Re: Oil leak questions (long) (archive)

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In Reply to: Re: Oil leak questions posted by Neil Deshpande on September 23, 2001 at 16:27:09:

"The M30 6 cylinder is renowned for oil leaks from the front of the engine. Often these leaks also create a false impression of a leaking oil pan or head gasket. Sometimes, these gaskets are leaking also...."

"The most common leak on these engines leads people to replace the timing cover gaskets unnecessarily. The leak comes from the larger of the two bolts holding the front crank sensor bracket in place. On the right upper corner of the crank pulley is a magnetic sensor used to read crank position, and on many models, RPM. The sensor is bolted to a small bracket which in turn is bolted to the lower timing case. The two bolts retaining the bracket are different sizes, one is a 6 mm bolt with a 10 mm head, the other is an 8 mm bolt with a 13 mm head. The larger of the two bolts penetrates the timing case, and oil can work its way out the threads, and leak onto the front pulley. The pulley then throws the oil around the front cover, making a mess of everything. This leaves oil sitting in and on all the little crevices and ledges, which just happen to contain gaskets, leaving the impression that the gaskets are leaking."

So I may remove and seal this bolt just to see if it does anything. Man, I wish I could get a look at one of these engines out of the car so I had a better idea how everthing fits together. If I ever have to have mine yanked (not soon I hope), or if anyone else in town does, I will really try to be present.

1. My feeling is that there can be all sorts of non-serious head-gasket leaks. I think there are low-pressure areas that are oil galleys towards the edge of the gasket that can leak and the engine will be fine for thousands of miles. A friend's iX has had this for 50k miles. No biggie. Your oil loss is normal for that motor. Another leak location is the timing cover to block mating point at the head-gasket location. The differential expansion of the head and t-cover w.r.t. the iron block causes this to open up and leak. Some hylomar is recommended during re-assembly, but again it is not a functional issue, just a clenliness one.

2. The timing covers on this engine can and do leak. They have gaskets to block, head gasket on top and oil pan gasket at the bottom. Any of those and the crank seal can leak.

3. The timing sensor is a nut that holds to a threaded staff. It does not go through the timing chain cover and cannot leak.

Thanks again Neil. Yeah, my mechanic thought leak might be from front passenger side corner of head gasket, although neither of us convinced. We degreased it and put florescent dye in the oil, and he thought the first place he saw the dye was this corner, but it may have run there or been flung there by one of the pulleys (air con most likely). There is definitely oil on top of the tensioner piston, postion sensor, air con compressor, etc. The first place I noticed visible oil after degreasing was piston and sensor. Maybe you can answer a few related questions:

1. If head gasket leak, would there be other symptoms? Compression test 190 psi all cylinders, no oil/coolant mixing, no over heating, etc. Or, if it is the gasket anyway, could it be a head bolt-torque issue or is it just a matter of time til I have to pull head - I am losing about a quart in 2k miles/3-4 months?

2. Mechanic said on S38 engine that timing chain cover is integral so it doesn't leak like in other engines - is he wrong?

3. Might it be one of the bolts that holds the position sensor - Brett Andeson says on his website this is a common source of oil leaks on the front of big sixes, but don't know if this applies to S38. Tough to trace because oil is flung everywhere by pulleys. Sounds like you just have to put silicon sealer on bolt threads. Thoughts?

While unscrewing the nuts on my 92 M5 headers, I managed to remove three studs. I could find no evidence if Loctite (or Wurth Green) on any of them. In theory studs are supposed to be of an interference design (Class 5B?) so that they are held in place by finger-tight insertion, but in practise I think most people go with Loctite, including Carroll Smith and Smokey Yunick.

I cannot imagine how the studs would cause an oil leak. They have nothing to do with oil. Check:

1. Tensioner crush washers
2. Timing chain cover
3. Front of head gasket (less likely, IMHO)

Thanks for the advice - Should I use loctite or similar on the studs, or a sealant of some kind? I have had an oil leak from the front right of the engine, which I haven't been able to trace, might it have been from the missing studs in the front?

If the threads in the head are fine, it is easy. New studs and new 9mm copper nuts (one-use). Get a 9mm swivel to put them on.

If the threads in the head are stripped helicoil. It is going to be tedious to get in there, but you could probably do it, but you'd have to remove the headers (not that big a deal, really, but lengthy depending of what else you have to get out of there). The helicoil will be stronger than the original.

My car suddenly started breaking windows for miles around today - found that the all 4 studs on the rearmost cylinder are GONE, hence the exhaust manifold pipe is floating in space, and also noticed two were missing from the front cylinder as well. Holy sh*t. Please tell me I don't have to pull the engine or the head... It looks like they just fell out, not snapped off. Any info/advice much appreciated!

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