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Oil OVERFILL warning (without reason)

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Curious if anyone here has any info or history with an intermittent warning message for oil being OVERFILLED.  2015 Cayenne S, 15K miles.  Oil was last changed June 2016 and meticulously brought up to the proper level over a short period of time.  Volume matched proper fill amounts as well, so no mistake on the amount added.  Never had any such messages until about now 2 months ago.  Intermittently will come on, stay illuminated perhaps for 1-2 drives, each in excess of 30 miles or more.  Then just as started, goes away without warning.  Absolutely no control or dynamic changes on vehicle, except for 2 rare items, also perhaps over same interval of time.  On rare occasion at a stop an irregular at idle under proper RPM, but no driving impairments.  Also on maybe 2-3 separate occasions, a backfiring sound with ignition (not hot or cold isolated), but no warning messages alerting with it--and none is consistent with oil overfill warning as well.  Just 3 separate diagnostic issues that don't always correlate with one another--but have evolved in this broad time frame of 2 months.  


Called one service place--to ask about setting up appt--was told it's from not driving the car long enough, and was told oil must be sloshing and dripping on areas that trigger the sensor.  I call BS on that--I'm not a soccer mom (nothing against it) driving the vehicle and enjoy DIY'ing the vehicle etc., and am very clued into the systems of it all.  Didn't even want to really have me come in.  Are you kidding me?  Moreover, after an additional 8000 miles since the proper oil fill, it is impossible there is more volume in that pan than 8 months ago.  Arguably a decent amount below the max fill given my enjoyment of utilizing the vehicle to full dynamic ability often when properly warmed up.  Oil should be being consumed in other words...


The service mgr told me it is a sensitive system and if filled nearly to the top it can do this.  


Does anyone know the failure mode of this alert exactly if it's not truly high?  Can anyone put together the other aspects (btw, which haven't really persisted but the oil alert is occurring nearly ever 3-4 drives now?

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I'd be inclined to go with the overfill warning. Who actually carried out the oil change?


I believe that synthetic oil 'expands' more than regular oil when hot. You could therefore have a level which is marginally below overfill when cold but which then tips into overfill when hot?


I'm fortunate enough to have a dipstick on my Boxster in addition to the dash indicator. If you have an extraction pump, I'd syphon a bit out. Alternatively, removing the oil filter housing drains approximately 1 litre. 


If that's possible on yours, I'd extract 0.5 litre and take it from there.





Edited by wizard
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I did the oil change myself, been doing it for years on all vehicles.

As is always done by me, the oil is underfilled a bit, confirmed by the multiple assessments on the sensor (which I know is not perfect), then properly added in small increments to bring the measurement up to the proper fill level.  

It was changed 8 months ago--and did not show these errors anywhere in an 8 month period, so I don't think the expansion suggestion makes sense in this case.  It should be happening ever since the change, rather than only recently.  

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You overfilled the oil back in June. Probably by about 200-400 mls. Not much, but, you're over.


Some Porsches burn oil. Some don't. Normal. Yours appears to not burn oil. That's good & normal.


Our oil levels CAN go UP with low usage due to combustion moisture building up from daily driving, on short trips. Oil never gets hot-hot. Can easliy be 5%. Almost a 1/2 quart.


Thermal expansion is a VERY REAL issue. I'll show you the match below. That can be another 1/2 quart.

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Here's the math I promised you:





Max expansion starts to happen above the 210-215 mark.

I remember seeing this equation this summer:

Specific volume of a unit can be expressed as

The change in the units volume when temperature change can be expressed as

dV = V0 β (t1 - t0) (2)

v = 1 / ρ = V / m (1)


v = specific volume (m3/kg)

ρ = density (kg/m3)

V = volume of unit (m3)

m = mass of unit (kg)

The density of a fluid when the temperature is changed can be expressed as


dV = V1 - V0 = change in volume (m3)

β = volumetric temperature expansion coefficient (m3/m3 oC)

t1 = final temperature (oC)

t0 = initial temperature (oC)

ρ1 = m / V0 (1 + β (t1 - t0))

= ρ0 / (1 + β (t1 - t0)) (3)


ρ1 = final density (kg/m3)

ρ0 = initial density (kg/m3)

Volumetric Temperature Coefficients - β - of some common Fluids •water : 0.000214 (1/oC),
•ethyl alcohol : 0.00109 (1/ oC), 0.00061 (1/oF)
•oil : 0.00070 (1/oC), 0.00039 (1/oF)

Hot engine ~220F and room temp ~75F and that's 145F temp difference. The oil volume expansion is then 0.00039 * 145 = 5.6%

5.6% of 9L of oil = 0.5L


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Hi and thanks for your detailed analysis.  But just to say again, that it never was overfilled in June 2016.  For 8 months, there was no overfill, and has not been triggered until the past 6-8 weeks.  How could it be overfilled then and not trigger a warning for 8 months (if it is that sensitive of a system), and now trigger an overfill if it is that sensitive of a system?  Then it wasn't functioning properly before if it was overfilled, and gave a false negative reading for 3/4 of one year.  Isn't that right?

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  • 11 months later...

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