Stumped - oil level question

Hi, I haven't been on here in quite a while but I am stumped and looking for ideas. Last week I drove my 996.1 2001 C4 for the first time in several months. Anyway, I drove around for 10 minutes or so listening and feeling for anything amiss and all seemed totally normal. I then went to the gas station to top off. About the only time I check my oil is right after a fill up because the car has never consumed oil (at least not enough to warrant addition between oil changes). When I went to restart, the oil level gauge was flashing the bottom bar so below minimum. I checked the dipstick and it was reading below minimum as well, just about at the little dimple below the min/max section. The station is only about two miles from home so I went home and checked it again. Both the gauge and the dipstick read the same. I waited twenty minutes and checked again with the same results. I added about a half quart of oil and rechecked and the gauge was at minimum and the dipstick just above minimum. I went ahead and added the rest of the quart and both the gauge and dipstick were at the middle of the range. That is where I like to keep it. I thought all was well but it bothered me why I was down more than a quart. The car had never burned oil so I decided an AOS test was in order. Yesterday I connected my manometer before I started the car just to be sure it didn't peg the meter and all looked fine so I removed the manometer and took it for a sedate warm up. When I hooked the manometer back up I was getting readings of around 5.8. A little higher than I would like but still I didn't think the AOS was shot. Now for the confusion. I rechecked the oil to see if it lost any more oil but, instead, some oil magically appeared. The gauge now reads above max and the dipstick reads just above the top dimple. My guess would be a quarter to a half quart over-filled. I usually run with the oil level about mid way between min and max so it looks like my oil was full already and it is now somewhere around 0.2 quarts over-filled. So my question. Where was the oil? Any ideas?

It takes a while for the oil to come to temperature in our cars. Once the engine is at operating temp the oil is quite not there yet. Also, the heads in our engines are really good at keeping the oil in there and draining it rather slowly. Combine the two and it sounds like the oil never fully drained back to the sump making you think you were low. Even after a spirited drive where you go through a full heat cycle it can take upwards of an hour for oil to drain down and give you a better reading. General consensus seems to be to let the oil drain overnight and then check level. This is tough to do if you park overnight at a spot that is not perfectly level. Overfilling is not good and keeping it at half is what I do.

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Pipete84, Thanks. I thought about that idea for a while before I posted and again after reading your reply. My problem with that idea is that in all of my times checking oil in both of the 996s that I have owned was the gauge off by more than one or two bars after a fill-up. It was blinking the bottom bar. Since I run at halfway between min and max I run about .8 quarts below max or above min. To be blinking the bottom bar it means there was at least a quart missing somewhere in the engine. The engine was warm and after I checked it, I waited an additional twenty minutes, after the initial ten minute wait, to check again and there was no change. This has never happened before on this or my previous 996. I know they drain slowly but, to me, this drastic a difference implies that the oil was trapped somewhere. The reason I asked the question is the only plausible explanation I could come up with was a plugged oil passage somewhere that prevented the drain-back but I don't know where the engine has a passage that could block a whole quart of oil. When I rechecked after the AOS test, I only waited 10 minutes and it showed overfull so no problem with the oil slowly draining back that time. Since I always run about .8 quarts below max and after adding one quart it now reads overfull the oil was obviously there but that one time did not drain back normally.

Those are fair questions that I unfortunately may not have the answer to so maybe some other knowledgeable members might chime in. FWIW I did notice that the electronic oil gauge seems extremely sensitive to the car not being on a perfectly level surface to give you a true reading. By this I mean that I have seen reading anywhere from two bars from the bottom of the gauge to full depending where I parked. And I'm not talking about parking spaces that are clearly at an angle tilting the car. As silly as it may sound, I've decided to check the oil at the same spot every time if I want a proper reading eliminating the variable of the car not being perfectly level. Luckily there is a spot around the block where I can do this.

