My oil pressure used to read 5 bar constantly...now it doesnt
11-23-2007, 11:36 AM
#1
Advanced
Thread Starter
Join Date: Aug 2007
Location: San Francisco, CA. '84 US 928S; Auto; RauchQuartzMetallic. 60K miles
Posts: 59
Likes: 0
Received 0 Likes
on
0 Posts
My oil pressure used to read 5 bar constantly...now it doesnt
Hey sharksters,
Ive had this shark for 5 months now...and I seem to remember that it was always at 5 bar (I think).
Now recently, I noticed it starts at 5 bar, but about 15 minutes later it settles into about 3 bar.
Now I cant remember what is normal.
Can someone illuminate me?
Ive had this shark for 5 months now...and I seem to remember that it was always at 5 bar (I think).
Now recently, I noticed it starts at 5 bar, but about 15 minutes later it settles into about 3 bar.
Now I cant remember what is normal.
Can someone illuminate me?
11-23-2007, 12:34 PM
#3
Craic Head
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Check this out:
https://rennlist.com/forums/showthread.php?t=375886&referrerid=45339
(agrees with Andrew pretty much
)
https://rennlist.com/forums/showthread.php?t=375886&referrerid=45339
(agrees with Andrew pretty much
)
11-23-2007, 03:12 PM
#4
Burning Brakes
Join Date: Dec 2002
Location: Airlie Beach, Australia
Posts: 870
Likes: 0
Received 0 Likes
on
0 Posts
Hi,
this is data from the previous Thread on idle OP
I did not post it as the Thread had run its course - it may be of interest now;
AN UPDATE OF THE PREVIOUS DATA - Hot idle oil pressure
There is probably enough data now to overcome variances in actual oil temperatures and the like, so these results are quite meaningful
The data confirms that 1.5 to 2.5bar is the "normal" hot idle OP range for most 928s with around 70% of all engines being in this range. Approx. 29% of these were right on 2bar, 33% were between 2-2.5bar and 9% showed between 1.5-2bar.
Only 1 vehicle showed less than 1.5bar! This engine also showed less than the required minimum of 5bar at 4000rpm with both SAE40 & SAE50 lubricants. This suggests that there may be an issue with the engine!
80% of the respondents use one of seven Brands of synthetic oil. Mobil was by far the most popular Brand with 50% of users confirming its WW Market Share position, performance, reputation and ready availability. 15% were using a Castrol mineral or synthetic lubricant
IMHO this exercise confirms again the relevance of Porsche's Approved viscosities for everyday (non racing) use in a 928 engine
A - Hot idle OP
Average of all viscosities = <2.4bar
Median of all viscosities = 2.5bar
Average of all SAE40vis. = 2bar
Average of all SAE50vis. = 2.5bar
Average of 0w-40vis. = 2.1bar (a Porsche Approved Vis.)
Average of 5w-40vis. = 2.1bar (a Porsche Approved Vis.)
Average of M115w-50 = 2.5bar (most popular here at 30% of respondents)
Average limited to <5w & <SAE50 = 2.1bar (within Porsche Approved vis. limits)
Average limited to >5w to >SAE70 = 2.5bar (outside Porsche Approval vis. limits)
B - Averages according to the lubricant's "cold" viscosity rating (open ended upper viscosity);
0w = 2.1bar
5w = 2.1bar
10w = 2.6bar
15w = 2.4bar
20w = 2.6bar
Note that the Approved viscosity lubricants 0w-40, 5w-40 and 5w-50 averaged 2.1bar
C - It is interesting to note that the heaviest lubricant (a "synthetic" 10w-70) showed a near average hot idle OP of 2.5 in one case. Both engines using it were only slightly above average OP at 2000rpm! It is however 60% thicker than M1 15-50 at 5C and 53% thicker at 10C - common cold start temperatures in many regions. It is also still 60% thicker than M1 15w-50 at 90C which is a typical 928 operating oil temperature
It was 2.25 times thicker at 5C than the 5w-40 Approved viscosity lubricant
By contrast the lightest lubricants, SAE40 (0w-40), all showed >2bar at a hot idle!
