Oil Pressure

There had been a thread several months ago about low oil pressure at idle on an '87S4 and that this is a potential problem that can easily be fixed although no one seemed to know how, there was just a part # that wasn't referenced in the shop manual (at least not in mine that covers up to MY '88).  I finally found out where the pins go and how to replace them. 
Since many of us are pulling off our cam covers to refinish and reseal this is a good time to perform this fix.  Apparently earlier 928s had longer cams that went all the way to the back cam cover bridge (firewall end). You'll notice looking at the cams on your '87 that on the back cylinders (4 and 8)the cam ends at the cam lobe for those cylinders rather than being supported all the way to the back bearing (hope this makes sense, take a look at yours).  The cam cover bridge in the back has some plastic oil seals that you should replace while you're in there.  They plug the oil journal to what used to lube the end of the cam.  Since the cam doesn't come all the way to the end but there is still an oil journal, if the pin isn't in place oil just squirts out the holes (approx 1/16 to 1/8" diameter).  The fix is to take the back bridge off and replace the old seal with either part #928.105.261.02 (see TSB #GRP 1 8711 which specified this part #), which is a round rubber seal the same diameter as the cam with a metal pin sticking out that goes into the oil journal, or a pin (no rubber seal), part # 928.105.262.00 (I believe this was used in later year cars).  I'm going to use the one with the rubber seal, it plugs the hole where the cam would ride as well as the oil journal.  I hope that it will keep oil from getting to the back seals where it may leak.  The parts are dirt cheap and the repair pretty simple.

(1) On really hot days (90's) my 87 S4 A/T sometimes shows an oil pressure warning light while I am idling at stoplights and the gauge drops to around 1 bar - but it goes off when the car is moving again. On cooler days the gauge is at or slightly under 2 bars at stoplights and there is no warning light. Is this normal or a sign that something needs to be addressed? I am using Castrol Syntec 5W-50 and my coolant temp gauge is usually at the low middle range. (2) My speedometer needle drops more slowly than the actual speed of the car under deceleration, as if it's damped. Is this normal? (3) Is there any reasonable way to re-calibrate the speedometer? I bought my car with 17" GTS/C2 wheels and low-profile tires and the speedometer reads too fast, i.e. the wheel rpm's are higher than the original stock wheel/tire

Thanks in advance. Bill Schmaal


That is low for the oil pressure . The 1987-88 used a plastic plug / pin insert to block oil a camshaft journal (used with the longer 85-86 cams) over time these degrade and blowout which can allow too much oil to escape too easily so that at idle speeds the pressure is low . Porsche replaced these part # 928 105 261 02 with a simple tapered steel pin 928 105 262 00 which is driven into the oil hole .... Inspection requires removing a cam housing cover .

Jim Bailey
928 International


>At 11:59 AM 6/1/00 -0400, Matt Burleson wrote:
>Quick question with  regards to Oil Pressure.
>Of the two cars I have looked at, one manual and one automatic I found this

>With the manual the oil pressure varied with engine speed.
>With the automatic the oil pressure was always high.
>Is this the norm, or could it be a pump or gauge problem with the 5 speed?

Norm is:
zero pressure with engine not running (don't snicker - some of our listers had max oil pressure without cranking the engine!)

2 -3 bar at warm idle

5 bar at normal driving RPM

Anything else could be sender problems, wiring problems,  gauge problems, wrong oil, or engine problems, in about that order of probability.

Wally Plumley
928 Specialists


First -- Many thanks for all of the info posted here -- you've helped me fix many items and the advice on purchases has been tremendous !!

Now, here's my latest challenge -- I have a problem with an Oil Pressure Warning when the Engine is warm and at Idle (ie: Stop Light).

    Condition       Throttle    Pressure      Issue
    Engine Cold     Idle/WOT      5 Bar       No Problem
    Engine Warm     >1000RPM     >3 Bar       No Problem
    Engine Warm     700 RPM      2.5 Bar      Idiot Lights On

The Idiot Light in the Oil Pressure Gauge goes on and the Central Warning System Flashes the Error Message.  Once the RPM exceeds 1000, the messages go away. 

From all of the posts that I have read in 928OC Archive, the Warm Idle Pressure is acceptable (ie: >1.5 Bar).  I believe the above gauge readings to be accurate.  The P.O. had the mechanic replace the Oil Sending Switch, but there was no improvement.

I'm looking for some thoughts on what to look for.
I'm going to check the following:
   1) Central Warning System Module Leads for Corrosion
   2) Run Component Function Test for Oil Pressure (Shop Manual p90-36).

As you would expect, I don't take Oil Pressure Warnings Lightly !!
Thanks in advance for all of the advice/recommendations !!


