About a week and a half ago, I had the annual oil service done on the car - along with lowering it and adding a BMC filter - drove it around a bit, but today I took it out on the highway for an extended run and to make sure the springs were seating properly.

I came away from a light, put my foot into it and got the above message. Went back to the shop, and buddy told me that he has seen this on a few cars, let it cool down, then warm it up again - should go away.

I am inclined to give him the benefit of the doubt as I suspect the car is smart enough to be able to identify this problem the moment the oil was changed. What I am curious about is why a week later, and why under heavy load?

Is this the 'margin of error' within the oil level reading device, or is it something else I should be concerned about?

Cheers,

 

Oil starts to see the maximum coefficient of expansion at about the 215 degree level (assuming you are starting out at about 70). In our cars (capacity), that's easily 1/2 litre due to thermal expansion. You probably did not see the yellow caution warning last week, because the oil never got hot enough. The only warning you need to really worry about is the red one. You can drive on this warning, and in a couple/few weeks, it will most likely go away, as the car consumes a little oil. You are about 200-400mls overfilled.

If you keep the oil temp in the 200 range, you won't see the warning. But once the oil peaks up to about 215, you'll see the yellow caution pop.

 

For those that want to / like to see the math:



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


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)

where

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

where



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)

where

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

 

Interesting..I wonder why would Porsche not build this tolerance into the sensor software

 

Yup, makes perfect sense to me.

 

Nope, the car was overfilled, and you need to drain nearly 1 quart. The car does not even measure the oil until 200 degrees (you have to wait quite a while) and then it's measured. The owner's guide calls for the oil to ideally be BETWEEN the min and max levels, not at the max level. I'm afraid they forgot to unplug one of the three drains and then they filled all at once. Fortunately, this is not terribly concerning, but it is overfilled, and I expect you'd have a lot of smoke if you went on track.

Have the shop remove a little bit of oil and recheck until the measurement is between the lines. This is not "normal" at all. If you want to humor the shop, you can try what they said, but I give it a 9% chance of working. Please report back in a week how it went.

 

/\ it's not over by a quart. If it were, it would throw the red (do not drive) warning.

 

It's closer to a quart than half a quart...to get it to midway between the min and max. Just take it slowly and go in small increments until you get it right.

 

“9%” .......I love it.

 

Three drains?

 

Randy could certainly be right when he says nearly a quart full. Impossible to tell how over-filled it is since the digital readout is maxed. But you never want to run over hall full on the display or you'll soak your passenger side intercooler and intercooler pipe. And oil in the intake tract on a DFI car is not good because of it's inability to clean itself due to the lack of port injection.

 

Oil changes on the 991 are super easy. Drive one tire up a curb and drain a quart. It'll take 5 minutes tops. No undercarriage trays to remove

 

I can see why you have 21,000+ posts - thank you, appreciated.

 

I'll go out and have a look in a bit; and advise, but with all that, it would appear that it has to go back to the shop - unless I can siphon out .5/1.0 quarts through the filler tube...

 

No can do, Amigo.