jim010

We have a 1999 996 C4 tiptronic. AOS has been replaced last year.

Just noticed a few days ago while driving in congested traffic, the temp gauge reading was reaching to 90 Celsius. At idle, the oil pressure guage was as low as 0.5 Bar. Oil in the car is 0-W-40 and the oil change was done by Porsche, and the temperature outside was 20 Celsius. Wife reported that she felt at idle there was a moment the car felt like it wanted to stall, but was idling at 500 ish.

I checked it out today. Temp is 15 Celsius. Idle was 850 ish rpm. Pressure started at 5 Bar as usual. Drove around and all seemed fine, as the pressure settled to 2 - 3 and 1 Bar at idle. As car got hotter and it climbed to 90 Celsius, oil pressure dipped to below 1 Bar, even to half. Oil light flashed for a split second, but did not hear any knock or anything. Turned on the A/C to get the fans going, in case it was that. and temp dropped and oil pressure went back to 1 Bar. Concerned, as it is not hot out right now.

Before I get the comment "do a search" I have. This is what I have found:

get the actual pressure tested to make sure the gauge is accurate. I will, but wonder as at low idle and low oil pressure, there was knock, although momentary?
Could be the sensor is out - cheap to replace
The pressure relief spring that broke in half for the sending unit
If the fans, get the low temp thermostat. Have a new one in there right now that is OEM installed by Porsche when they did the AOS.
Go to a heavier oil.

or finally, engine is about to blow up and run away...

The threads I was looking at wereod, so any new ideas would be nice. Car is parked until we get it looked at or we solve it ourselves.

Thinking of installing a manual switch to turn on the fans front and back, if that is the issue. But 90 Celsius still seems withing normal ...

Mike Murphy

My car pegs 5 or above 5 when cold, so if you are already just below 5 at cold start, you are going to be down 1/2-point tI begins with. The gauge could be off, or the sender could be off.

If you are idling at 500, that’s the cause of the problem. Idle should be a minim or 650 or 675, I cannot remember which. With the AC button depressed, I think it will run at 750-800 RPM.

You need to have the oil pressure tested by a real gauge. You may need to replace the filter bypass and oil pump bypass springs and valves. Inspect and make sure you have the proper filter. You may need to drop the sump plate and inspect the oil pickup screen to see if it’s clogged. Heavier oil will not fix any issue, but would be good as a last resort. You’ll only gain 1/4 point, but could make a blockage worse with heavier oil.

jim010

Correction, she says it is 5 Bar or more at start up when cold.

wyovino

Check out this thread.
https://www.renntech.org/topic/39205...essure-solved/

cds72911

Do some direct observation rather than listening to the customer (wife) "facts" and observations. My customers (wife and kids) are not the greatest at reporing useful diagnostic information. Also, I find it worthwhile to systematically troubleshoot issues rather than guessing and throwing parts at problems. Personally, I'd start with diagnostics on the guage/sender side, verify that that is good, then move on to the pumping and pressure regulation side.

As much of a car nut as I am (and I consider myself pretty mechanically inclined) I thought my oil pressure guage was wacky too, and I even went as far as buying a new sender before going back to basics and doing more observation to see that the needle did fluctuate properly. It just spends a lot of its life north of 4 bar in normal rpm range usage.

jim010

I read that one, yes. I included the spring as a possible culprit. Haven't checked the actual pressure yet, but will on Tuesday. Seems most likely to me as well.

After that, I am thinking of going to 5 W 40 and replacing the spring. Beyond that, it will have to be Porsche .

I haven't experienced the 'feels like stalling' at idle for myself, but i have seen the low oil pressure briefly flash at 0.5 Bar and idle around 500 woth temperature around 90 Celsius.

Imo000

If the idle is too low so will be the oil pressure. They go hand in hand. I would look into why the idle is so low that the engine is almost stalling before concentrating on the oil pressure.

