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Startup oil pressure delay

  • 2004
  • 911 Carrera
Mileage: 
95 000
Engine
Engine
Green Bay, 
Wisconsin

Until a month ago, my car had 4 bar pressure on the highway and a minimum of 2 bar at hot idle. Now, it takes 10 seconds to build oil pressure after starting and only creates 2.8 bar pressure max pressure and will not exceed 2.8 regardless of revs. It sits right there like it is limited. And 1 bar at hot idle. Also, at the +/- 10 second point after starting, the revs sometimes drop a couple hundred RPM exactly at the moment the pressure finally builds. Like it is "ingesting" something. Very concerning. So far, I've changed the sender, which made the gauge read more smoothly but didn't effect the pressure values displayed, replaced the spring and piston with the beveled one - no effect at all, inspected the sump and pickup screen - very clean, and I measured the pressure with a brand new mechanical gauge - it matched what the dashboard says exactly. Today I had a look inside the oil pump - I see light scratching on the lower left diameter (drivers side). I have pictures if someone wants to see this.  I also took the passenger side scavenge pump off - it looks perfectly clean, and rotates very smoothly. I have not done an oil analysis, but will do so now that I just changed the oil. I'm perplexed by this. The car runs great, does not use oil, gets 26 mpg on my long commute and 30 on a trip. The IMS has been changed twice, preemptively.  I bought the car 30k and 2 years ago. At that time it had perfect compression, low valve angle error, very low over-revs. I've run 5/40 LiquiMoly and Amsoil full syn. My magnetic plug had only a small amount of smudge on it. I really have a hard time believing this engine suddenly wore itself out. Why does it take 10 seconds when cold to create pressure at the sender? Why does it pull the revs down when the oil pressure suddenly builds? (It feels like the pump is not turning for 10 seconds then suddenly kicks in. I'm guessing that is impossible since the hex drive shaft is intact with only a few shiny edges and no appreciable wear. On a warm start it builds pressure immediately, but only to 2.8 bar.  Also, when cranking, I see the gauge build 0.2 or 0.3 pressure. This tells me there is oil in the passages between the pump and sender. Once it starts, the pressure reads zero for up to 10 seconds.  My second symptom is the pressure is 1 bar lower than last month in all conditions. Help!  Something very specific seems to have happened, and I can't figure out what it is.  

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