Last930

Will an air/oil separator failure trash the cats and O2 sensors? The car was hit in the rear; it was driven home and then to the body shop. After the repair was done the car started to smoke a lot and dump oil out the muffler. Would the cats be shot by a problem like that if it was only run a few minutes? If so, what is a good source for replacements?

Macster

Can't say for sure but probably not.

My Boxster suffered two failed AOS's with the 1st one ending with oil dripping out of the exhaust tips. The 2nd one ended with just heavy smoking for about a minute at idle.

Both still work ok but one is "weak", due to I think the brick is a bit loose. The thing works just fine most of the time but in cooler weather generates a P0430 error code.

The 1st AOS failed at around 80K miles, the second at maybe 160K miles. The 3rd is ok still over 100K miles later. Total miles? 270K.

'course I have to mention if you run an oil heavy with ZDDP this possibly can kill the converter. The phosphorus in the additive coats the working surfaces of the converter and kills it.

For replacements if they are needed a good source in that you get the exact item that the car came with from the factory is from your local Porsche dealer parts department. You're going to pay though. $1000 or more per side not including labor to remove the old ones and install the new ones.

If you want to cut costs (maybe) you can try to find some from a Porsche salvage business. Oklahoma Foreign (in Oklahoma City I think), or Parts Heaven (here in Hayward CA) are two the come to mind but there are others. Check out the ads in Panorama and Excellence.

Last930

Thanks. I'm looking at a project Boxster that had a recent aos failure that dumped enough oil throughout the exhaust that the oil dripping out of the exhaust actually started on fire!

Macster

Well, you can't know until you get the AOS fixed.

Follow directions on the bottle but run one make that in this case two bottles of Techron through the engine. When the last fuel tank with Techron gets down to 1/4 tank change the oil/filter.

Then just drive the car. If one or both converters bad you'll know by the CEL and error codes.

Oh, be aware that in a few cases some engines with an AOS failure that progressed to the raw oil coming out the exhaust pipes phase suffered from a hydrolocked engine. In fact mine did as the dealer Porsche tech was doing a compression test (?!!!) on the engine prior to fixing the AOS. Luckily the lock up occurred when cranking with the starter so no damage was done.

But this is not always the case. The engine could have head gasket issues, possibly even a cracked head or block.

So like I said be aware...

Last930

I'll have it towed to the mechanic's place. He just replaced the aos on another Boxster so he's good to go. His opinion is that the cats shouldn't be ruined by a one time issue like this, but won't know for sure until it's driven for a while. This car was running when it started leaking so I don't think it would be hydrolocked, but we'll play it safe before starting it. Thanks for the advice!

Macster

The AOS was failing and routing a lot of oil to the engine as the engine was running. Then the engine is shut off. There is a lot of oil in the intake. This oil runs down and into the cylinder if the intake valves are open. Or collects on top of the closed valves.

The engine is cranked and the cylinder experiences hydrolock immediately. Or the engine turns over 1 maybe nearly 2 revs and possibly fires then the cylinder with oil its intake valves pulls in a slug of oil. Then the engine hydrolocks.

Best to remove all plugs and then crank the engine to remove any oil that may be in the intake and made its way to the cylinders.

At this point I'd replace the plugs too. I do not think it a good idea to reinstall these plugs.

gfl

Of course the answer, technically, is "it depends", but we can apply some logic.

Oil through the exhaust will, over time, kill a cat. But let's look at reality. My mom's old Audi A6 burned 1 Qt/1000 for 150k miles - still has the original cats. That's 150 qts + through the exhaust.

In fact Porsche's spec for excessive consumption is somewhere under 1000 mi/qt. Ask Gundo.

An AoS that failed and was driven say 50 miles?

I'll go way the heck out on a limb. No.

Grant

extanker

i would bet the cats will be fine. i think that after the repairs they will start the car up and let it idle for 15 minutes or so then drive it easy until no smoke. the cats get hot enough to burn the oil off and hopefully the 02 sensors too

gfl

When mine "failed" it was really a few smoke-screens at the track. I continued to track it and drive it 3 hours home with no smoke, and changed the AOS 3 months later at my convenience.

WTF happened to yours?

Grant

Last930

Thanks for all the advice; I bought the car and had it towed to my mechanic's shop. He will replace the aos next week and see what else it needs. If the cats are ok this may turn out to be the buy of the year.

Macster

There are if not different failure modes different failure phases and the AOS (at two different times) in my car got into a more severe one than your AOS.

Also, I have to question your diagnosis. If there was just a few smoke screens at the track this is not real sign of AOS failure but a result of the car's oiling system's inadequacy which overwhelms an inadequate AOS, momentarily.

In the case of the AOS failures with my car, both times the engine smoked quite heavily from start and continued smoking, for minutes the 1st time, and for about a minute the second time. The 1st time there were other symptoms: the engine idle speed that was up and down with maybe --I can't recall now -- maybe a rough running engine. I had to run the engine a few minutes to pull the car out of the garage and get it out into the street and properly positioned for the tow truck and there was a lot of snow on the ground and the car got stuck in a snow bank made by the snow plow at the end of the driveway. I was holding my breath the whole time and while was aware of the engine was less focused on symptoms at that time and more focused on getting the car set up so I could shut off the engine.

The 2nd time the engine ran smooth enough after a cold start but smoked like a mosquito abatement fogger for around a minute or so then I shut off the engine and called for a tow truck.

So really while you replaced the AOS that you could do so are your convenience I think strongly suggests the AOS was not bad. I guess I could have waited 3 months to replace the AOS too, but I would not have been able to use the car in those 3 months.

Oh, in the 2nd AOS failure I cut apart the AOS and found the reinforced diaphragm had a split in it that looked like it was due to material fatigue. I never got the 1st bad AOS from the dealer.

Last930

The good news is the cats seem fine. Once the aos was replaced and the engine run a few miles the smoking went away, for the most part. A new problem cropped up that didn't exist prior to the aos failure - an oil leak seems to have began at the bell housing side of the engine. Can't know for sure if it's the rms or imb seal, but it drips out a few drops after it's run for awhile. Can the aos failure create enough vacuum to ruin the rear main seal?

Macster

Unlikely the AOS failure created enough vacuum (low pressure) to ruin the RMS. What is more likely is it was masking a marginal RMS by making the seal seal better.

Now the engine experiences something near normal pressure (still low pressure though as that is the intended result) the marginal seal has made its presence known.

Last930

I have put about 500 miles on the car since the AOS was replaced; these cars are a blast to drive! The engine still drips a little oil, so it's going to the shop next week for new clutch, rms and LN int shaft bearing. I'll get new front tires too, as the ones on now are pretty scalloped on the inside. The car was aligned a few months ago so I'm hoping that the new tires will hold up. There's a couple more odds and ends it needs, then it should be in pretty nice shape.

PelicanParts.com

Dave - sounds like you're enjoying your new Boxster aside from the leak. Keep an eye on continued oil smoke emitting from the exhaust. Any pictures of the car - post 'em up!

Here's a helpful guide to potential Boxster engine issues which is a good read just for the info itself even though you have a mechanic doing the work. Check it out: Common Engine Problems & Failures

Mark/Pelican Parts