jpooley

TL;DR Smoking out tailpipe after PCV replacement. Do I really need a new engine?


I purchased a 2012 Cayenne base last fall with 193k miles. “That’s a lot of miles,” you might say. But it was in pristine condition, inside and out. I took it to a local Porsche mechanic who told me he had to check the odometer three times because he couldn’t believe it had that many miles.

Fast forward a couple of months, and I get a low oil warning. Granted, we do drive this car a lot—probably 5k miles before the light comes on. I add a quart of oil, and I’m back on my way!

Three months later, I’m back at oil minimum, again probably 5-10k miles. The same mechanic says we might have an issue and to add another quart.

A few more months pass and a few thousand miles, and we’re back to oil minimum. The mechanic says it’s likely the PCV valve, so we get the whole PCV unit replaced (it’s all one piece with the valve cover) along with an oil change.

Keep in mind: no smoking ever up to this point.

I pick up the car thinking I’m good to go! The mechanic tells me that the intake had a lot of oil in it when they pulled it off to replace the PCV. He said the spark plugs were all great, and when they looked down into the cylinders with a camera, they all looked amazing as well. They ran Seafoam through to clean anything out as well.

We drive the car around town that day and then 2 hours north the day after. While visiting up north, we pull over to the side of the road for about 10 minutes with the engine running. (Still no signs of any issues up to this point.)

As we pull away, the tailpipe starts to dump a lot of smoke. It looks pretty white. No engine lights or shaking—just embarrassing smoke. It only lasts a few seconds, so we keep driving. We get to the next intersection about a half mile down the road, and it smokes a lot while we’re at the red light. As we drive through the intersection, we can feel it shaking a bit but still no warnings or lights. We pull into a parking lot and shut it off.

I text the mechanic, who says it might just be some more Seafoam making its way through. After sitting with the car off for about 10 minutes, we start it back up: no smoke. So we start on our way home. We stop one more time about 10 miles down the road at a grocery store, and it smokes a little more. This time the engine light comes on briefly, then goes away. I have a little Bluetooth scanner, so I plug it in and read P2271 - O2 Sensor Stuck Rich. Seems right, given the smoke. The mechanic texts back and says to keep driving it unless the light stays on or is flashing.

The next two days go by with a little smoke here and there, mostly around town. We just assume it’s the Seafoam.

Three days after getting the car back, we take a trip 4 hours south for Mother’s Day. Halfway through the drive, we get the oil minimum warning. We had probably only driven a couple hundred miles since getting the PCV replaced, much less than the 5k miles between adding oil before the PCV replacement. The mechanic tells us to add a quart and keep him posted. We add the quart, which brings us back up to full bars on the digital dipstick, and make the rest of the drive. When we arrive at our destination, the oil level is 2 bars below full.

The next morning, I notice oil on the driveway. Looking under the car, I find oil dripping all over. There were zero leaks or signs of leaks before this—super clean underside. I start looking all around, trying to see if I can find where it is coming from. I eventually look inside the air box and find it full of oil! The filter itself was half sponged up with oil. It looked like it had come up through the small port in the bottom of the air box. After removing the air filter, I wiped out probably a cup (1/4 quart) of oil from the box, and it’s obvious this is where everything on the underside of the car and the driveway was coming from.

I call my mechanic back home, who says I need to take it to a local shop to get it looked at. He’s not sure what’s going on and is really confused by the oil in the air box.

I find a German autos place that is able to get me in a couple days later on Monday. We don’t drive the car in the meantime.

The second mechanic looks at it and says that the replacement PCV isn’t an original part and must be causing the issue, although he couldn’t really explain the oil in the bottom of the air box. He says it could have worked its way back through the intake. However, the oil was all at the bottom of the box, not the top where the intake hose is located. The second mechanic replaces the whole PCV unit again.

Believing our ordeal is finally over, we pick up the car and head home. The drive is 99% freeway. We don’t get any smoke, shaking, or lights. The next day, as we’re driving around town, you guessed it—smoke.

