Oil overflow tube - need some help understanding

[Christien]

1972 oil system, 1982 3.0L engine, K&N air filters/hats on Webers. So we have a bit of a mixture here to say the least

Here's the story: when I first bought the car with the original engine, it also had the original airbox, which the overflow tube attached to. When I converted to the air hats, I (stupidly) just left the tube dangling. Now, the car has always leaked a bit of oil, so I didn't really think anything of it until just recently, I figured I could probably clean up a lot of that by having the oil overflow land in a catch-can somewhere, so I rigged up an old aluminum water bottle as a temporary measure to test this. But in doing so, I made it more or less air-tight, so the overflow really actually has nowhere to go - I can hear sizzling inside the aluminum bottle. This (I believe) has caused a massive oil leak - as in, leaving a solid trail behind the car, and then losing probably 2-300mL of oil on the garage floor within 10 minutes or so of shutting the engine off. It's possible I sprung another major oil leak at exactly the same, time, but I'm guessing it's because now there's nowhere for the overflow to go, so it's coming out the bottom somewhere.

I don't really understand the idea of the overflow, and where it's supposed to go, even going back to my original airbox - did it just collect in the bottom of it? I don't remember there ever being a puddle in there.

What can I do to allow airflow from the overflow tube, yet still not have oil dribble all over the top of the engine?

Thanks.

[john walker's workshop]

It's a breather, not an overflow. What is the oil level on the stick? The catch can should be vented in some way.

[Christien]

There's a breather and an overflow, at least I've always read/been told the 2nd hose is an overflow. In my case, the red hose is the breather, the grey is the overflow. Oil level is good, a bit lower than halfway.

[E Sully]

You have a crankcase breather, and a vent to the intake. No overflow. There is a normally a drain from the intake housing to let oil that accumulates drip to the ground.
What you are calling an overflow is a vent to bring gasses to the intake to burn off the gasses. Think PCV. Putting that into a sealed container is going to pressurize the oil tank and crankcase.

[Christien]

So was the grey hose routed into the original airbox a source of fresh air then? Can I just remove the hose and let it breathe? Presumably I'd need a filter of some sort over the opening, right?

[john walker's workshop]

The '72 I just got has a small K&N filter on the higher outlet. No leaks yet, but I'll be installing a catch can and hose. The lower one goes to the top of the engine.

[E Sully]

The grey house went to the intake, but to bring dirty gasses from the crankcase and oil tank to be drawn into the intake to be burned by the engine. That is one of the problems with overfilling the oil in 911's. The excess oil would end up in the airbox, some being drawn into the intake causing excessive smoke, and some dripping to the ground from the airbox drain line.
Porsche made sure that the cars could mark their territory even if you sealed the engine perfectly.

[Christien]

So would I be best to just drill an air release hole into the catch can, and leave the catch can attached?

[john walker's workshop]

Yeah.

[zedsn]

I have a cheapo anodized catch can from ebay that I drilled and tapped a couple of fittings and put a K&N style filter out of the top for a breather in my 914 motor so I would think an ebay one could be made to work for you.

[Christien]

Could you post a pic of that please?

[zedsn]

Here is what I put together and the breather was put on the top later to give you an idea. The bottom unscrews to let any oil out that has collected.