Mysterious Oil Leak Help 94 540i

Hi,

I have a oil leak somewhere that only shows up at high speed. 80 mph or greater and oil blows back on to the exhaust and smokes pretty bad as it burns off. Under 75 mph no oil/smoke. I get no drips on the garage floor and have been unable to identify the source of the leak. Darndest thing I've ever seen. I have replaced valve cover gaskets but this hasn't cleared it up. Also checked oil filler tube but it doesn't seem like thats the problem. Any ideas would be much appreciated. 160,000 mi E34 540i

Welcome,

Its pretty unusual to something like that that shows up at speed, rather than RPM.

Are you absolutely sure it's motor oil? I would have thought the valve cover job would have sewn that up. Since it's variable, perhaps its the PCV valve at the back of the block. It's supposed to separate oil from vapor, and when it goes it does funny things like whistle, weep oil and smoke. PITA factor is high since it might not be it, but on the bright side you can soak the old one in some gas to see if it's it, before you buy a new one.

Otherwise, oil sometimes comes out the back "crescents" on the valve covers, and the only thing that cures it is gobs of permatex red.

Also, it sometimes accumulates in the "valley" of the block. If so, oil will be plainly visible on the torque converter when looking from above with a flashlight.

You could take a look under the oil filter reservoir as those o-rings eventually bite through the hoses.

You mentioned "oil fill tube." We don't have one of those. We have the cap on the passenger side of the block, and if that seal on the cap is shot, that could be it. If you mean the oil level tube, that thing is bulletproof.

You didn't mention if it was stick or automatic. If automatic, the pipes flank the tranny, and any tranny fluid leaks have a tendency to drip right on top and burn rather than dripping on the garage floor. Same with the tranny fluid cooler lines, at the back of the block underneath the coolant reservoir.

I suppose you could have a leak on the upper half of your timing chain covers, although I have a hard time imagining how it would start.

Power steering fluid is always leaking somewhere on these cars.

More Clues!

Oops, yes I meant the Oil Level Tube.

I'm pretty sure its motor oil. It is an automatic, but the fluid on the exhaust is on the bottom of the exhaust not the top. It is definitely runnig from the front onto the back, down the tranny fluid cooler and blowing back onto the exhaust. I'll check the hoses to the cooler again. This was my first guess but it didn't seem like it was coming from there when I looked

I have checked around the valve covers again with my little mirror and flashlight. Those "crescents" at the back are not leaking, in fact since the new gaskets went on, it is dry all around the valve covers.

The way it is traveling I also thought it might be the rear engine seal but if that was so I imagine the flywheel would be wet with oil. Besides these seals almost never leak.

PCV valve replaced 2 years ago. I hope it is not that.

I know it is almost impossible to diagnose something like this over the internet. I just thought someone might have an idea. And, you may be right about it being rpm related. I figure that 80 mph may just be the speed at which there is enough wind to blow it back onto the exhaust. Of course the upside is that if I drive it so that I don't have oil smoking, I won't get speeding tickets. At least not BIG ones. The thing runs like a scalded dog.

This is just one of many issues I have to figure out with this car to put it back in shape. Next is sloppy stearing and then my infamous "only in cold weather check engine light". Alot to do but I just can't part with it. I'm not as fond of the E39s.

Thanks Tim

J....

Now, I don't have that much experience with the V8s, but I did just finish my first alusil block replacement on a '94 540iA, and the motor was resealed at that point. So, take this for what it's worth.

Here's what I think: there's an oil return line that runs under the intake, parallel to the coolant lines. It fits into the rear bottom of the PCV plate. It has O rings and such that can leak.

EDIT: Hmm...actually, now that I think about it, it's held in place with some kind of funky fitting. Been a few weeks since I put it together...

Edit #2: Oh yeah! And, I'm sure you checked this already, but FWIW -- don't forget to inspect the rubber caps on the rear of the PCV plate. Lord knows anything could happen to them and cause all sorts of nasty surprises...

Now, if the motor has a lot of blowby, running it at high(er) RPMs, consistent with the prognosis, would result in leaks from that line. The only question is: how is the oil traveling from the bottom, forward edge of the PCV plate to the trans heat exchanger lines (regardless of the inherent high airflow through the engine bay at speed)?

Carefully inspect the cooler lines. They leak, and when they do, replacement's a bitch. We'll talk about that if it becomes an issue.

First, though, I'd try to get a look under the intake and see what's going on with the oil return line.

best, whit

We gotta get this sorted out cause we can't have you driving around in a 540 that smokes when it goes 80 now can we? Post a pic.

Here are some pics if I didn't goof them up trying to post them. Thanks for the suggestions from you and Lowell. I won't have time to get back into it til next weekend while I'm doing a complete front end overhaul (tie rods, center track rod, control and thrust arms). This should take care of the sloppy steering and shimmy while braking. Man I wish I had access to a lift.

Any way, I'll check things out and get back with you. Thanks again.

Good suggestions. I'll check it out next weekend. I posted some pics in my reply to tim.

Thanks and I'll report back with what I find.