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Plpete84, Thanks again. There may not be a good answer it just really irritates me that I messed up something so fundamental. As to your observations and remedy on the level ground issue. I agree completely. Your solution is pretty much what I do as well. That is why I took the car home to double check it before doing anything. I use the same garage bay every time I check the oil. The gas station I was at is one that I use very often and it is pretty level but I still don't trust it 100%. If I'm somewhere with any discernable tilt, I don't even bother looking at the gauge.

When I first start the car in the morning, I wait a few seconds to read the oil level gauge. The gauge responds almost immediately. If I go to the gas station and fill up, the oil level countdown often says 47 minutes to achieve an oil level. Something about filling up throws that countdown timer all whacky. I just drive off because I know from early first start all is well.

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My guess here would be that the trip to the gas station is not long enough for you to bring the oil to anywhere near its operating temperature. As such the computer knows the oil will be thicker and require more time to flow down to the sump and in turn telling you it will take 47 minutes until it's able to provide anywhere near a true reading.

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DBJoe996, Are you sure the gas flap sensor is working correctly (try leaving the gas flap open and setting the alarm)? I've never seen that at a fill up but if I drive the car around for a while but then let it start to cool, when I do a restart I may get a wait time of 20-25 minutes. I'm wondering if it doesn't see the gas flap opened to trigger the oil level logic. I'm guessing that the way it knows you filled up is by seeing the gas flap opened and then closed again after some period of time. I did wait the whole 24 minutes once just to see what happens and it did read the level correctly.

After a fill up the countdown ranges anywhere from 10 minutes to close to an hour. The gas flap sensor works. It is just an anomaly of the oil level gauge. I used to drive to Miami/West Palm Beach and would do a fill up and then just check the dipstick. Quicker that way and more reassuring. Remember back in the days you would pull in for gas and the attendant would pull the dipstick and check the oil? I do.

Either your integrated oil level sender wasn�t reading correctly that day, or it was reporting correctly and too much oil hadn�t drained. Since you have a dipstick, that�s an easy test. I only check and trust my oil level (99 C2) when stone cold in a level garage after 8+ hours. I only trust cold. When I drive around, I can get a reading that�s 1/2 quart lower than stone cold, depending on how long the engine was running, temp, and other factors. Yes, it�s entirely possibly to have at least 1/2 quart floating around in the engine (heads mostly) that will reveal itself after sitting for a long time and cold/flat.

This is why you only check the oil once per day; in the morning on a flat/ level surface! People drive themselves nuts doing constant oil level checks.

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Mike and Jake, Thanks. I learned something from this. I have never checked my oil level cold. Instead I've always followed my manual for the dipstick reading so I always warm the engine and then check the level on the dipstick. I've never really trusted the gauge although it does seem pretty accurate when compared to the dipstick reading. I usually just read the gauge during a gas station stop and leave it at that. Neither of the 996s I have owned have ever consumed oil, unlike the 83 SC Cab I used to drive. The only reason any of this happened is because when I filled the fuel tank the oil level gauge was flashing at me telling me I was below minimum. Even then I took it home and checked it in my normal spot both on the gauge and dipstick multiple times before adding any oil. I added half a quart and waited a while then rechecked and it did what I would expect. The level went up from below minimum to slightly above minimum. I waited again and rechecked. It still read just above minimum so I added the other half quart to bring it to mid point between min/max on the dipstick. Since the idea that it was suddenly consuming oil bothered me, I thought about likely causes for several days. I have zero leaks that I could find and no drips in the garage. The only thing I could come up with was the AOS so I checked my coolant for any signs of problems and took a really good look at the oil on the dipstick (it was still reading at about mid point even after several days of sitting). Both seemed normal. I decided to run a pressure check on the crankcase before I drove it around just in case. I hooked up a manometer and did a quick start up test to make sure it was within range. Then I drove around for about thirty minutes to make sure everything was good and warm and reran the pressure check. It was still within range. I decided to double check the oil to see if it had lost any more oil but instead it now read over max, just above the dimple on the dipstick above the min/max area. I checked the gauge and it was pegged. All I could figure is that an oil passage got plugged and has now cleared. That's why I asked the question on the forum. Guess the consensus, including my own, is that I'm an idiot. Thanks again. From now on I'll forget the manual and just check before start up in the morning.

