DASC4S

I've had my 02 C4s for about a month now. I've put 1000 miles on it, it is my daily driver. Best commute I've ever had, no matter what the traffic.

The other day I actually waited for the computer oil diagnostic to run. It reported me as actually below low. So i checked the dipstick and that looked to be the case. I put a quart of mobil1 0W-40 in. Didn't notice anything unusual in and around the filler tube. Drove 10 miles and ran the diagnostic again. Still below low. Added another quart. Still below low. Added another quart and then it was 1 bar above low. Added another and it was at full. I actually was doing this in half quart increments (per my manual) until I got impatient with it still being below low.

I drove the car for several days since then. It is driving great, sounds great. I have no white smioke at start up (only have had that and a little white goo in the tube when I haven't driven it much and run the engine for short durations so it never warms up - which is just when I need to move it around the driveway). The oil pressure when I first reached full on the oil (stupidly I never confirmed this level with the dipstick) was more or less pegged at 5bar if I was doing anything other than idling. Now a few days later is more like 2 bar at idle and going up to 3-5 bar depending on the rpms. I checked the oil. The dipstick and diagnostic both seem to confirm that I am at low again. I have no oil leaks that I can see. There is no smoke ever that I can see. My driver side tailpipe is sooty (black).

So is it possible to burn almost 4 quarts of oil in a week (over ~300 miles of driving at local to highway speeds) and not see big clouds of smoke? Is something else going on? I get the tailpipe points to oil being burned in the engine, but this seems alot. What I'm doing and going to do:
1) I've wiped tailpipe clean to see how quickly it soots up again
2) Remove the filler cap at idle and check for a vacuum pull to see if this is an AOS related problem
3) inquired locally about voodoo

Other suggestions? Should I try bumping up to 5W oil from 0W?

Thanks.

UPDATE 6-18-2017
1) I added 1.5 quarts of Mobil 1 0W-40. This morning at a cold start, later fully warmed up after filling up with gas, and 6 hours after last driving it the dipstick and electronic meter both read full. Car continues to drive well and sounds good as far as I can tell.
2) I did a cursory check on the AOS by removing the oil fill cap. I don't yet have any type of manometer. With the engine fully warmed up and at idle, the cap came off without much effort. There was definitely a vacuum. Covering it with my hand or not did not alter the idle at all. With the engine sitting for 6 hours and then starting it and repeating this test there was about the same vacuum (simply qualitatively determined by how much I felt pulling on my hand, so not quantitatively) but with my hand off the filler tube so it was open the idle got rough. Not to the point it stalled but definitely changed. The coolant tank is roughly just under full, as it has been since the indy shop topped it off 3 weeks ago during an inspection. Still the only smoke I see is when starting a cold engine after it was last run and shut down cold (as in I ran it to move it around the driveway). There is no noticeable smoke during driving or starting the engine while warm or if it was last shut down warm after a drive. In parallel to tracking my oil consumption I'm going to build/buy a manometer to quantify the vacuum. Since the AOS seems to fail at a high rate and is somewhat time consuming to replace it seems helpful to measure this.

Is any change in idle indicative of an AOS failure?

Next steps this week:
a) Will continue to monitor gas mileage, oil consumption vs mileage, coolant level, and amount of soot on tailpipes (I wiped these clean to provide a baseline) over the next 2-3 weeks.
b) I expect to be able to change both the oil and filter later this week. At this point I'll also install the the magnetic oil plug I ordered.
c) Build/buy a manometer and quantify the vacuum pressure.

Atrox

These cars go through oil, but 4qts is beyond excessive. If I were you I would do an oil change and start over. Try to measure the oil that comes out. Give you a blank slate to start from.

DBJoe996

Good idea on voodoo! Now for the issue. You are doing the right thing. You need to establish a baseline for oil consumption versus mileage. Remember the sump/engine contains about 10 QT's of oil. Check your oil level on the dipstick when the engine is stone cold, meaning, like in the morning before you fire it up. Then do this consistently for several days. Fill it back up to full if it drops and note your mileage. That should give you some good baseline data for oil consumption versus mileage.

Depending on the weather temps where you are, going to a 5W could help. You do not want to even begin to think about why the engine consumes to much oil - scored bores, piston rings, valve stems and seats, and so on. What you want to do right now is see how much oil is consumed and whether that is within a tolerable range.

Also note that I said to use the dipstick. The oil level guage is not that accurate, readings can vary depending on a lot of different factors. Use the dipstick for accuracy.

The oil pressure sounds about right, however, the oil pressure sender unit in our cars are notorious for erroneous readings, especially when old. Might consider replacing it.

