928BC

1979 5sp 180000 KM
Summer:
Castrol GTX 20/50
5 Bar @ cold idle
2 Bar when HOT @ idle
4 bar When HOT @ 3000 RPM and up

Winter:
Castrol GTX 10/40
5 Bar @ cold idle
2 Bar when HOT @ idle
5 Bar when HOT @ 3000 RPM and up

Of Course all readings taken using the highly accurate and calibrated pod gage.

Mike Frye

Robbie,

Your point is a good one, and this thread isn't an attempt to figure out exactly what pressure the cars are running at, I just wanted to see what is considered 'normal' and if there was a difference between one year and another.

It seems that the indicator system didn't change at all throughout the years, which is interesting. I guess the digital dash made the display different, but the sending unit design stayed the same as nearly as I can tell.

I looked up the conversion from bars to psi and (at sea level) here's what I got:

5 BAR = 72.519 PSI at 0 FT Above Sea Level
4.5 BAR = 65.267 PSI at 0 FT Above Sea Level
4 BAR = 58.015 PSI at 0 FT Above Sea Level
3.5 BAR = 50.763 PSI at 0 FT Above Sea Level
3 BAR = 43.511 PSI at 0 FT Above Sea Level
2.5 BAR = 36.259 PSI at 0 FT Above Sea Level
2 BAR = 29.008 PSI at 0 FT Above Sea Level
1.5 BAR = 21.756 PSI at 0 FT Above Sea Level
1 BAR = 14.504 PSI at 0 FT Above Sea Level

OK,
Now that I've gotten all the responses I expect to get (about 30 is pretty good, but not what I would call a representative sample) I'll open the door for the oil pressure question:

The manual doesn't seem to list a minimum pressure, nor does it list a 'normal' operating range (that I can find) but it does list that over 4k (or 5k as Bill Ball mentioned in another thread) it does say it should be reading 5 bar.

If the minimum pressure at idle is not specified (as long as the warning light is working properly and not lit) but a minimum 'high rpm' pressure is specified, then I would think that the only numbers that the designers were concerned with were that the pressure is at 5 bar under heavy load. I take this to mean that the designers felt that a minimum of 5 bar of pressure (about 70psi at sea level, standard atmospheric conditions) was required at the sending unit for the engine oil system to get oil throughout the system efficiently enough for prolonged operation.

By using the trans-sociative property, does this mean that if the indicator system is working correctly, and your gauge reads less than 5 bar at 4k+ rpms, that your engine is in danger of oil starvation?

I think this is what Mark Kibort has been saying all along about some oils in some applications, and I'd like to know if my logic is flawed or if there are just too many assumptions along the way to make a valid argument either way.

ziim

80` Euro 928 (K-Jet is replaced with L-Jet)

Castrol RS 20(?)/60

Idle when cold: 5 bar
Idle when warm: ~3
Reading at 5krpm: 5
Mileage: about 100k

sharkmeister85

I read somewhere that an engine (any make/model in general) should have 10 psi of oil pressure per 1000 rpm to establish proper oil flow. I don't know if this is some sort of "engineering" formula and haven't been able to find anything to verify it. If this is indeed true, then 3 bar at 4k rpm would be sufficient.
Glenn

ziim

IMO it`s more-less ok, not what it`s should be, but ok.
If I`m wrong, others know what to do

svp928

85 5sp
MOBIL 1 15-50

Cold idle 5bar
hot idle 3
hot 5bar at 2k rpm
hot track day 2.5 idle
5 bar at 2k rpm

mark kibort

I want to see a jpeg of 2krpm and 5 bar pressure
it took near 4000rpm to get 5 bar with scots car running mobil 1
Thats good if its true.

mk

Doug Hillary

Hi,
this thread has been very meaningful and helpful.
IMHO it would have perhaps been more so if it had also asked;
a) how long the engine had been running before its "hot" idle OP was taken (a minimum of 30 minutes under load is needed - 90C oil temp. is needed ) and,
b) at what "hot" engine speed was 5bar OP (Porsche's minimum) first reached

Note 1: As Porsche has published a hot idle OP of "approx. 1.5bar" and "approx. 5bar at 5000rpm" for later engine families it's logical that this relationship can also be applied to a 928

A QUICK SUMMARY OF THE FOLLOWING DATA
(Data ex this Thread and my own OZ UOA etc database)

It appears that 1.5 to 2.5bar is the normal hot idle OP range for most 928s with 65% being in this range. Approx. 38% were right on 2bar, the greatest number at one datum point. 16% were between 2bar and 2.5bar, and 11% between 1.5bar and 2bar.
IMHO this exercise also confirms the relevance of the Porsche Approved viscosities

A - Hot idle OP
Average of all viscosities = 2.4bar (lowest 1bar (see below), highest 4bar(may be an error))
Median of all viscosities = 2.2bar
Average of all SAE50vis. = 2.6bar (lowest 1.5bar, highest 4bar (may be an error))
Average of all SAE40vis. = 2bar (lowest 1bar (see below), highest 2.5bar)
Average of 0w-40vis. = 2bar (Porsche Approved Vis.)
Average of 5w-40vis. = 2.1bar (Porsche Approved Vis.)
Average of M115w-50 = 2.6 (lowest 1.5, highest 4bar (may be an error))
Average limited to 5w and SAE50 = 2bar (Porsche Approved Vis. limits)
Average limited to 10w to SAE60 = 2.5bar (Vis. beyond Porsche Approval)

