My S2 which has 96k miles has 3.5 bar at highway speeds it was 4.5 bar when I bought the car at 82k 2years ago... It has 5 Bar at start up and 2.5 -3 bar at idle. should I be concerned ? Is the oil pump gradually failing ? Or just normal for age of motor. How low is to low ? drop has been gradual. I did change oil pressure sender 6 months ago when pressure was erratic on guage, and this did fix that issue , dont think they are connected . BTW I run Redline 10 -40. was thinking if I switch to 20 -50 presure might increase. Again how low is to low at highway speeds ? Car is meticously maintained and runs fantastic otherwise.
Thanks for any input dont wanna fry the motor.
1990 944 S2 cab triple black

 

For comparison...

My S2 with 207,000 miles.....startup = 5bar, warmed up/hot at idle = 2 bar....while driving = 4.5 to 5 bar.

I had a fright a few years ago at the track...needle bouncing up and down....sitting at below 1.5 bar at hot idle after laps. Turned out to be a bad sensor.

If I were you I'd change the sensor....put a fresh one in. That way you know at least you're getting proper readings.

Check here via search but I believe you will find most are not using 10w40

 

It could be that your bearings have worn, opening up and dropping pressure. Has it been hotter where you are lately? Is your car running hotter temp wise? Either will thin out the oil, but i would put some 20 50 in and see if it improves.

 

944's need 20w-50

 

10w40 might be okay for winter use, but you should be running 20w50 in the summer.

The operating oil pressure notes vary among the different 944/968 models' factory work shop manuals. For the most part, they state; about 4bar at 5K rpm when at operating temperature. I've also heard the general rule of a minimum 1bar per 1k rpm, from an engine builder.

 

i was surprised when i installed a manual oil pressure gauge in my spec car, the fact. gauge always read low but the manual gauge showed 70psi at start up- 100psi if you rev it.

 

How exactly do worn journal bearings lower the oil pressure?
Thanks!

 

More clearance, more oil seeping by= less pressure.

 

Operating temperature will alter the oil pressure, it is actually the temperature of the oil tho that changes the pressure. I have an oil temp gauge in my truck, IIRC when oil temp is 210F the pressure is 64-67 lbs, when 230F it is only 53-55 lbs at the same RPM. BTW I run Mobil One 15W-50 synthetic in my '83 NA.

 

Thanks for the input , and Jamesr, thanks im quite certain it is temp related ... oil temps will rise and fall while the Water temp guage stays put im sure ... However im still thinking 50w is a good idea in the summer for exactly this reason and i will definitly be doing that...
Just seems funny though the last 2 summers I always had 4.5 bar with same oil. driving the same (hard )

 

2.5 bar is 50 psi assuming your driving in top gear and the revs are 2k-3krpm that sounds perfect.

The temp of the oil will have a huge impact on the pressure.



And why do you guys think Porsche 944's need 20w-50?

 

Excuse me but 2.5 bar is more like 36.75 psi (14.7 times 2.5 )
So im running 51.45 psi at highway speeds ( 14.7 times 3.5 )
Correct me if im wrong but a Bar is 14.7 psi ( atmospheric pressure at sea level )

 

Sorry I mistyped 3.5. Bar as theOP said . 50 psi still.

My fingers are to big for this phone.......

 

The second number in 20W-50 refers to the viscosity at higher temp, and the first is the viscosity at colder temp (IIRC ,it's at 32F). So at higher temps you would want a higher number to maintain the correct viscosity. If you were driving the family car/van, the higher viscosity at extreme temps wouldn't matter because you aren't pushing the vehicle hard. Hence you want 10W-50 to 20W-50, ideally. 15W-40 (diesel oil) would work if that's all that's available.

 

OK now the next obvious question ... who make a good high in ZDDP oil ? Synthetic of course.