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Hot!Constantly fluctuating oil gauge

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skyhighsi
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2022/06/15 06:28:56 (permalink)

Constantly fluctuating oil gauge

I have had my manual, UK 997.2 for 4 years now and whilst I never paid huge attention to the oil pressure gauge, my memory is that it generally sat at around 1.9 when driving steadily and increased to over 2 depending on speed and acceleration.
Having just had it serviced in the Netherlands for the 1st time since moving here, I now notice that the gauge is sitting at 1.4 and constantly adjusting between 1.4 and 3, even on very gentle drives. 
The new oil is Mobil 0W40 which is what the UK garages used...a different viscosity would answer the difference in behaviour but it's not that.
Has anybody got any ideas or views on what may be the cause to this change?
The only other change to note since this service is that the engine seems to be making a rough noise on the passenger side when idling.
 
I'm not overly concerned as the car runs well, I'm just intrigued. The car is going back to the garage to check these things but having some ideas may be helpful for me.
 
Thanks
post edited by skyhighsi - 2022/06/15 06:30:08

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jmaddox
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Re: Constantly fluctuating oil gauge 2022/06/15 14:18:27 (permalink)
Make absolutely sure they put in the right oil. Also with the ignition on before the engine is started is the oil pressure at zero. If the sensor is playing up it will not be at zero but reading 1 0r 2 bar or even maximum deflection. 

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skyhighsi
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Re: Constantly fluctuating oil gauge 2022/06/15 14:27:36 (permalink)
Will check jmaddox, thanks.
Are you suggesting it's not normal for the needle to fluctuate then?
The oil has been verified as 0w40 unless there was a mistake that no one is aware of at the garage but there are only 2 of them.
jmaddox
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Re: Constantly fluctuating oil gauge 2022/06/15 14:39:01 (permalink)
The gauge will fluctuate as revs rise and fall and that is normal on a fully warm engine. At its lowest on hot tickover rising to nearer full deflection at high revs.

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skyhighsi
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Re: Constantly fluctuating oil gauge 2022/06/15 15:37:32 (permalink)
I can clarify that the gauge sits a 0 when the ignition is on....so that's a good start.
jmaddox
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Re: Constantly fluctuating oil gauge 2022/06/15 16:01:58 (permalink)
Agreed. Your sensor looks ok then. I don't think you have anything to worry about. Just keep an eye on the gauge to ensure it is low at hot idle and increases as revs rise. 

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tscaptain
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Re: Constantly fluctuating oil gauge 2022/06/15 16:40:32 (permalink)
On the Gen 2 cars there is an on demand electric oil pump, unlike the earlier cars which have a mechanical pump.  The oil pressure on these cars is not simply a function of engine revs.  If you boot it from low revs the oil pressure will increase immediately.  Try it.  Your fluctuations sound normal to me.
 
PS  - always a good idea to pay attention to the oil pressure gauge
post edited by tscaptain - 2022/06/15 22:10:42

I'm speeding because I have to get there before I forget where I'm going.
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skyhighsi
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Re: Constantly fluctuating oil gauge 2022/06/15 16:55:18 (permalink)
Thanks guys.
Enough attention was paid to know it generally sat around 1.9 but now I notice a 'change' in behaviour, I question what I thought I was reading. Any change in behaviour after 4 years is always worrying, even if it is still within normal parameters.
 
Maybe the car is just excited to be nearer it's homeland?
Motorhead
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Re: Constantly fluctuating oil gauge 2022/06/16 10:50:09 (permalink)
Simon,
 
Just to clarify Alan’s point, the on-demand oil supply pump is a mechanical not an electric device and is DME controlled. In addition, there are four mechanical scavenge pumps drawing oil from the cam boxes.
 
As far as I can recall it’s a spur gear pump with the input shaft being engine-driven, the secondary shaft being allowed to move axially under solenoid control (via the DME) thus allowing variable meshing of the gears and varying the flow from the pump. Note that being an on-demand pump the supply isn’t necessarily dependent solely upon engine revs so revving the engine when the car is stationary won’t necessarily correspond to a proportional increase in oil pressure; it’s only when the engine is under load that you’ll see an increase in the pressure.
 
Regarding your issue, I suppose it’s possible that the pump solenoid is malfunctioning or maybe there’s an issue with its control, and it would be useful if your garage could run some Porsche-specific diagnostics (PIWIS or equivalent) to see if there are any associated error codes.
 
Jeff

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tscaptain
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Re: Constantly fluctuating oil gauge 2022/06/17 07:55:46 (permalink)
Yes, sorry, should have been clearer. To quote Porsche
 
"Four oil pumps remove the oil from the cylinder heads directly into the oil sump. A fifth pump in the oil sump directly supplies the lubricating points in the engine.
To reduce power losses and increase efficiency, an electronically controlled oil pump supplies the lubricating points inside the engine as and when required. This means that the oil pump does not work so hard when there is less demand for lubrication. The benefits of an on-demand oil supply system are optimum efficiency, reduced fuel consumption and lower exhaust emissions."

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Gen 2 997 turbo Guards Red/black PDK
SWMBO 997 GTS Platinum silver
Following: @PCGB_997

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