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Thread: oil pressure?

  1. #1

    oil pressure?

    After changing to Mobil1 in my 2.4S motor, my oil pressure has increased by 0.5 on the pressure gauge (0 - 10 scale). At 3200 revs the gauge reads 4 exactly.

    Is it normal when flooring it (from 4000 revs up) the oil pressure needle shoots up to the top (10)?

    I'm assuming if there was too much pressure I would know about due to leaks etc..?
    1973 2.4S
    1993 964 C2
    987 Boxster Spyder

    'hot66'
    www.ddk-online.com

  2. #2

    Question

    Excuse my ignorance if it shows but I've never seen a 1-10 scale. Ive seen scales to 140psi and also scales in Druck pressure on later cars like SC's and Carreras.
    A cold engine could easily pop 100 psi. Anyone remember the rule of thumb for pressure/1000 rpm's?

    Tom
    "Be who you are and say what you feel because those who mind don't matter and those who matter don't mind." - Dr. Seuss
    "Experience is the mother of wisdom" - idiom
    "Let them that don't want none, have memories of not gettin' any"- Brother Dave Gardner

    Early S Registry #235
    rgruppe #111

  3. #3
    this is a 'Druck' pressure gauge

    without concentrating too much on the actual values, I was wondering if it was 'normal' for the pressure to shoot right up when under flat out accleeration?
    1973 2.4S
    1993 964 C2
    987 Boxster Spyder

    'hot66'
    www.ddk-online.com

  4. #4

    oil pressure ?

    James
    What you are seeing is normal for a cold (ie less than 180F oil temp).
    The 911 dry sump system uses a two part pump; one side to scavenge the oil out of the sump and send it back to the tank and the other side (pressure side) to pressurize the oil galleries of the engine. Unlike most automotive engines the pressure side is actually a constant volume pump rather than a constant pressure pump. This allows for wild swings in oil pressure from just a few psi at idle on a hot or somewhat worn engine to 100+ psi when an engine is reved. As a rule 10psi/1000 rpm is acceptable minimum; anything less and you may have excessive wear in the rod bearings.
    As for your guage reading 1-10. I recall seeing this type of gauge before and beleive that it was in atmospheres. Meaning that 1(bar)=14.7psi. Hence 10(bar)= 147.5psi.
    I have to admit that unless the numbers you gave are for a cold engine it is unusual to peg the oil pressure guage when reving to 4000rpm. Most folks are a lot more worried about the opposite problem. Hope that helps.

    scott
    scott
    73S
    73E

  5. #5
    thanks for the reply. The pressure / revs relationship is correct under normal driving.

    The high pressure reading only slightly worried me, but I admit it was cold day & i had only driven about 7 miles so the engine was not fully warm. Not having been out in the car for 2 months I think I was just being paranoid, watching all my dials & listening to every noise
    1973 2.4S
    1993 964 C2
    987 Boxster Spyder

    'hot66'
    www.ddk-online.com

  6. #6

    Normal Oil Pressure Reading

    Both my engines are very recent rebuilds, and at normal operating temps (i.e. 180-210) they register 60psi @ 4000 rpms. At higher rpms they will move upward, but I was not aware that there is a specific ratio of oil pressure to engine rpms?

  7. #7
    Originally posted by james
    thanks for the reply. The pressure / revs relationship is correct under normal driving.

    The high pressure reading only slightly worried me, but I admit it was cold day & i had only driven about 7 miles so the engine was not fully warm. Not having been out in the car for 2 months I think I was just being paranoid, watching all my dials & listening to every noise
    EEEK! Try to keep the revs under 3500 until the temp is around 180, okay? Then if it still shoots to 100 at 4,000? It may be time to change the sending unit.
    Paul D. Early S Registry #8 - Cyclops Minister of West Coast Affairs
    "Now, to put a water-cooled engine in the rear and to have the radiator in the front, that's not very intelligent." -Ferry Porsche (PANO, Oct. 1973)

  8. #8
    Paul is correct:

    You can do a lot of damage to a cold engine. It is always a good idea to let it get up to operating temperature before a flogging.
    My M Roadster gets water temperature in about 2 miles of driving, however, it does not get oil temperature approaching the magic 180-200 degrees for a good 10-15 minutes. Only then will I pull the trigger.
    Digressing a bit, Harley Davidsonís have for years had a problem with base gaskets weeping. (they are much better these days from what I hear) The trick was to let the bike warm good before spanking the throttle but most clowns jump on them, crank them up and let the big dog eat. Lots of leaks and worse yet, a ton of premature wear. My bike machinist who is an old hand with BMW's and Harley's says you cannot believe what some ass-***es can do to a perfectly good engine. Of course it's more business for him but he does have sympathy for the machinery.
    Go to Daytona Bike Week one time and I promise you will see some of *the* most asinine behavior imaginable.


    Tom
    "Be who you are and say what you feel because those who mind don't matter and those who matter don't mind." - Dr. Seuss
    "Experience is the mother of wisdom" - idiom
    "Let them that don't want none, have memories of not gettin' any"- Brother Dave Gardner

    Early S Registry #235
    rgruppe #111

  9. #9

    remember too...

    that each of the diffent types of metals that make up our engines have very different expansion/contraction temperatures. So each have unique warm up times and optimal operating temps. You want all of them to be near their optimal expansion (limit) before you "...let the big dog eat."

    Nice quote sithot.

    HD rocker cover gasket destroyer, Shawn.
    67 coupe roller
    99 M96 2.5 litre
    early911s reg 447
    R Gruppe 399

  10. #10
    Senior Member
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    1,012
    Originally posted by sithot
    Excuse my ignorance if it shows but I've never seen a 1-10 scale. Ive seen scales to 140psi and also scales in Druck pressure on later cars like SC's and Carreras.
    A cold engine could easily pop 100 psi. Anyone remember the rule of thumb for pressure/1000 rpm's?

    Tom
    Fully warmed up, it is usually 10-15 psi/1000 rpm.
    Harry

    Member #789
    1970 VW Sunroof Kombi Bus - "The Magic Bus"
    1973.5 911T Targa for fun - "Smokey"
    2009 MB C300

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