Peter 642

Yes, another oil gauge question, but a quick one.
996 newb looking to buy a 2003 C4S; nice car.
At idle the oil pressure varied between about 3-4 bar.
No issues when driving; moved with rpms appropriately.

Something to worry about if I get that much wiggling while standing still?

Thanks.

ogun228

According to the manual, the oil pressure measurement is only to be taken after the engine has been brought to operating temp, shut down and left for about 5mins.
Not at idle.

Peter 642

Absolutely; curious if it means absolutely nothing that this varies at idle. I seem to remember reading that it's either nothing...or something substantial.

Macster

My limited experience with Porsche oil pressure gages (that of my 03 Turbo) is the needle can dance/bounce around a bit. At hot idle it can vary between say 2 bar to a bit under, but not even to 1.5 bar, maybe dipping to just 1.7 bar then jumping up to 2 bar. There is no pattern to the movement either.

At other times say when the oil (hot oil) pressure is 3 bar and of course the engine revs aren't too high and the car's being driven at a steady speed so the engine rpms are not varying much at all the needle can suddenly drop a bar if that much (and I don't recall ever seeing it drop more than 1 bar) then just as quickly bounce back up. Doesn't seem to happen if the oil pressure reading is much above 3 bar either.

If the oil pump was sick enough to vary its output that drastically in that short period of time I would not have been able to put over 47K miles on the car since I bought it June of 2009.

So, the gage is not 100% accurate, in my Turbo's case and I dare say your car's case as well. (Furthermore, I dare say the oil pressure gage is closer to an idiot light with a needle than it is a real gage, though not as near to one as the coolant temp 'gage'.)

Recently someone suggested the varying oil pressure was due to marginal electrical contacts at the oil pressure sender connector. The suggestion sounds plausible but I've never bothered to try to disconnect then reconnect the sensor connector to see if this improves the contact nor have I run this by my Porsche techs.

Now I did mention to my local Porsche techs the bouncing oil gage shortly after I bought the car but they said it was nothing to worry about. They have had several chances to change their minds since the car has been in there a couple of times for service. Also the car is still under (CPO) warranty so if the oil pressure was anything serious I'd bet there'd be some action taken. No dealer wants to forego billing Porsche for the cost of a Turbo engine R&R.

Oh, BTW, 3 to 4 bar at idle is high. Is that hot idle? What oil are you running?

At idle hot idle my Turbo's oil pressure is between 1.5 bar (actually it never gets quite to the 1.5 bar mark but stays maybe a needle's width above this mark) to 2.0 bar depending upon how 'hot' the engine is and this depends somewhat on how high the ambient temperature is. Sure there are radiator fans but the engine runs a bit warmer in hot weather and a bit cooler in cold weather. Also, it makes a difference how fresh the oil is. After an oil change the oil pressure's a bit higher at hot idle than it is again at a hot idle with 5K miles on the oil, which is when I change it.

Oh, you are about to buy the car. Then I would advise you to with the AC off start the engine cold making sure all the dash warning lights come when you turn the key to on then they all go out at engine start or very quickly after.

Let the engine idle and warm up and listen to it very carefully. If there is any oiling problem (like too little oil pressure) you'll here the engine get noisier as it warms up.

Let it get nearly to operating temp then have the seller take you on a 15 mile drive, vary the type of driving.

If you still like the car when you get back to the starting place, give the engine another close listen and then drive the car over the same route driving the car the same way.

If there's an oiling problem you'll know it.

Now be aware the seller may (I said may!) have dumped in thick oil so pay attention to the oil pressure at all engine speeds. If even hot the oil pressure stays 3 bar or higher... be suspicious unless you can tell me these 996 NA engines run 3 bar at hot idle even with Mobil 0w-40 oil.

If the check out goes well and so on then be sure to bring the oil level issue to the attention of the person giving the car a PPI on your behalf and get his opinion.

You might even stop in at the local Porsche dealer and mention that you're thinking of buying a used Porsche and of course you plan on relying upon this dealer for the car's servicing and other work should it be necessary and can you run the oil gage behavior by one of the senior techs for his opinion?

Sincerely,

Macster.

Peter 642

Thanks. Was thinking I may be wrong at number that high. Was a test drive and so I need to look again. Unsure what they've put in it, but there's a decent chance come tomorrow the car will be mine, and so as I now go looking for problems, wanted to know if I should focus on this one. Car was hot by the time I drove it, though.

Pac996

Not sure if Macster mentioned but if the oil isn't being picked up good then you can get surges. I got it in my younger years after letting the oil level drop too low. Then if the oil pick up or passage sucks air from cracks or seals leaking it would probably also do the surge trick of going up and down.
OR YOUR OIL IS BOILING

redridge

3-4 bars? Was the rpm steady at idle..... Oil pressure is proportional to rpm.... Sounds like a good cleaning of maf, tb, air filter, leaky vac....etc. Doesn't like a big deal. For sure get a ppi.

Quadcammer

think about what you've just said.

Oil pressure only exists when the engine is running.

You are thinking of the oil level gauge I'd say.

fbgh2o

Here are some observations from my car. I have crossed checked with a few others and this seems about normal for many people.

Key facts:

• 1999 C4 with 3.4L engine. Engine was replaced 25K miles ago (30 months) by previous owner with a factory remanufactured one
• Oil = Castrol 5W50 Synthetic
• Pressure Sender was replaced in January 2010

Here is what I see

• Cold start up - 4.9 bars
• Idle @ 180F - 1.1 to 1.3 bars (never any evidence of a warning light)
• 2800 rpm @ 180F - 3.5 to 3.7 bar (typical highway speed)
• 4500 rpm @ 180F - 4.3 bar

Peter 642

Thanks all. Purchased car. When hot at idle, is at or slightly above 2. Jumps to 3-4 when revved, as it's supposed to. Watching and listening, but I suspect this isn't an issue. The PPI was fine; asked mechanic to look carefully and he was not worried. I'm sure something will come up quite soon....