After a drive over the weekend I noticed the cloth braided rubber hose coming out of the top of my six is "sweating" oil. 4 or so inches of it, to be precise.

I know enough to drop my engine, adjust valves, rebuild carbs, but when it comes to flat sixes and what everything does I guess I'm not as clued up as I thought... because I figured given this goes from the top of the engine to the rear fender oil tank that it was either some kind of oil return line or an overflow line, but when I removed it the tank end is blocked off.

Hopefully someone smarter than me can tell me what it is. When I removed it I don't see any signs that the rubber has dried out or has cracks in it, but I guess I should replace it and the clamps because something's obviously going on that shouldn't be.

Oil tank to case breather hose ,it MUST be connected to the tank otherwise you will get sludge build up in your oil,I see an oil change coming up or get the oil sampled,hardly worth the risk otherwise.
Not a leak you want to leave otherwise it will make a hell of a mess of your motor,hose could be rotten if so you may need to replace it.

Thanks porschetub.

It was connected to the tank, until I took it off just now to take a look at what was going on.

I'll swap it out this weekend and do an oil change at the same time.

The tubular nipple on the oval cover has an odd feature that can cause that leak.
For some reason there is a steel ball cast into that nipple that can provide a path for
oil leaks. Especially with hose that is no longer pliable.
Make sure the second nipple on your oil tank is vented to your air filter or a catch
can. If capped it will build pressure.....and leaks

Thanks!

I think you may be right about the hose being no longer pliable though, the car was built is 1990 iirc and it seems like all of the rubber hoses have dried up and are cracking. The braiding obviously makes it impossible to know from just looking at them. I've replaced most of them but for some reason missed this one.

The last one to split 3 months ago was the fuel line into the the fuel filter... luckily I caught that spraying gas all over my driveway before I took the car out and anything catastrophic happened...

100% ,mine leaked @ that point after a short time ,what was the point of those nipples ?,surely the hose clamp will hang up on then and not compress the hose to seal it, luckily mine was long enough to cut back and sort the issue.
Thanks for bringing this up Rory as I thought my hose was faulty but it was near new.
Yes the pipe off the filler neck needs to vent,on the stock motor it went to air cleaner inlet (horn) suction side and from memory on both the 914/6 and early 911 2.0T,someone correct me if wrong.

The vent hose seems to age quickly at the crankcase end - after 4000 miles, the brand new one I put on my car when I built it has become much less pliable at that end. Seems they have a finite life...

Pelican and others are a source for correct (or correct looking!) replacement.

- Tony

PS. you mentioned: " ...but when I removed it the tank end is blocked off". Were you referring to a flame suppressor (kind of a mesh insert) inserted in line - or is the tank really sealed off there? The tank is ultimately vented to the outside world via the small pipe on the oil filler neck.

Yep @Retroracer , unless I'm missing something the oil tank end is basically a dead end. I think it's the Patrick Motorsports tank if I remember from looking at the build receipt that came with the car. It has the overflow pipe on the oil filler neck.

Oops! Hard to see perspective from the photo, but that could be the culprit.

Simply drain the oil, remove the tank and have the hole machined out.... If it is indeed airtight, you may want to give PMS a call, if nothing else, to tweak their Quality Control folks. Or, maybe they can offer an easier fix!

- Tony

You can easily test for blockage by slipping a hose over the tank nipple and blowing
into it.