holding the crank sensor bracket onto the front of the engine. If you take the air filter housing out of the car, look down towards the crank pulley. You'll see a large, round part with large teeth around its circumference. That's the harmonic balancer. Right above the A/C compressor, you'll see a little bracket with a small, round part that sits right over the teeth on the harmonic balancer. That's the crank position sensor and the bracket in question. There is one 10mm bolt and one 13 mm bolt that hold this bracket on. The problem is that these bolts protrude into the timing chain area, which has oil in it. These bolts also have a bad habit of loosening up, which causes the leak.
To work on this problem, it's best to remove the A/C compressor brackets and let then remove the compressor and let it hang. That will give you access to the crank sensor bracket. The top bolt (13mm) is relatively easy to get out. The bottom one (10mm) actually can't come out because the harmonic balancer won't let it. The best thing you can do is remove the top one and back the bottom one out until it contacts the harmonic balancer. Now get a couple or really small cheap paint brushes and use your favorite cleaner to clean around the bolts and all the sealing surfaces the best you can. Once I had it as clean as I could get it, I coated the surfaces with gasket shellac and put the bolts back in. Tighten them both down as tight as you can get them without going so far as to break them off. It might be best to let the car sit overnight without starting it to let the sealer dry out a bit.
I actually did this same procedure to the same bolts a few years ago. I suppose over time, the bolts loosen up. I'm hoping this will last for a bit. I also hope this helps someone else out there with a 535i that has a mystery oil leak. This happens to be one case of poor German engineering. But I suppose the rest makes up for it. :)
Grace and peace,
Robert K
1991 535i
To work on this problem, it's best to remove the A/C compressor brackets and let then remove the compressor and let it hang. That will give you access to the crank sensor bracket. The top bolt (13mm) is relatively easy to get out. The bottom one (10mm) actually can't come out because the harmonic balancer won't let it. The best thing you can do is remove the top one and back the bottom one out until it contacts the harmonic balancer. Now get a couple or really small cheap paint brushes and use your favorite cleaner to clean around the bolts and all the sealing surfaces the best you can. Once I had it as clean as I could get it, I coated the surfaces with gasket shellac and put the bolts back in. Tighten them both down as tight as you can get them without going so far as to break them off. It might be best to let the car sit overnight without starting it to let the sealer dry out a bit.
I actually did this same procedure to the same bolts a few years ago. I suppose over time, the bolts loosen up. I'm hoping this will last for a bit. I also hope this helps someone else out there with a 535i that has a mystery oil leak. This happens to be one case of poor German engineering. But I suppose the rest makes up for it. :)
Grace and peace,
Robert K
1991 535i