AOS, The Final Solution
 

I replaced my AOS about 12 months ago, it lasted about 2 years although I feel that it is starting to fail again. I put this down to an older motor (I have a 2000 S) and the increased blow-by straining the AOS more than it was designed for with a new motor.

I have read that this could be a PCV valve problem so i will get that looked at. The car is going to the mechanic tomorrow for some major work (clutch, flywheel and mounts along with spark plug tubes and a normal service) so it will be seen to then. This I see as an interim measure however.

Now... the solution I have in mind is to go down the road of a breather tank and a belt-driven vacuum pump which I will have plenty of space for when I remove my ac compressor (ac isn't working btw so no loss there). I realise this will vent to atmosphere but it is not an issue where I live as we have no smog tests or even regular vehicle inspections. Also, I suspect the vehicle would pass an inspection anyway as long as the tank looked OE.

My question is, what hoses would I have to connect and where and which ones can be decommissioned? Also, what about the PCV valve? Would it now be redundant? Another thought I had is attaching a hose to the drain valve at the bottom of the tank and plumbing this into the oil return hole that the factory AOS uses. I could then empty the tank straight back into the sump by turning a small tap rather than messing around with buckets and pans. Is this realistically possible? Are there any other tips or suggestions in going down this road?

I really just want to make the system as simple as possible and maintenance-free, save for draining the can as often as is necessary. Every time I do an AOS it costs me around $150 for the part and another $450 in labour so purely from a cost-saving perspective this is a good investment. The fact that I won't be blowing smoke again and the (possible??) power increase are welcome by-products.

Thoughts?

Would it be simpler just to learn how to do the AOS yourself? It isn't as if it requires a lot of exotic tools or some great diagnostic skills. Just some contortions to get things connected right.

While AOSs can fail quickly, many run for 5+ years. Mine was 10 years old when I sold the car.

So balancing the risk of the unknown via the bypass against the 2 hours to do an AOS ...

Not to mention we all live on the same planet ...

Your car, your choice.

Instead of the whole vacuum pump system couldn't your own design AOS use an engine vacumm line to suck the oil back into the engine without all the complication of the vacuum pump?

As far as the AC discharge if you go that route, offset by eating 3 steaks more than usual (Thereby killing a cow and reducing one of the top methane sources of global warming)

I don't think my 2001 has ever had an AOS replaced so they can last a long time.

Perhaps there's another underlying issue.

I've got this
JEGS Air Oil Separator - JEGS
It's plumbed into the line from the stock AOS to the intake. I've got it mounted in the trunk, so it's easy to empty.

I looked at the vacuum pump route. some folks repurpose a bmw SAI pump to draw vacuum on the crankcase (that way electric not belt-driven). otherwise you have to find a pump that can handle grimy oily medium. another solution, if you are committed to emptying a catchcan regardless, is to route the output of the aos through a catchcan and into the intake as per usual. this way you have a backup if the aos fails (ie, the catchcan) and can tell if the aos is going by the rate the catchcan fills. there is a guy on this forum if you search that repurposed the air conditioning dessicant tank as a catchcan and said it worked great. otherwise, take a look at the aftermarket aos solutions available for subi wrx sti's - you might be able to repurpose one of those. there is also the option of the motorsport aos which is supposed to be more robust. finally, there is some thinking on this board that a failed pcv valve might be the cause for premature aos failure.

edit to add that it looks like mr. fro beat me to some of it!

This could be a good option for you if you want to get rid of the AOS. I'm interested in hearing more about this... You have any pics j.fro?

Thanks for the tips everyone.

My car is now with the mechanic, I pick it up on Monday. I have asked him to check the PCV valve and based on whether or not it looks like part of the problem I will make a decision on how to proceed.

By the way, I didn't mean to cause a stir on environmental issues, so I apologise for that. It is actually quite refreshing though, since the "American Stereotype" here in Australia is the SUV or big block Chevy driver tearing down the highway burning sub two bucks a gallon gas.

In Aus we pay about 6 dollars a gallon and it includes a carbon tax, so we are theoretically buying our way "green". My wife and I also include walking and taking trains in our transportation mix so I don't feel at all guilty about a little oil vapour venting to atmosphere considering that I drive far less than average and make great efforts towards conservation in other areas.

I shall post my mechanic's comments on Monday and see if he has any insight or ideas regarding the AOS system mods.

This looks like a good solution jfro and the first time I have seen it. :cheers:

FYI: The #1 reason for premature AOS failure is oil overfill after an oil change . It kills em quick. Mine is 15 yrs old, still original and functional with over 100k miles.

Here's a pic of my piggyback AOS. The o-ring at the drain started leaking, thus the bit of paper towel in there.
http://986forum.com/forums/uploads01...1374352103.jpg
And a pic of the engine. You can see the plumbing in the upper left corner. I cut the fitting end off the Porsche AOS and screwed in a brass fitting for the hose. Did the same on the intake tube. There was another smaller vacuum line that needed to be spliced in, so I used a brass T fitting.
http://986forum.com/forums/uploads01...1374352539.jpg

The *real* issue is:

The canister does not have enough time to drain the oil back into the engine. Porsche proved this when they released the 996 3.6 AOS (people mistakenly call it the Motorsports AOS) The ONLY difference between it and the stock AOS? The capacity. It holds more oil and gives the oil more time to drain back into the block before being sucked back up into the actual diaphragm.

I have seen a LOT of failed attempts and FAILED engines with people trying to "outsmart" the OE system. Yes, failed engines.

Few people realize you *need* to pull a vacuum on the engine. The AOS does this. I cannot keep track of how many I have seen completely blocked off, or a "puke" can put into place. Many people don't understand that the OIL needs to go back INTO the engine :) not just to a puke tank that keeps overflowing!!

The 2.5 engines have a LOT less issues than the 2.7/3.2/3.4/3.6/3.8. The little 2.5 only spins 6400 whereas the larger engines all spin 7200+ This RPM difference plays a big factor into the air being displaced on the back side of the pistons.

I have thought long and hard about this, I have a prototype system, that does use a LARGE catch can, but I'm pulling a vacuum on it like the stock system. I'm also using a diaphragm that is identical to the Porsche diaphragm, but $42 to replace (and it takes 10min. to replace)

If I **thought** their was a huge issue.. I'd make them, but right now, I don't see selling more than 8-10 of them over a 6month period.

I'll save it for my customers.

I know this thread is about a hundred years old but I have a 986 S autocross/track car that acts like a mosquito fogger after a fast lap. Noting Brad’s comment above regarding the 996 3.6 AOS, I’m wondering (a) will it fit/work on the Boxster and, if so, (b) does it cost less than the diamond-studded Motorsport version?

If you're running a deep sump, you might just drop the oil level a couple of bars, there's still lots of oil in there. Works for me, no more smoke bombs.