Azraely

Jim,

I started a thread 2 years ago detailing the same symptoms you have. I also have a 99 with tiptronic located in Edmonton and I've experienced the same less than 1 bar of pressure. Worse at idle in spring/summer traffic. In winter, in stop and go traffic my idle is 0.8 or 0.9 Bar and my car idles consistently at 700rpm which I believe is what the engine hood sticker states for a tiptronic

Things I checked/did:

• Changed Relief Spring/Piston (Twice) (No change)
• Dropped sump plate looking for clogged pickup tubes, found nothing
• Took off swirl pots checking for debris, found nothing
• Changed Waterpump, Thermostat, new Coolant (This helped, but only really through lowering temps)
• Visual Inspection of the oil pump gears and housing while doing the water pump job, I didn't notice any damage
• Installed a manual fan switch for the front radiators to turn on high speed circuit (Helps, again by lowering temps)

Basically I've found nothing wrong that is correctable, I sort of resigned myself to either it wasn't a problem or its a problem related to the main bearings or something else involving a complete teardown to find out. I've since driven 15,000 km over 2 years and nothing has changed. Hasn't gotten better or worse.

I do switch to Mobil 1 5/50 in the summer and that brings up the pressure somewhat, but it still does not idle above 1 bar when warmed up in moderate stop and go traffic. Somewhere in a Porsche manual it's stated that if you have 3.5 bar at 5k rpm that is acceptable. My car produces 4bar at 5k RPM even after sitting in 30C stop and go traffic and is idling somewhere around 0.6 or 0.7bar.

docmirror

and now for something completely different.

1. Clean rads and condensers.
2. Install 160F low temp thermo(I can't tell from your statement if you have, or don't have it already)
3. Use correct oil viscosity for your car(5-40)

It appears your issue is thermal related.

YMMV, objects in mirrors, contents have settled, and may cause **** leakage

jim010

Rads I cleaned last month. No debris in there anymore. I fully intend to change to 5 W 40 asap. As for the low temp thermostat, I may, but am thinking of installing a switch to turn them on when I want.

jim010

Azraelly, we should meet! Compare notes.

Imo000

Before you install a manual switch..........is there really a problem that you need to fix or you just think there is a problem? To me, it sounds like you are looking for a solution for a problem that doesn't exists. Is you idle too low?

jim010

Today idle was at just over 600 when fully warm. Couple times when at a stop light, it dipped to below 600 momentarily. Did read below 1 Bar and as low as 0.5 Bar. Turned on air conditioning to turn on fans. Seemed to increase pressure and idle slightly.

Got some oil and will change it out this week.

Maybe the fans is a solution to a problem that is not there, as you say. Still, I thought of doing it anyway even before this. Be really simple.

Macster

Fail to see how switching from 0w-40 to 5w-40 will make any difference in hot idle oil pressure since both oils have "40" as the high temperature/high sheer viscosity index which is measured at 212F.

0w-40 is fine. That is not the problem. (BTW, in my Dodge Hellcat in which I run a 0w-40 oil (Pennzoil) even at 230F the hot idle oil pressure only drops by around 2 or 3 psi from what it is at 212F. Roughly at 212F it is 40/41psi and at 230F it drops to 37/38psi. A bar is a bit over 14psi so a 3psi drop is just 1/4 a bar.

(When I switched from 0w-40 to 5w-50 my 996 Turbo hot idle oil pressure didn't change. The "50" is not really a thicker/heavier oil it just has a better high temperature/high sheer number.)

Low oil pressure at low idle speed -- idle speed below the norm -- is not a low oil pressure problem but a low idle speed problem. Do not know what the idle speed is for a 996 engine but you need to know. For my Boxster it was I believe 740 +/- 40 range IIRC. It is 740 +/- 40 for my 996 Turbo and this is the same for both the manual and automatic equipped cars.

You need to be sure the engine idles at the correct RPMs. Not sure why it is not idling at the right RPMs. The only time I had any problem with a variable idle was with my Boxster when what proved to be a VarioCam solenoid/actuator was acting up. I noted the idle speed would fall to around 500 and to me it felt like the engine was going to die. Had the low oil pressure warning light flashed at around 500 RPMs I would not have been surprised. Gear driven oil pumps are not very efficient at low speeds. There's a reason why the idle speed is 740 and not 700 or 660, 620, 580, etc.

Next, unless you have already done this you need to be sure of the hot idle oil pressure with a reliable/trustworthy gauge.

Noz1974

Also consider if you think the car is running hotter than normal , this will make the oil thinner than normal and will reduce oil pressure at idle, also as has been mentioned might be worth changing the oil pressure relief spring and piston in the oil pump when you do the oil change !