Turbojamie

So rather than waiting the 10 seconds for the oil level monitor to report you simply ignored it for x amount of time and it was a full 4 low? Kind of irresponsible if you ask me. Hopefully nothing was damaged by the excessively low oil level. The engine will consume "some" oil but they are all over the place as far as how much. For instance my 03 C4S would use 1/2 quart in 5,000 km of driving at the most.

wildbilly32

Do you know, really know, if you started with a full charge of oil? I think each mark on the digital gauge is something like 6.7 oz. so down one bar is not tragic. I swear I read in the owners manual that 1 quart in 600 miles or 1000km can be considered normal, but I can't find it right now. I agree 4 quarts would be excessive. Recommendation on checking oil is stone cold as mentioned above, 24 hours if possible. Trust the stick and make sure it is fully seated against stop when doing measurement. I've caught myself not fully seating stick and come up with short readings. Just make sure...

Gonzo911

Check your coolant tank to make sure it's not going in there...

dporto

Also make sure you're on a level surface when checking the electronic gauge - it's very susceptible to false readings. The car has to sit for twenty minutes or so when warm to get any sort of reading - and it will still read somewhat low (it takes awhile for the oil to drain out of the heads and back to the sump). Accurate readings are taken after an overnight sit - and once again, on a level surface. Good luck

shawn_nj

I cannot get consistent measurements from the computer at all. Even taken same in the same level spot, warm engine and same timed since shutdown. Up and own swings of 4 to 5 squares, no consistency. I have given up looking at the computer completely and just use dipstick on a warm engine. I am burning a QT per 2000miles. I would not add oil based on computer alone. Make sure dipstick agrees if something doesnt seem right. Mine is 02 C2.

Macster

In your case it reads like the oil level sensor is broken. This sensor consists of a loop of wire the loop runs down inside a small diameter plastic tube that extends down into the oil sump. The loop of wire is bare. To take a measurement a known amount of voltage is run through the wire for a fixed amount of time and the voltage level that makes it through the wire is measured and this correlates of where the level is. The voltage level is affected by how much of the bare wire is submerged in the oil.

If the little plastic hook that holds the wire at the bottom of the plastic tube fails the loop of wire can move about and because it is not kept in proper position the reading will vary.

ejdoherty911

The computer on mine is rarely accurate. I use the dipstick. It's F-ING INSANE that new Porsches do not have oil dipsticks because their sensor systems don't work.

Macster

It is possible to burn 4 quarts of oil in ~300 miles but I would have to believe you would notice the engine smoking. Occassionally I observe a vehicle taking off from a stop light, or just going down the road/freeway and oil smoke trailing behind the vehicle. While it is clear the engine is burning oil I strongly suspect it is not burning 4 quarts in 300 miles.

Right now you do not know for sure just how much oil is in the engine.

My recommendation would be to have the engine oil properly drained and refilled with a known and correct quantity of oil appropriate for your car and at this time the tech would then check the electronic oil level sensor and system is working properly. Ask him to confirm the oil dipstick also reads correctly.

You want to know the engine has the right amount of oil and that both the electronic and dipstick measurement systems are reporting oil levels that are in agreement with each other and just as important in agreement with how much oil is actually in the engine.

Then drive the car as you normally do and keep track of the oil level.

Be very consistent in when and how you check this. The car wants to be very level. A bit up or down at either end can affect my Boxster's oil level reading by 2 bars. With the car tilted sideways the level varies even more.

I check my Boxster's oil both dead cold -- with the car having sat overnight unused -- and fully up to temperature. Often this oil level check is made when I stop and fill up the gas tank. The engine is hot, fully warmed up, and the gas station drive is quite level. After filling the tank the oil level reading count down starts at 5 seconds.

Check the oil level and monitor the change in the level. If you see the level dropping as you add miles then there's something going on. There's not much you can do on your driveway. I'd not bother trying a different oil. Really if the engine is using oil at the rate you suspect (but which I doubt is actually occurring) no oil will help and you don't want to run the wrong oil and possibly damange the engine internals when the heavy oil consumption might not be that serious of a problem, though obviously its cause should be found and fixed ASAP.

If you see the level varying -- this is assuming you use the electronic oil level system -- then what is probably going on is the electronic oil level sensor has suffered a problem (a loop of wire is loose and moves about and this affects oil level reading) -- and this needs to be addressed. Probably by having the oil level sensor replaced.

shawn_nj

Ironically I brought it to my INDY to checkout and ofcourse it works perfect infront of them. I have tried taking readings in a few different places (gas stations, most level places I can find) and it if I take enough readings it will show inconsistent results. It seems to work more than it doesn't...but overall I do not trust it. I just check the stick every week, before a cold morning start and up to temp. Unlike computer I have found the stick to be perfectly consistent....lol

Ahsai

Drive the car hot and leave the car parked overnight and check the stick before firing the engine in the morning. This is the proper way to get a consistent and accurate reading, period.

Mike Murphy

This is really important. Just because the car looks level doesn't mean it is. I wait the 5 seconds after a hot shutdown or restart and let the oil level check itself, and I get different readings all the time at various places...

Find a good known-level spot and park your car there after a good hot day of driving and check the oil the next day when cold. This is your baseline.

Chris(MA)

I hope this isn't a sign of something much worse...