Approved viscosity lubricants 0w-40 and 5w-40 averaged 2bar

Averages by MY or model (all viscosities);
All to 85 = 2.5bar (corrupted due to anomalous numbers - avg. believed to be 2.1bar)
85-86 = 2.6bar
87-88S4 = 2.8bar
>89S4 = 2.6bar
GT = 2bar
GTS = 2bar

Note 2: The lightest oil 0w-40 (SAE40) showed at least 2bar (MY85 & MY89)
Note 3: The heaviest oil(s)10w-60 (SAE60) showed 3bar and 3.5bar (MY80 & MY89)

B - Engine Speed OP
The Porsche 928 OP min. of 5bar was reached by 22 engines prior to 3000rpm and
13 engines reached 5bar at or before 2200rpm. One engine reached 5bar at 1800rpm

Note 4: The MY93GTS engine with the lowest idle OP of 1bar with a 5w-40 lubricant DID NOT REACH the min. 5bar @ 5000rpm - it showed 4.5bar when using either a 5w-40 or a 15w-50 lubricant

Note 5: From data supplied some engines DID NOT ATTAIN 5bar at 3000rpm, or most importantly even at 5000rpm. Some more of these engines also recorded a low (below 1.5bar) hot idle OP! Some of these engines were on a 20w-50 lubricant

IMHO it gives cause to check/replace the OP relief valve spring and to check/replace the OC thermostat/spring too. It is probably a worthwhile job on all engines that are not showing 5bar by 3000rpm - especially those that are on a thicker 20w-50 lubricant!
In older cars the by-pass valve spring should be replaced as well - makes sense to me

Any engine that showed much more than 3bar at "hot" idle would worry me too!

DaveO pointed out how inaccurate the OP gauge is and IMHO this needs to be remembered

IMHO the only accurate way to measure OP is with a calibrated Master Gauge as has been mentioned earlier and by ensuring that the lubricant's temperature is stabilised at 90C

I hope this is helpful - it should be accurate

Regards

Mike Frye

Doug Hillary ladies and gentlemen.


Wow. I was just going to, like, use an Excel spreadsheet. I feel like I should close it or something now that he's weighed in with his analysis.

Thanks for the time and effort you put into this Doug.

And thanks to everyone who has contributed. Maybe more people can chime in (especially those with anomalous readings if there is any change due to service recommendations they got here).

Now I don't feel so bad about calling it the 'official' thread.

AO

Just to reiterate Doug and Dave's comments ont he inaccuracies of the analog gauge, just look at my thread I posted some time back about the differences between the analog and the digital readout from the digital dash.

https://rennlist.com/forums/928-forum/362566-928-digital-dash-and-oil-pressure.html

SwayBar

As usual, thank you Doug!

I was at PCA Chicago's Labor Day weekend event at Road America last week doing 3 days of DE's while running dino Valvoline VR1 Racing 20W-50 oil (..breaking in a new engine); with the engine ice-cold, the idle oil pressure is 100+ psi.

The following was observed at WOT on the front straight (..since I had time to look); with a clear lap with no one holding me up, I did consistent 2:38's (..a little disappointed in that, I'm just not in a groove yet with the car as I was with the Z06). The listed idle oil pressure is in the pits after coming in from a session, and the readings are from aftermarket electric-sender Autometer guages.

In the cool morning, low 70's with shade covering approx 85-90% of the track:

Water Temp: 180 F
Oil Temp: 190 F
Oil Pressure @ 5k: 75 psi
Oil Pressure Idle: 25 psi

In late morning, high 70's with shade covering approx 25-30% of the track:

Water Temp: 190-200
Oil Temp: 210
Oil Pressure @ 5k: 75 psi
Oil Pressure Idle: 25 psi

Afternoon, low-mid 80's, and virtually no shade on track:

Water Temp: 210
Oil Temp: 230 - 240
Oil Pressure @ 5k: 60 psi
Oil Pressure Idle: 21 psi

The first time I saw 60 psi on Friday, I freaked out and headed into the pits immediately at Turn 5. Once pitted, I shut the car down and checked the oil which looked like I just poured it into the engine: crystal clear. I let the car sit for at least an hour, and cranked it back up.

All values at idle:

Water Temp: < 140
Oil Temp: < 140
Oil Pressure Idle: 75 psi

...which are normal values, so I knew I was good to go. I had many sessions after that while running 60 psi oil pressure at 5k on the front straight with no problems.

The engine is broken-in now, so tonight I will be changing the oil to a synthetic, Mobil 1 15W-50.

sharkmeister85

Doug mentioned changing the OP relief valve spring on cars not seeing full OP at 5k rpms. My understanding of oil pumps is that they are commonly replaced when rebuilding engines in other makes because they wear out. Yet, I don't recall reading anything about our oil pumps wearing out or failing or being replaced. Am I mistaken here, or did Porsche put a "magic" pump in 928's that never wear out, and deliver consistent pressure across all oil grades and engine temperatures and engine mileage?. Could a worn oil pump be the cause of some 928's showing lower OP at higher engine temps using the lower viscosity oils?
Glenn

hacker-pschorr

Updated my post for yea

telidor99

Great Thread!

1981 Euro Auto 190K+

Mobel 1 15 W 50

Cold idle 5 Bar
warm 1.8-2.5
5000 RPM 5 Bar.

We all know the pod may not have great accuracy..but what numbers would be a sign of a problem? What would a sign of a bad oil pump?

Kevin in Atlanta

'93 GTS ('94 engine) with Mobil 1 15W50 94K miles

Cold idle 5 bar
Hot idle 2.5-3bar
Hot/Cold over 3k 5 bar