D - Averages by MY,type or model (all viscosities);
All <MY85 = 2.5bar (anomalous, believed to be about 2.2bar)
All Quad-cam to GT = 2.6bar
GT = 2bar
GTS = 2bar
SUMMARY
For later engine families Porsche has published a WSM hot idle OP of "approx. 1.5bar" and "approx. 5bar at 5000rpm" and after this exercise it's logical that this same relationship can be applied to a 928. The oil's temperature must be at or near 90C and the oil must be a Porsche Approved viscosity as 0w-40, 5w-40 or M1 0w-50
"More" OP is NOT necessarily "better" at a hot idle. It is worth noting that OP warning lights are generally triggered at or below 0.75bar (11psi). This has been so for the last several decades.
Depending on the engine's design, once under about 0.4bar (6psi) at idle, the journal bearing clearances caused by the "wedge" effect of the lubricant flow may be lost resulting in excessive wear as the lubricant loses its ability to maintain a suitable film thickness. Above 0.5bar the lubricant's "wedging" effect and low engine load at idle will combine to maintain adequate lubrication
Lubricant Flow (volume per engine rev) remains the same of course but parasitic losses can be greater at idle speed. Too much pressure at idle can increase these and decrease the lubricant's ability to carry heat away to the sump.
As shown in some DEVEK Dyno tests several years ago it takes some considerable time for the OP relief valve to close with revs over around 2000rpm using cold oil. The lubricant used in Marcs test (M1 15w-50) has quite good low temp. flow characteristics too!.
Thicker cold mineral oil significantly extends this period. In this position considerable oil volume short circuits the lubrication system and/or is not filtered due to the actions of the full flow filter's by-pass valve and the type of filtration media used
Regards
this is data from the previous Thread on idle OP
I did not post it as the Thread had run its course - it may be of interest now;
AN UPDATE OF THE PREVIOUS DATA - Hot idle oil pressure
There is probably enough data now to overcome variances in actual oil temperatures and the like, so these results are quite meaningful
The data confirms that 1.5 to 2.5bar is the "normal" hot idle OP range for most 928s with around 70% of all engines being in this range. Approx. 29% of these were right on 2bar, 33% were between 2-2.5bar and 9% showed between 1.5-2bar.
Only 1 vehicle showed less than 1.5bar! This engine also showed less than the required minimum of 5bar at 4000rpm with both SAE40 & SAE50 lubricants. This suggests that there may be an issue with the engine!
80% of the respondents use one of seven Brands of synthetic oil. Mobil was by far the most popular Brand with 50% of users confirming its WW Market Share position, performance, reputation and ready availability. 15% were using a Castrol mineral or synthetic lubricant
IMHO this exercise confirms again the relevance of Porsche's Approved viscosities for everyday (non racing) use in a 928 engine
A - Hot idle OP
Average of all viscosities = <2.4bar
Median of all viscosities = 2.5bar
Average of all SAE40vis. = 2bar
Average of all SAE50vis. = 2.5bar
Average of 0w-40vis. = 2.1bar (a Porsche Approved Vis.)
Average of 5w-40vis. = 2.1bar (a Porsche Approved Vis.)
Average of M115w-50 = 2.5bar (most popular here at 30% of respondents)
Average limited to <5w & <SAE50 = 2.1bar (within Porsche Approved vis. limits)
Average limited to >5w to >SAE70 = 2.5bar (outside Porsche Approval vis. limits)
B - Averages according to the lubricant's "cold" viscosity rating (open ended upper viscosity);
0w = 2.1bar
5w = 2.1bar
10w = 2.6bar
15w = 2.4bar
20w = 2.6bar
Note that the Approved viscosity lubricants 0w-40, 5w-40 and 5w-50 averaged 2.1bar
C - It is interesting to note that the heaviest lubricant (a "synthetic" 10w-70) showed a near average hot idle OP of 2.5 in one case. Both engines using it were only slightly above average OP at 2000rpm! It is however 60% thicker than M1 15-50 at 5C and 53% thicker at 10C - common cold start temperatures in many regions. It is also still 60% thicker than M1 15w-50 at 90C which is a typical 928 operating oil temperature
It was 2.25 times thicker at 5C than the 5w-40 Approved viscosity lubricant
By contrast the lightest lubricants, SAE40 (0w-40), all showed >2bar at a hot idle!
