Update on my oil consumption issue

2000 S, 188K chassis, 140K engine.

I posted a few weeks ago that my car was using oil after an oil change particularly after some hour long, fast highway runs. I then added a bit more than a quart of Mobil 1 15-50 heavy oil and guess what? Consumption stopped. I noticed this a long time ago that my car consumed oil back when they started putting in that 0W stuff.... and I would get spotting on my garage floor. With heavier stuff.... it stops. Go figure.......

difference in the engine's oil consumption.

BTW, the oil may not be going through the engine via the path you think it is taking anyway. The oil may be routed to the intake of the engine by a poorly operating (and maybe intermittently poorly operating) AOS which when it is particularly bad routes more oil vapor to the engine where it is burned.

And at the risk of starting yet another oil thread, I can't see running a non-approved oil to address an oil consumption issue that is only an issue because one is seeking 'zero' oil consumption which is nigh impossible to achieve. So many owners let some posts about how some cars use no oil make the owners of cars whose engines use a bit of oil look down on their otherwise perfectly fine engine because it happens to use a bit of oil.

If the oil consumption were high enough to be a concern, to the point the engine's behavior was being affected by the extremely heavy/excessive oil consumption, the proper way to address this would be to address the underlying cause of the heavy/excessive oil consumption, not risk the overall good health of the engine running some non-approved oil. Granted it is a small risk based on the number of owners who run this oil but still.

Sincerely,

MarcW.

When I got the car back, it consumed oil at a faster rate than it ever did before. Now after I added the heavy oil, maybe coincidental, it stopped. I have noticed, again maybe coincidental, that when I had 0W, I would get spotting on the floor and heavier stuff not. I am not worried about oil consumption per se, but I am concerned with variability. Consistancy is good, inconsistancy causes me to take notice. Overall the car runs really well and doesn't smoke at all. Look, I am not worried the engine is going to fall out or anything, but I like to fix stuff before it causes other problems or leaves me stuck someplace.

smoking upon startup and while sometimes this arises from the treatment the engine received during the previous trip -- not necessarily gruesome treatment maybe just a short trip -- often times the symptom appears out of the blue and after being subjected to the same conditions after which an engine start produced no signs of any smoking.

Because my usage of my Boxster is so consistent I'm always caught by surprise when the engine enits a cloud of smoke upon startup and after thinking about this off and on over time this I believe is due to the inconsistent performance of the AOS. If I'm right the device appears it can under perform its function just prior to engine shut off, which indicates to me it can under perform at any time the engine is running. This includes not only idling just before the engine is switched off but at any time during a trip.

Thus the AOS can allow an excessive amount of oil vapor to pass through it into the engine where the vapor is of course burned. The engine is up to temperature and unlikely the oil will create any smoke that you'd notice.

There is nothing special about my car and its AOS so I believe that if my theory is correct many cars are fitted with an under-performing AOS or the AOS starts out ok but degrades over time to the point that unless it fails outright it exists in a state in which it allows excessive amounts of oil vapor to pass through to the engine.

Just in case, though, one or two tricks is to whenever the sun is low at one's back to drive the car in such a way to try to see if the engine is emitting any oil smoke. What this involves is to run the speed up to whatever and then let off the throttle and allow the engine to slow the car on its closed throttle. This works to decrease the engine crankcase pressure and this works to pull oil into the valve stem/guide area, in the ring area (I mean there is oil already in these areas are you'd have in no time a very sick engine) but more oil if at all possible. The valve stem/guide seals and the rings work to keep this oil at a reasonable amount in those areas. Not enough oil is bad, very bad. Just right is good. And just right depends on various factors. But too much oil while not as bad as not enough is not good. But it can be tolerable.

Anyhow, at some point floor the throttle. Concurrently glance in the rear view mirror for any signs of oil smoke, or haze in the sunlight.

Or at night at a stop light with cars behind your's the engine idles some time. This also works to keep the crankcase pressure low. Then within reason use a lot of throttle upon take off from a stop. Concurrently check the rear view mirror to see if you leave any cloud of exhaust from this.

Every so often I do either of the above but the first technique is quite easy to do given my to/from work commute that has me driving west in the morning with of course the sun at my back and driving east in the evening (summer months anyhow) with the sun at my back. There is one downgrade (each direction) of several miles that I can under light traffic conditions coast nearly down the entire grade with the transmssion in high gear and my foot off the throttle. I have yet to see any oil smoke so the rings and piston and valve stems and guides and their seals I believe are still in pretty good shape.

In short before I blamed the engine for consuming oil -- provided it exhibited no signs of smoking after the above two 'tests' -- I'd blame the AOS.

For the oil leaks I do not know what to say other than I think I would prefer to if the oil leaks are not too bad to live with them. Or the oil leaks were too bad to live with to at least see if I could address them, lessen the amount of oil that is leaked, by more frequent oil/filter services (though I have to admit I'd really be at my threshold of 'pain' if in my case I thought I had to change the oil more often than every 5K miles), and perhaps switching to a different oil, but I do not think running a different oil would include running an oil not on Porsche's approved oil list.

But I have to always add that it is your car and of course you can run any oil you choose. Maybe it is just me, but I cringe just a bit when I read of someone -- with the best intentions of course -- running a non-approved oil sometimes for the flimiest of reasons, and in some cases a really sub-par oil. (I think of the 996 Turbo owners who have taken to running some diesel oil in their Turbo engines, an oil that has as a percentage of its make up mineral oil and this makes me sad...).

Anhow, if the oil leak failed to be brought under some reasonable control by the above, then I'd consider having the leak fixed by some mechanical means, which means replacing the bad seal or the bad gasket or spark plug tube o-ring or resealing the camshaft cover, adn so on.