We call the second mechanic, who says it might just be some leftover stuff burning out, so we keep driving around. This is my wife’s daily driver, so it’s mostly used to run kids around or on errands about town. Over the next week, it has its little episodes where it smokes for a few seconds, mostly while stopped at red lights. It’s not every day or every time it is driven. Never on startup. The rest of the time, it runs normal. Only once did it smoke a lot, shake, and flash the engine light three times. Scanned again, and it said cylinder 1 misfire.

I call back the first mechanic, and he’s able to get me in to check it out. He pulled out and checked the spark plugs and the plug for cylinder 1 was fouled. He does a leak-down test: good. A compression test: great. However, he found that there was no pressure in the crankcase; the intake has all the vacuum. His hypothesis is that this is causing oil to be sucked up and burned in cylinder 1. He did say, “I’ve never seen this before,” which makes me question his suggested solution of a new engine.

Any thoughts? Has anyone seen this before and understand the underlying cause and issue? Valve stem seals? Oil consumption was marginal before the PCV “fix.” Why no smoke or issues before the new PCV? Is a new engine really my best option?

jpooley

Pictures are worth 1000 words.


Oil in air filter

Oil in air box

geetee

Take off the pipe at the TB. Is there oil there?

jpooley

There was oil in the pipe during the second PCV replacement. I remember the second mechanic telling me that they cleaned out the pipe and cleaned the TB. I'll pull it off again tonight and see if there is more in there. I have checked the air box side and air box itself and it's been dry.

jpooley

Just checked the TB side. Oil present.

garrett376

If your air filter is oily, you'll certainly find oil everywhere that connects to the filter!
There's something off with the PCV system... did you replace the PCV Valve with a factory part, or aftermarket? Before I thought about an engine replacement, I'd be replacing that part... with a different mechanic perhaps!

jpooley

The second mechanic claimed that the first replacement PCV was not factory but that his second replacement WAS factory. I can’t say for certain.

Air filter has been and is still totally dry since the second PCV replacement.

geetee

PCV replaced twice? Can't say it's never happened before with parts but any chance both PCV's were bad?
I'd install a oil catch can between the PCV and intake manifold. See how much oil you're collecting after a drive. That should tell you if you're dumping oil from the PCV into the intake.
Catch can from amazon $20/2 or 3 foot long 3/4 inch=19mm ID heater hose $20/ few hose clamps and attachments = 50 bucks and only takes 15 min to make and 5 min to install.
Cheap/quick way to rule out if PCV is for whatever reason dumping oil into intake or not.

garrett376

Great suggestion! I was going to come back to this thread this morning to suggest the above approach as well: isolate the PCV so you know where the oil is coming from. You can also undo the intake to examine the runners themselves and the intake ports to see if the oil is from the combustion chamber, or the PCV.

jpooley

I brought the first replacement PCV back to the first mechanic who checked it on his bench and said it was good. So I don't think the PCV itself is the culprit, but I'll still try the catch test!

Where else could it be coming from? I've read a fair bit about valve seals and symptoms of worn seals, thinking it might be them. However, was it just a coincidence that the seals suddenly went bad at the same time he replaced the PCV? Or could a properly functioning PCV create enough pressure to cause oil to be slipping past the valve seals now?

SMFCLAN

Just spit balling here ... in my experience replacing pcv usually raises crankcase pressure.... maybe look for some sort of blockage fore and aft of pcv....check for bore scoring at bottom of cylinders... piston rings worn....

jpooley

Mechanic said there was strangely NO pressure in the crankcase. I’m not sure how he tested that though…

How can I look for blockage? Would I have to remove the valve cover PCV unit to check?

jpooley

How much oil is a concerning amount in the catch?

mariusmight

So did you figure it out? We've got the very same problem...

jpooley

Sadly, we have not yet. Taking it to a 3rd mechanic tomorrow to see what they say.

As an update: I found oil in the air box again. The intake definitely has a lot of oil in it if it is enough to back flow through the throttle body and all the way into the air box…