Question about Oil Pressure and Voltage

The oil pressure gauge ranges from 0-5. Where should it be? I am just not sure how to read it. How about the volt meter for the battery?

Oil pressure is going to be function of oil temperature and engine speed. You should see a minimum of about 3.5 bar of pressure at 5,000 RPM on a fully warmed engine (this equates to about 10 PSI per 1,000 RPM and is a good rule of thumb). But if the oil is cold, you shouldn't be surprised to see 5 bar of pressure even at idle. According the the Owner's Manual (you have one of those, don't you?), the normal range for the voltage gauge is 12 to 16 volts, but it will generally indicate around 13 volts if everything is functioning correctly. If the gauge consistently shows less than 12 volts when the engine is running, something is wrong and you need to take a closer look at the battery, alternator, or other wiring.

thank you very much. I was a little worried as I saw the oil pressure flux between 3 - 5. Just wanted to make sure that everything was OK. I will make sure to keep a eye on everything. Thanks.

Pull out the OM, sit in the driver's seat, and flip through it page by page. That was one of the best things I got to do when I brought home my Porsche. I thought everyone did this. Come on man!

I've got a follow-up question. My oil pressure at idle when the car's completely warmed up is generally right around 1.2, and at about 1 if I've been driving with vigor. Just strikes me as a little bit low from what I've seen around the internet, though I bet there's a lot of "I just turned my car on for the first time in a week and my idle pressure is at 3 by the time I've gotten to the end of my street" floating around. So 1-1.2 bar at idle at operating temp, normal? Edit: Pressure goes a touch above 4 at 5000rpm, so that's normal.

Don't pay attention to the manual as it is not accurate. If, in fact, you only showed 3.5 bar on the gauge while cruising at 5,000 rpm, you have a problem. The needle should be at 5+ bar at that engine speed. You should also never run with a gauge pressure of less han 1.25 - 1.5 bar at warm idle. People running Mobil Water in their engine will often see too low a pressure, especially at idle.

I'm using the mobil 15w50 as it gets damn hot down where I am and never too cold. Any idea what could lead to that? Maybe an issue with the oil cooler and the oil's getting too hot?

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15W50 will produce the following pressure. This is REAL pressure measured with a mechanical gauge. The normal operation of the Porsche idiot gauge should be very close to reading this also when using 15W50. Big diviation from these readings may be due to a faulty sending unit and/or gauge or weak electrical supply. Cold idle and above: 5 bar Warm Idle: 1.5 bar Warm cruising above 3,000 rpm: 4+ bar

Not that 1999porsche911 likes to read this, as it is commonly seen on all the message boards that he hates Mobil 1 0W-40, but I believe 15W50 is not on the Porsche approved list. 5W-50 will give you better protection at cold startup, and is on the list...take it for what it's worth. Cold defined as 70F oil and block. And it will give you just as good protection at higher temps. I will not say that it is exactly the same as 15W-50, because usually, the smaller the range, the better the oil operates witin the design criteria for that weight oil. But you will see less start-up wear with a lower viscosity. That may or may not be important to you. Your pressure sound fine. My car with 0W-40 exhibits the exact same pressures & reactions. After a really spirited drive, it's about 1.2 at idle...normally 1.5. It just means that the oil is a bit hotter & thinner

Well when I parked the car tonight when I got home it was sitting at just ever so slightly under 1. So something's up I think, just don't know what. Either the pressure sender is off, though it hasn't exhibited any other signs of going out, or something's making my engine run too hot. Edit: Coolant temp is a-okay though, so I can't imagine that the engine is running hot enough to kill the oil pressure that much. Another Edit!: 15w50 was listed as an approved oil on a 2007 TSB I looked at.

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With all due respect to 1999Porsche911, I'd follow the factory documentation available, starting with your OM. You sure? The approved oil list dated 9/25/08 does not list M1 15-50, but does list 5-50. If your oil level is between the lower and upper marks, and you are using an approved oil, I don't mean to sound dismissive , but I think you are worrying unnecessarily. Of course it doesn't hurt to ask your dealer or take it in for a look.

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15W50 Mobil EXTENDED is a good oil and still has the appropriate zinc levels in it to protect your engine. Mobil Water does not. You will also find more and more dealers moving away from 0W40 to a better oil. BTW: Many 3.4 engines came from the factory with 15W50 oil. Porsche's "approved" list is a pay to play list and not a list of the best oils available.

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Well hell, I'd rather worry unnecessarily than not worry uh... necessarily. The car has otherwise been perfectly fine, but I'll give a call to the dealer and see what they have to say, and what oil they recommend for this climate.

The dealership here in Birmingham, AL uses and recommends Mobil 1 0w30. I don't think I'll be swinging my car around there any time soon. FYI - It's Tom Williams Porsche, the same dealership that left a Cayman S in a local mall's outside display area long enough for the rotors to rust over and the car to become covered in cobwebs. Edit: Top notch Indy in town with two Porsche Premier Master techs uses 0w40. Honestly though I'd just hope to find some 5w50 around here, I just don't see 40 weight being enough for Alabama summers.

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I'm curious as to why you'd overrule the suggestion of a "top notch" indy and two Porsche Premier Master techs? I'm pretty sure that their remarks would seal the deal at 0w40 for me and I'd never give it second thought.

Because they weren't vehement, they just said they use the 0w40 and that it's "fine". I figure with the temperature out here and the way I drive there's no good reason not to use a slightly heavier, and still Porsche approved, oil.

Ask the PDE folks what they put in the cars at Barber.

They said 5w30 at first and gave me quite a shock, but it was just a sales guy--they use 0w40 so I'd say it's good enough for me. I should really stop worrying so much but that's what the car does to me: Smiles on my face when I'm driving it, butterflies in my stomach when I'm not.

My 2002 C4 oil pressure tends to have two readings...2 when completely warmed up at idle and 4.5 to 5 all other times. I actually had my oil pressure sending unit replaced recently as it started to read low and irratic.