The 928 oil pump high pressure bleed - off is set at 9 bar so cold the engine and sending unit could see as much as 9 bar of pressure . Once warm , pressure depends on several things such as the type of oil , weight of the oil , idle speed of the engine , and how hot it really is. The brown , very brown 1980 after 30 minutes " racing " in 90 degree weather with the water temp on the last white line (hot) at idle at 900 rpm only has about 1.5 bar pressure but at 5,000 rpm is back at 5 bar . At normal temperature , normal driving it holds the 3-5 bar range which most people should see .

Jim Bailey


Good Afternoon.

The engine oil light in the instrument panel on my blue '87 comes on and blinks a couple of times in conjunction with the "!" for a couple of seconds after starting the car. The oil level is correct. Any thoughts on what is going on? I have never noticed this problem before on either of my cars.

Thanks in advance for any advice.

Larry Gunter


This is the way the engine oil level warning works:
The light will flash if the oil level is low when the engine is not running.
When the alternator output comes up to 12 volt, the oil level warning is switched off.

This is because the oil level is expected to drop when the engine is running.

What is probably happening to you is that the engine revs are not enough for the alternator to kick-in. Blip the throttle to get the alternator warning light to go off, then the oil level warning light will go off too.



>John McDermott wrote:
>Got the car all finished off after my alternator fix. Took it for a  good run down the highway. All is well. Pulled off and stopped at the light and the red idiot light starts flashing. Oil pressure is  pegged at 5+ even at hot idle. Rev the engine a little and the light goes off. Let it idle the light flashes again. Hmmm. Perhaps I  wired the oil pressure sending the wrong way round. Get to my house, pull into the garage, disconnect the oil pressure sender and swap  wires. Tighten one connection, tighten second and woops the threaded post comes loose and a little oil drops out. So, two questions:
1. is the oil pressure sending unit polarity sensitive?

2. can it be changed without draining the oil?
>John McDermott
>1982 928 Pacific Blue Metallic

The oil pressure sending unit includes two separate circuits: the idiot light and the pressure gauge. Both use a chassis ground.

It's a common problem to wire it backwards. That makes the gauge peg when the engine is running. It's also a common problem to twist off the internal wires.

This can be changed without draining the oil pan. Some may dribble out but it's not a torrent.

The blue/white wire goes to the terminal marked "G" (for the gauge) and the blue/black wire goes to the "WG" terminal. (for the idiot gauge?)



Oil pressure on the 928 GT at tick over is 2 bar and 5 bar on the move above 2000rpm. At the Ring, with water temperature at 100, oil pressure is 1.5 bar at tick over and 5 bar at over 4000 rpm. Oil used is Mobil 1 Delvac 5W40
The 928 S2's oil pressure is 2.5 bar at tick over and 5 bar on the move above 1800rpm. At the Ring, with water temperature at 100, oil pressure is 2 bar at tick over and 5 bar at over 3000rpm. Oil used is Castrol GTX 10W40


The info bouncing around the web forum was that 1.5 to 2 bar at idle when hot is normal.


Didn't keep a log book so the memory will have to suffice. When hot at 3K RPM:

Castrol 20w50 2.5 bar
Mobil1 15w50 3.5 bar
Amsoil TRO 20w50 5 bar


I would say pressure at 2 bar at idle is normal (could be wrong) but if you feel it isn't normal and it is a camshaft problem then I would say the first thing you should look at is the non return valve to each head. If the non return valve O ring has failed because it is 18 years old then oil just leaks from the pressurized oil pump feed into the cam housing and then back into the sump. There is no external indication that this happens and generally not enough loss of oil pressure to light up any warnings but it happens.

Jon in NZ


My GTS shows 5 when driving, and when it is really hot, maybe 4.5 at 2500 RPM.
3 Bar at idle or traffic jam is really ok. My car has been at 1.5 at idle some time when it was really hot. All in the green area, no alarms

Oil pressure went back to 2-3 bar at my S4. Most important: it was at 5 bar when revving above 2500.

after 5 rounds at the Spa Circuit, 28C outside temp, Coolant at 95C, oil pressure was 1,5bar at idle.

Above 2500 Rpm pressure was way above 3 bar despite of those conditions.
Oil was Castrol 15W40 Protec.

HP 89/S4
At a GTS, seen at a oil change, you can get a warning: low oil level. It is sensed by the level sensor in the top-front of the pan. When the engine is hot, idle pressure should not get below 1.5bar, above 2000 rpm on 3,5

Be aware that the hot climate radiator is in front of the coolant radiator, thus increasing the coolant temp a bit.


This for a 2 pin sensor:
5 bar 185 ohms
4 bar 160 ohms
3 bar 130 ohms
2 bar 95 ohms
1.5 bar 75 ohms
1 bar 55 ohms
Low pressure switch- changeover point about 6 psi
Accuracy is not perfect, allow 10% off.