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Oil Pressure Sender miscalibrated?


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SOLVED! Gauge error.

I know the oil issue has been hashed around a lot and I have read numerous posts. Given that my new (to me car) already needs a new transmission due to a bad PPI :censored: , I am now paranoid about everthing.

Car: 1999 996 C4 - 6 speed - new to me in the last couple of weeks.

Issue: Oil pressure gauge appears to read about 0.8 bars low.

Oil: Mobil 1 0W40 - changed last week. (I will likely go to a 5W50 next time)

Engine: Remanufactured 3.4L with a total of 25K miles on it.

Cold start up - 4.0 to 4.2 bars - never higher

Hot idle - 0.8 to 1.1 bars idling at about 600 rpm - engine showing ~190F (no evidence of warning light

Hot @ 3K rpm - 3.0 to 3.1 bar

Does this sound like the sender more than anything? Given that it appears to be consistently off....

Many thanks

Edited by fbgh2o
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  • 2 weeks later...

Key on engine off if you ground the signal wires at the sensor the gauge should sweep fully and illuminate the warning light. If not then the fault is within the gauge, maybe someone had the pointer off for whatever reason and now it's out of wack.

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All of the needles on my MY02 Targa "park" about 1/8" below the minimum values of the instrument when the ignition switch is off. When I switch the ignition switch on - before starting the engne - the needles indicate either zero (speedometer, tachometer, oil pressure) or actual static values (fuel quantity, voltmeter, coolant temperature - if above 100 degrees F).

If your oil pressure gauge actually does move from "about -0.4 bar" toward 0.0 bar....I agree with wvicary's thought that someone had earlier removed the oil pressure gauge needle - for some reason - and then replaced it without proper indexing. In that case you or an instrument shop can re-index the needle. However, if the needle doesn't move toward 0.0 bar, I suspect that you have a problem with the inner workings and hidden mechanisms of the oil pressure gauge itself.

Bill

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If your oil pressure gauge actually does move from "about -0.4 bar" toward 0.0 bar....I agree with wvicary's thought that someone had earlier removed the oil pressure gauge needle - for some reason - and then replaced it without proper indexing.

I am going to guess that this is correct, because:

  1. The PO did do a gauge face swap at some point.
  2. The needle parks at about -0.8 bar below 0 off and moves to -0.4 bar when the ignition is on but the car is not running.

Thanks for all the help!

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Sorry if I am hijacking this thread but I have the opposite....readings of 5 bar when cold and above 3 when fully warmed at idle moving to 4.7 at any RPM above 3000. I use Mobil1 0w40. I have replaced the sender. Does this seem ok? THanks

Your oil pressure is fine.

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I believe the reason for differences in grades of oil is primarily for people who start the car and take off. I believe in letting an engine warm up before applying revs to it. I've always done that with my gsxr1000 and plan to do it with my carrera. The gsxr does twice the revs and hp to weight ratio would be like a 1,500hp engine in the porshe. When the oil is cold it is thicker than hot so it will give higher preasures on the engine gaskets. Hawaii's Porsche dealership dictates 15w50 synthetic and I would be inclined to use the same in cold but always make sure the engine is warmed up before going into higher revs.

The manual states with a warmed up engine at 5k rpms you should be reading approx 3.5 on the preasure gauge.

I just had the dealer sheck out the car today and change the oil to the 15w50 synthetic and the once looking low preasures are looking great now. I had the same problem you refer to before I got what porsch's guys recommend. Go for the max protection. Funny thing is with synthetics if you have been running a blend or non synthetic oils you'll even end up with a higher rpm due to the extra smooth lubing the oil does. Seen it with bikes before when guys change over to synthetic and now after getting the previous owners choice out of the sump the car got a higher idle too.

post-51990-1260531548_thumb.jpg

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  • 1 month later...
I believe the reason for differences in grades of oil is primarily for people who start the car and take off. I believe in letting an engine warm up before applying revs to it. I've always done that with my gsxr1000 and plan to do it with my carrera. The gsxr does twice the revs and hp to weight ratio would be like a 1,500hp engine in the porshe. When the oil is cold it is thicker than hot so it will give higher preasures on the engine gaskets. Hawaii's Porsche dealership dictates 15w50 synthetic and I would be inclined to use the same in cold but always make sure the engine is warmed up before going into higher revs.

The manual states with a warmed up engine at 5k rpms you should be reading approx 3.5 on the preasure gauge.

I just had the dealer sheck out the car today and change the oil to the 15w50 synthetic and the once looking low preasures are looking great now. I had the same problem you refer to before I got what porsch's guys recommend. Go for the max protection. Funny thing is with synthetics if you have been running a blend or non synthetic oils you'll even end up with a higher rpm due to the extra smooth lubing the oil does. Seen it with bikes before when guys change over to synthetic and now after getting the previous owners choice out of the sump the car got a higher idle too.

FWIW:

I am using M1 15W50 and get a tad over 4 bar at revs over 3,500 rpm when engine fully warm (90-95C on the coolant readout) and 1.5 bar at idle.

I live in Houston where ambient temps rarely drop below 50F..

JP

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  • 3 months later...
Key on engine off if you ground the signal wires at the sensor the gauge should sweep fully and illuminate the warning light
.

Tested tonight... and got full sweep in the gauge. I guess it is time to test using an analog gauge to see if the gauge is miscalibrated.

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  • 3 weeks later...

After having tried everything else, it appears that the issue was the gauge in the cluster. I bought a used and installed it today. At start-up, the needle went straight to 5 bar (and the oil was probably still a bit warm). I am going to guess that the PO, when he changed the gauge faces, damaged something in the gauge and did not properly index it when reassembling.

I come out really ahead on this as the new cluster was a Canadian one, so now everything is in the correct units as well.

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  • 2 months later...

Key on engine off if you ground the signal wires at the sensor the gauge should sweep fully and illuminate the warning light. If not then the fault is within the gauge, maybe someone had the pointer off for whatever reason and now it's out of wack.

My oil pressure guage rest just below the '1' but will move a little lower and rise almost to '2' with the key in/engine off....so I'm wondering if a bad pressure sensor is the culprit to the 'low oil pressure light' I get.

To accomplish 'ground the singal wires at the sensor' can I just touch one of the leads to the body of the car, suspension, engine block?

I've been chasing a 'low oil pressure light' occuring at idle, and strangely, only in the afternoons.

No codes on the Durametric, even plugged in while light is illuminating and still nothing (meaning nothing on DME or instrument check). Throttle body, plenum, air distributors all cleaned when new hose that snakes from the AOS across the top of the block to the other side was replaced; replaced oil filler tube, clutch and RMS (no problems with IMS leaking) at this time too.

Mechanic checked AOS (which was replaced 8 months ago) and believes it is all fine, secured etc.

So I'm really hoping it is the sender.

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