Air Oil separator 911/996

[Hilux2400]

I am getting a bit of sludge on the underside of the oil filler cap. It's nothing serious and I think it's fairly consistent with cold damp weather and not an unusual feature of this engine where the oil filler cap is in fairly cool location.

I have been thinking about cleaning out the air/oil separator and its connecting tubes. There's no mention of this procedure in the w/shop manual or service schedules. Has anyone done this and if so was it worth it?

Hilux

[911944]

Got a similar problem on mine.

But underneath my water tank, there's a breather pipe that's blanket off. My last one wasn't?

Been fine for the last 15,000 miles....

[Magic919]

Probably caused by dirty throttle body.

[Rockster]

Hilux2400 said:

I am getting a bit of sludge on the underside of the oil filler cap. It's nothing serious and I think it's fairly consistent with cold damp weather and not an unusual feature of this engine where the oil filler cap is in fairly cool location.

I have been thinking about cleaning out the air/oil separator and its connecting tubes. There's no mention of this procedure in the w/shop manual or service schedules. Has anyone done this and if so was it worth it?

Hilux

There is no AOS cleaning procedure because the AOS doesn't need it. This is because the AOS doesn't collect any thing that needs to be removed/cleaned away.

I guess in some ways the AOS is self cleaning.

The "sludge" you see is normal given that under the cap is the coolest place in the entire engine and its crankcase vapor area.

Water boils out of the oil and this water vapor rises and part of it goes up the tube where it cools and condenses under the cap. Some of the water that collects under the cap and on the walls of the tube directly under the cap drips down but some mixes or is mixed with oil vapor and the sludge you see is the result.

Harmless relatively speaking.

But it does highlight the risk that arises from letting the engine go too long between oil/filter services. Regular (and in this context timely) oil/filter services drains the oil water contaminated oil out of the engine -- because the only way to get all the water out of engine crankcase is to drain the engine oil from the crankcase -- and replaces this drained oil with fresh oil.

[Hilux2400]

The car had had many short journeys and then a motorway run of about 100 miles soon after an oil and filter change. There was quite a lot of emulsion which I cleaned off, but it has not happened again with the same intensity. I have not noticed any water loss or oil mixture in the header tank so I figured it was just condensate which I know is a feature of this engine with a high and long filler tube in the coolest spot.

Hilux

[sportsandclassic]

911944 said:

Got a similar problem on mine.

But underneath my water tank, there's a breather pipe that's blanket off. My last one wasn't?

Been fine for the last 15,000 miles....

Hi, is the rubber pipe about an inch in diameter? If so it is for an air pump. They did not all have this and was most common on a replacement engine being installed but car not having air pump.

Mike

[anonymous-user]

Hilux2400 said:

The car had had many short journeys and then a motorway run of about 100 miles soon after an oil and filter change. There was quite a lot of emulsion which I cleaned off, but it has not happened again with the same intensity. I have not noticed any water loss or oil mixture in the header tank so I figured it was just condensate which I know is a feature of this engine with a high and long filler tube in the coolest spot.

Hilux

It will happen with most cars used for short trips and long oil change periods. Doesn't happen if oil is changed regularly and car is only used on long runs.

If you can't avoid short trips, change the oil more frequently.

[911944]

sportsandclassic said:

Hi, is the rubber pipe about an inch in diameter? If so it is for an air pump. They did not all have this and was most common on a replacement engine being installed but car not having air pump.

Mike

Hi, yes that's the one! Thanks for that. So is it likely my car had a replacement engine?

[sportsandclassic]

911944 said:

sportsandclassic said:

Hi, is the rubber pipe about an inch in diameter? If so it is for an air pump. They did not all have this and was most common on a replacement engine being installed but car not having air pump.

Mike

Hi, yes that's the one! Thanks for that. So is it likely my car had a replacement engine?

It is possible or they may of had engines to use on the production line that were all plumbed for secondary air injection pump.

[911944]

Thanks for that. It can't be the Porsche factory, surely they wouldn't just put a blanking plug in secured with a jubilee clip?

[sportsandclassic]

Most do not even have a jubilee clip. Just a blank plastic plug.

[General Bilko]

Hilux2400 said:

I figured it was just condensate which I know is a feature of this engine with a high and long filler tube in the coolest spot.

Correct. This happens with my 996 C4 and is nothing to worry about AFAIK. I use mine for a 20 mile commute (i.e. 40 mile round trip) and it makes little difference whether the oil's just been changed or not, the main difference is the weather, it's worst in the winter and there's almost nothing in the summer.