Sincerely,

MarcW.

Generally, when your car emits an occasional smoke bomb upon startup it is due to the particular position of one of the pistons when the engine was shut off.
In that particular position of the pistons a drop or two of engine oil can pass by the oil ring gap an into the combustion chamber.
Remember these are flat engines where there is liquid oil behind the pistons, not so in other types of engines.
That's why it's a big cloud and why it's sporadic, because the engine won't stop in that same particular position too often.

When you start getting periodic and regular smoke bombs upon startup it is generally the sign of a bad Air Oil Separator.
The AOS acts like a reverse osmosis water filter. It has a diaphragm that filters oil droplets from the crankcase gasses.
It then distills the oil drops back into the crankcase and the somewhat clean gasses that pass through the diaphragm go to the air inlet system, behind the throttle body, to be mixed with the incoming air and burned with the fuel.

The AOS cannot act in an intermittent way. When the diaphragm tears, it's going to pass oil into the engine. If you let it go it can hydrolock the engine.

Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Quote
Pedro (Weston, FL)
Generally, when your car emits an occasional smoke bomb upon startup it is due to the particular position of one of the pistons when the engine was shut off.
In that particular position of the pistons a drop or two of engine oil can pass by the oil ring gap an into the combustion chamber.
Remember these are flat engines where there is liquid oil behind the pistons, not so in other types of engines.
That's why it's a big cloud and why it's sporadic, because the engine won't stop in that same particular position too often.

When you start getting periodic and regular smoke bombs upon startup it is generally the sign of a bad Air Oil Separator.
The AOS acts like a reverse osmosis water filter. It has a diaphragm that filters oil droplets from the crankcase gasses.
It then distills the oil drops back into the crankcase and the somewhat clean gasses that pass through the diaphragm go to the air inlet system, behind the throttle body, to be mixed with the incoming air and burned with the fuel.

The AOS cannot act in an intermittent way. When the diaphragm tears, it's going to pass oil into the engine. If you let it go it can hydrolock the engine.

Happy Boxstering,
Pedro

ring then the engine would smoke every time. There's at least one piston/cylinder positioned for this oil through this theoretical path to make into the engine.

While there is oil on the moving parts there's nothing to push the oil past the rings (there is the oil control ring, and two compression rings) and the very small gap between the ring and the piston groove and between the areas between the several rings between the close fit of the piston and the cylinder.

The AOS is the best candidate for not only the cause of intermittent smoking upon startup but for oil consumption.

The AOS from my Boxster -- I cut it apart -- has no filter of any kind present. The diaphragm is not porous and is there to control the amount of a valve which is used to control the amount of low pressure in the crankcase.

The pressure wants to be low, to lower the temp at which gas and water boil to help boil these out of the oil, but it doesn't want to be too low or it will result in well, worst case constant smoking as the engine's oil (at least in vapor/droplet form) is sucked out of the crankcase and at such an amount and speed the oil vapor/droplets do not get removed from the crankcase fumes.

The AOS has a nautilus shell shaped inner chamber with decreasing radius turns which causes the oil vapor to flow around/through the AOS in ever tighter circles. Plain old centrifugal force separates the oil vapor from the crankcase fumes that are routed through the AOS. The oil that is flung out of the crankcase fumes collects on the walls of the chamber and these are arranged so the oil can drain back into the crankcase.

Simply put the AOS sucks. And not in the way it was intended. Thus it not only accounts for the failure most of us have experienced at least once, which requires its replacement, but I believe accounts for some of the 'excessive' or 'intermittent' oil consumption that some owners report.

Sincerely,

MarcW.

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Perhaps combined with its occasional causative stopped position it allows sufficient oil to pass and get blown out on start-up.



Edited 1 time(s). Last edit at 04/02/2012 02:57PM by Laz. (view changes)

Well my last 4 cars have never ever had to have oil added in over 50k miles, 72k, miles, 58k miles (Boxster), 6k miles. Yes I do change oil at about a quarter the interval the mfgrs call for...or less. But all of them are operated in normal manner with a mix of high and low speeds and city and 250+ mile drives. I think that is pretty darn close to zero oil use.

I'd have thought that replacing one tenth of the total volume of the oil with a non-0 oil wouldn't change the flow characteristics that much or affect the seals that much ... sounds like Bruce has a leak.

I used to get spotting on the floor but haven't seen that for almost two years. I dunno..... I guess I should just consider this the charm of an older car.

Bruce - I have to agree that adding one quart of 15W oil won't make any difference out of almost 9 quarts. In fact, I'd kind of be worried about how different weights of oil would interact in the crankcase. Why don't you try an oil change and use a 5W oil instead of the 0W? IIRC, the 5W oil is authorized by the manual (mine, at least) and the change would at least would give you an answer whether 5W makes a difference. My indie mechanic always puts the 5W oil in my 08 Cayman and I have had zero oil consumption in the last 3 years. I can't say it's because he used the 5W oil, all I know is that I almost never get a morning puff of smoke and the oil gauge has never moved at all in the 5000 miles I drive it a year.

I agree with Mark. If you have oil consumption, it will not be affected by adding in a quart(or any higher number)of heavier oil. Remember, 0w is the weight on a cold start, and the viscosity changes, as needed, as the engine reaches temp.
Again, there is nothing wrong with moderate oil consumption on any engine. I have had many cars in the last 40 years, and I remember at least a couple of those that were really inconsistant in using oil, eg. dropping a quart between oil changes occasionally, but sometimes not for as much as a year for no obvious reason. And avoid all the so-called miracle additives, they are bogus.
Also, a couple family members have had 911's. If memory serves, all the air cooled cars used oil at a considerable rate compared to the modern Porsches.