D - Averages by MY,type or model (all viscosities);
All <MY85 = 2.5bar (anomalous, believed to be about 2.2bar)
All Quad-cam to GT = 2.6bar
GT = 2bar
GTS = 2bar
SUMMARY
For later engine families Porsche has published a WSM hot idle OP of "approx. 1.5bar" and "approx. 5bar at 5000rpm" and after this exercise it's logical that this same relationship can be applied to a 928. The oil's temperature must be at or near 90C and the oil must be a Porsche Approved viscosity as 0w-40, 5w-40 or M1 0w-50
"More" OP is NOT necessarily "better" at a hot idle. It is worth noting that OP warning lights are generally triggered at or below 0.75bar (11psi). This has been so for the last several decades.
Depending on the engine's design, once under about 0.4bar (6psi) at idle, the journal bearing clearances caused by the "wedge" effect of the lubricant flow may be lost resulting in excessive wear as the lubricant loses its ability to maintain a suitable film thickness. Above 0.5bar the lubricant's "wedging" effect and low engine load at idle will combine to maintain adequate lubrication
Lubricant Flow (volume per engine rev) remains the same of course but parasitic losses can be greater at idle speed. Too much pressure at idle can increase these and decrease the lubricant's ability to carry heat away to the sump.
As shown in some DEVEK Dyno tests several years ago it takes some considerable time for the OP relief valve to close with revs over around 2000rpm using cold oil. The lubricant used in Marcs test (M1 15w-50) has quite good low temp. flow characteristics too!.
Thicker cold mineral oil significantly extends this period. In this position considerable oil volume short circuits the lubrication system and/or is not filtered due to the actions of the full flow filter's by-pass valve and the type of filtration media used
Regards
11-23-2007, 04:08 PM
#5
Race Director
Your pressure sounds normal
When the pressure sender fails (common) it will peg the sender at 5 bar all the time.....no matter if the engine is warm or cold.......but its only around $50 and easy to change
When the pressure sender fails (common) it will peg the sender at 5 bar all the time.....no matter if the engine is warm or cold.......but its only around $50 and easy to change
11-23-2007, 07:43 PM
#6
Drifting
Join Date: Nov 2001
Location: zürich, switzerland
Posts: 2,233
Likes: 0
Received 0 Likes
on
0 Posts
The oil pressure relief valve pops open about 8 bar.
So your shark should show 8 bar at cruising speeds.
But the gauge only goes to 5 so expect 5 at cruising speeds & higher
Marton
So your shark should show 8 bar at cruising speeds.
But the gauge only goes to 5 so expect 5 at cruising speeds & higher
Marton
11-23-2007, 09:39 PM
#7
Three Wheelin'
Join Date: Jun 2005
Location: Bournemouth, Dorset, UK.
Posts: 1,741
Likes: 0
Received 1 Like
on
1 Post
Hi
Your loss of pressure MAY be connected to your possible Head Gasket failure...I wont go into the technical side now but get that "block test" done as I said in your other thread...
IF your loss of pressure IS caused by the coolant loss YOUR ENGINE WILL BLOW SOON !!!!!!
GET IT CHECKED NOW!!!!!!!!!!
All the best Brett
Your loss of pressure MAY be connected to your possible Head Gasket failure...I wont go into the technical side now but get that "block test" done as I said in your other thread...
IF your loss of pressure IS caused by the coolant loss YOUR ENGINE WILL BLOW SOON !!!!!!
GET IT CHECKED NOW!!!!!!!!!!
All the best Brett
Trending Topics
11-24-2007, 02:56 AM
#8
Doug
Thanks for that excellent summary and all the other oil expertise you've shared.
Jaimsey
Did you change the oil recently. Different (lower viscosity numbers) oil will have that effect .
Colin. 9GT
Thanks for that excellent summary and all the other oil expertise you've shared.
Jaimsey
Did you change the oil recently. Different (lower viscosity numbers) oil will have that effect .
Colin. 9GT
11-24-2007, 12:37 PM
#9
Rennlist Member
that's how mine reads...where is the pressure sender and what do you need to do to change it? I just had the pod off, and the needle is fine, so it must be the sender?
