Oil Pressure - Cold Start Warning

Good Morning Gents - I had a odd experience on starting my 2004 996 yesterday and this morning. Oil Pressure is normally high (pegged on 5) at start, but after running for about 20 seconds at idle, the pressure guage drops to 0 and I get a warning light on the console. Just before I can reach for the key to shut the engine down, the needle bounces back up to 5, and the warning message clears. This only happens when the engine is cold. This will happen once or twice and then stops once the engine has warmed up enough that the pressure starts to come off the top peg (5). Engine runs as normal, no odd sounds, no drop in RPMs or other abnormality. My question revolves around whether this is a sensor abnormality, or a possible problem with the oil pump. I am not familiar with the oil pump on a 996. The pump appears to be mechanically driven, correct? If so, I'm leaning toward a sending/sensor unit problem, but obviously a warning light like this raises the hair on the back of your neck. Thanks in Advance - Rob

Have you tried cleaning the oil pressure sender contacts? After that you might want to replace the sender before messing/dealing with the gauge cluster and/or wiring. Yes the oil pump is driven by the IMS tube, which is driven by the crankshaft.

Very typical of an oil pressure sensor going bad. They bounce all over the place giving the owner a heart attack.... at least the first time it happens.

Funny. This happened to me 2 days ago. Driving along, got the warning and the gauge went to zero. Pulled over and called Porsche Roadside and they said it's most likely a glitch in the sender. I was half mile from the dealer so I just drove there. Tech confirmed...it's there today, most likely for a sending unit

Maybe its the oil pressure relief valve sticking open? There's an upgrade on the valve, costs about $20 and takes less time to change it out than it does to get the car in the air. Probably the sensor, but changing the pressure relief valve is cheap insurance.

A similar thing happened to me today: JDA (just driving along) and a warning came up with a "ding" and an oil can symbol in yellow. Stopped to check the oil level electronically and it registered all bars (was at all minus two bars 3 days ago, and didn't put any in). I cautiously drove home and noted that the oil pressure stayed in the 4-5 range even when idling, check at home showed all bars - 2 again. Not sure but it sounds like I need to replace the oil pressure sender. Anyone had this experience?

Photos would be helpful as to the location of the oil pressure sender and the oil pressure relief valve (anyone). Just in case the same things happen to other 996 owners. The main owner being ME lol.

To the previous poster, there about a zillion threads on oil pressure sender, how to get to it, how to replace it, etc. Just search "oil pressure sender" in the 996 forum.

Thanks for the quick replies guys. I was in Dallas and had to drive back to Austin, so it was nice having this info . The problem hasn't resurfaced yet, but I think I'll be replacing the valve and the sender. San Rensho may be on to something - either the valve sticking open or stucking shut with the sending unit retrurning a value out of spec, causing the reading to go to zero and then eventually reset. Again, gracias.

Sorry, I don't think a broken pressure relief spring would cause this behavior. I would start with the sender first, and as recommended previously, try to clean the contacts first and make sure there is a good electrical connection on the unit before replacing it.

Ive been stressing over my oil pressure guage for the past two days.....i checked my oil level electronicaly and it indicated 2 bars less then full so i added about half a quart of oil and after letting sit i checked with dip stick and it was a little over the max. So i thought to my self no big deal and it will burn it off, but when i started my car the pressure guage didnt come down from the 4-5 mark until warm (which is normal) however, after fully warm now its never less then 2 1/2 -3 mark. Last night i sucktion out about a quart of the oil but im still having the same issue with the pressure being high. Any ideas why its behaving the same way even after getting the extra oil out?

996pp - the slight overfill shouln't result in excessive pressure, which is more a function of oil temperature/weight, rpms, engine condition, etc.. 2.5 -3 bar isn't ordinarily excessive.

Thanks for your input Mark I. But why did it happen just after i toped off the oil ? It was at 1-1.5 mark at idle before adding oil and now even after getting some oil out its still between 2-3 at idle.

Pressure sender Come up from the bottom with an extension, 19mm crows foot, wobble extension or universal joint + extension.

996pp: Good question. But, I just drove home from my office - outside temp 67F. Engine at operating temp throughout. Idle oil pressure above 2 bar. 5W40 . My wild guess is that what you are noticing is coincidental to the slight variation in oil level. Possible explanation is the difference in oil temperature at your present readings and what you've seen in the past. In any event, you have nothing to fear - good pressure readings.

Great info and photos FPB111.. Looks pretty easy to change and I bought the 19mm crows foot a month or so ago especially for this job. (when it comes up for changing that is). Hellishly expensive crow foot at $28 dammit.

Thanks Mark I. Its almost due for an oil change. ill update any changes if there are any. fpb111 (Frank) i also thought it might need a new pressure sender but since it happened as soon as i added the oil im kind doubting it.

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You have to be sure you are observing the oil pressure with the oil hot. While the coolant gage might indicate the engine is hot the oil may still be cool. This will have the oil pressure reading higher than normal. On a related note if you have the A/C on the radiator fans run all the time and this can keep the engine cooler than it would be with the fans off. Turn off the A/C to turn off the radiator fans. Let the engine idle a minute or two. If the reading is higher than you think raise the rpms up to 1200 to 1500 and hold for 30 seconds. Then let the engine return to idle speed and observe the oil temperature. You want to view oil pressure at hot idle, not at balmy idle.

Tnx Macster....when its cold its in the high 4 but after warming up it drops to 2-2 1/2 mark. When before topping off the oil and seeing that it was too much and draining some out it was at a little over 1 while iidle after warm up.

BTW how do i look at oil temp?

Very common - Oil Pressure Sender failure. I had my Indie change it at the same time he was doing spark plugs. Cost me not much more than the cost of the sender itself (since he was in there anyway !) No problems since then...