Oil pressure is low on the gauge at idle (less than 1 bar) and oil pressire warning light comes on.
The car is slightly overfilled with Delvac 5w40, ambient temperature around 90 degrees with 4 to 5 bar pressure on acceleration. no other variables after driving back from SITM and no oil pressure warnings until driving the car last week.
Any ideas?

 

Does oil pressure jump instantly when the car starts from cold? Or does it sit at <1 for a second then build to 5?

 

2 quarts of Lucas + 7 quarts of 20-50W works for my 191K+ motor
I have the same problem without the Lucas.

 

Mine did the same thing, less than 1 bar, warning light, warm outside, and after I drove it quite awhile. I hooked up a guage and it was actually reading 1.5 which I thought was still low. Most people report 3 bar.
However, I changed to mobile 1 15W 50 and 1 quart of lucas and it reads about 1.5 bar which I guess is actually 2.5 bar. The light no longer comes on. I want to try Amsoil just havent done it yet. My voltage guage also reads low about 1 volt.

 

Andre is correct a 5w- 40 oil is just too thin in viscosity when you start to see those ambient temps 90F and above and add to that stop/ start urban driving conditions . We see this at our work a lot in the summer months (we work on more 928 series than anyone else in Sydney Australia ) . A 15w-50 or a 20w- 50 will solve it . However if it has been running on a 5W-40 for more than 20,000 miles we have found on many occasions that these engines have a much higher percentage of camshaft chain spocket and cam lobe wear (quadcam ) and these are the only ones we are seeing with thrust bearing wear . Dont get me wrong I am not complaining because this use of 5W-40 oil in these engines that were designed in the very early 1970's is and has given us a lot of work . When I worked for a Porsche Dealership from the late 1970's to 1994 we only used Valvoline Formula GP50 whiched was recommended by Porsche Cars Australia (importers ) which was a 25w-50 . This was used with fantastic results ( no engine wear problems at all ) we even went club racing with this oil .Its no longer made and we now use in all Porsches up to 1991 Valvoline Max life 20w-50 which has the very inportant ZDDP additive for these older engines (top end protection ) that nearly all modern synthetics do not have . Regards . BB.

 

Have the thermo springs been changed recently in the pressure releif valve, just above the oil filter /oil sender?? If not It would be a good place to start , the parts are inexpensive and it does require the alt and possibly the powersteering pump to be moved to gain access, also changing to a higher viscosity oil would help

 

Mrmerlin on the older air/oil cooled 911 models this was a common update / repair , I am refering to the 1970's versions . on the 928 series all models the oil pressure relief valves and springs have given us no trouble at all , so long as its not partly held open with metal fragments ( engine damage ). This oil issue is rather relavent at this point in time because the exponent of using the Delvac 5w-40 Diesel oil in 928 Porsche cars I have just read on the Landshark website has according to this web site has disposed of his 928 I wonder why ? . How the worm turns . Rgards . BB .

 

This is a common problem and identified by cfc928gt. Classic symptoms are low oil pressure on start up when engine is hot (eg after pulling in for fuel after longish run). A faulty oil thermostat is the culprit.
I am no longer a member as left the board when I sold my s4 and GTS but search on oil pressure alarm and my experiences and thread - with cfc928gt's explanation - should come up about halfway down the second page. The thread is entitled "oil pressure warning ?? false alarm" and contains a link to the required part ( the site won't let me post links )

A cheap and easy fix. Hope it helps.

Mark

 

PS low visocity oil won't help but should never trigger low pressure alarms unless other factors contributing (such as faulty thermostat / regulator/ restricted flow to cooler)

 

Bruce, (BB = Bruce IIRC),
Can you elaborate more please as I am also experiancing lower oil pressure on the guage - already subject of another thread. Why after changing to Delvac is this happening?
Do I change back to 15W 50 which I used for the last few years with no problems?
Is it because it is a thinner oil or????
Thanks,
Roger

 

Are you referring to the oil thermostat going to the oil cooler? If so, many 928's on the road do not have either one (thermostat or cooler), and still experience this issue.

When I switched from 15w-50 Mobile 1 to 5w-40 Delvac not only did my oil pressure drop below one bar on hot days at idle along with brief moments of the warning light, but my lifters started clicking whenever the pressure was this low.

So as I threw out there as a “theory” in the other thread, maybe no oil cooler combined with 100,000+ mile engine needs 50 weight vs. the 40? Who knows, now I’m running 50 weight again with no issues. If the pressure / clicking issue with 40 weight is a sign my engine is waving good buy, I’ll drop in one of my spares when this one goes defcon 4.

 

This is a new problem that started after more than two years using Delvac. The ambient temperature was far below those experienced in Texas and the oil hasn't changed so it's the car, not the oil or the temperature.

 

Here is an idea for you. go out and get 9 quarts of redline or Amzoil and watch the oil pressure go up to 3 bar at idle and 5 bar above 2k. in 90 degree temps i found the old mobil1 would basically turn to water. anway, you know my feelings and real world racing experience using redline or amzoil.

mk

 

Mark,
With all due respect, I'd rather find the cause of the incorrect reading and use oil that's been objectively tested and been shown to be superior. I've always preferred science to opinion.
Dave,
I haven't observed what happens to the pressure reading on start-up. What should I be looking for and what is the significance?

 

Mine is just age and wear. On days when it is 90-106 outside, even water wetter does not remove the engine heat enough to allow the oil to not breakdown. The same setup in the winter and it never goes below 3 bars, but in Fresno @ 106, 1-1.5 bars in the norm for idle.

It is a trade off between thick startups or water during running.

Lucus is your friend as long as they are not doing your eletrical!