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In my “coming home” video for all my engine purchasers, I explain that the procedure outlined in the manual sucks, and should not be followed. I then explain that they should fold that page in the manual double, and tape it that way, so they can’t ever read it again. Different oils play with this a lot, as well as oil temperature the last time that the engine was operated. The biggest issue is if someone fires the engine up, drives it a few feet and parks the car. This would be like pulling the car out of the garage, parking it outside and then jumping in later and performing an oil check. The oil didn’t get hot, and therefore is like molasses sitting elsewhere in the engine. The oil is there, just not in the sump, so it can’t be measured. I have had someone do this, freak out, and add 3 quarts of oil to the engine when it didn’t need any oil at all. If you only check the oil on a level surface after the car hasn’t been ran for at least 8 hours (I prefer 12) then you can’t get an erroneous reading unless the sending unit is wonky. I consider the entire range of the electronic gauge to be the safe operating area. I urge people NOT to run the oil level at the very top of the gauge, since this makes it very easy to overfill the engine with oil. To me, the center of the electronic gauge is the “full point”. This also keeps the “hypersensitivity disorder” at bay a little bit for those who do crazy things trying to keep the oil level at the very tip top. One guy filled his oil using a graduated cylinder, and measured additional oil in MLs, he a spreadsheet and would fill it in every time he drove the car. About 3 months into his ownership experience with my engine he said that he needed a new AOS, even though we had just replaced it. The car was local, and we got it back for the job. When the car arrived I drained 3 quarts of extra oil from the engine. The AOS never failed, his hypersensitivity made him keep adding oil to the point that the engine had the symptoms of a failed AOS. After a nice scolding, he hasn’t had any more issues, and I had to go over the top to make sure that people don’t do this again. He is very lucky that the engine wasn’t damaged, it should have been. I have had an engine with only 1 additional quart added end up with damage. In your case something odd happened. The oil was in the engine, just wasn’t being measured, since it wasn’t in the sump. Heavier oils take more temperature to make it back to the sump in a timely manner. Some oils have a long more tendency to cling to the engine parts, no matter their viscosity and these also take longer. Driven GP-1 is one of those, and that’s why I like it, but the caveat is the oil level reading is more impacted by the “stickiness” of the oil.

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My countdown time does a similar thing. In the morning, cold, it's always some seconds. Throughout the day driving, it will sometimes show it will take hours to get a reading. I've just ignored it when it does this. Maybe I shouldn't.

It�s not really your fault. Checking the oil in this car is made out to be more complicated than it could be. I believe the difference between the very bottom of the dipstick and the very top is around 1.2 or 1.3 quarts. I only add 1/2-quart at a time because it�s possible these reading can vary by 1/2 quart.

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Jake, Your post should be a sticky somewhere on Rennlist. I never really thought about the part viscosity plays in the reading but I guess it is obvious. We tend to run slightly higher viscosity in Arizona. I run 5w-50. I know one shop recommends 15w-50. I've known that running the oil at mid point was a "best practice' for several years after seeing post after post of blown AOSs after a track day or even a spirited drive. They were almost always running oil at max whereas others that kept their oil mid point or so just didn't seem to have problems with the spirted drives or even track days (well, not AOS problems anyway--sure miss the old dry sump days). I'm going to do an oil change this week and see what comes out of the engine, hopefully just sludge and nothing important. Thanks again. Guess I'll cut myself a little slack and just come away a little wiser.

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Yep.. only add .5 qt at once when the indicator is at the last segment from the bottom, after 12 hours of sitting on a level surface. This puts the range right back to the middle of the safe operating range, and guarantees that you�ll never overfill the engine. These engines are the only in the history of the 911 series that don�t have their oil level checked without the engine running. Everything before them (dry sump) was checked with the engine running, only... Everything after them (9A1+) is also checked with the engine running. Checking the oil level with the M9X has always been a very misunderstood practice.