Will Oil Make A Difference "Yes it Does"
10-24-2009, 06:56 AM
#46
Rennlist Member
Brett,
All the 928's I have seen here show about 2 barg when hot but can go to 5 barg when cold starting. Although the UK can freeze your nuts off ieven n summer, it is not that cold to explain why you see the reading you do. In that regard I like the explanation about the condition of your elecrical connections which may be compromised by dampness and age in good old blighty.
The hydraulics are quite simple to explain. At low speeds the pumps do not push much oil [they are positive displacement so low speed=low flow] hence little back pressure unless the oil is cold and hence more viscous creating more drag hence more pressure to overcome the resistance to flow. At 5 barg the relief valve opens irrespective of what flow is being maintained.
Any notion that 2 barg indicated at tickover "suggests a problem" is not correct. If pressure goes above 5 barg then something is definitely wrong either mechanically or electronically. A 20w50 oil will generate higher initial presure compared to say a 0w40 and at temperature will hold a higher pressure at tickover when hot. However, a 20w50 oil will not flow as freely as an oil with less viscosity and hence the thicker oil will cause the engine to run hotter as it does not cool the motor as well. Hence why I feel I ned more oil cooling having gone back to 20w50 oils.
Regards
Fred
Regards
Fred
All the 928's I have seen here show about 2 barg when hot but can go to 5 barg when cold starting. Although the UK can freeze your nuts off ieven n summer, it is not that cold to explain why you see the reading you do. In that regard I like the explanation about the condition of your elecrical connections which may be compromised by dampness and age in good old blighty.
The hydraulics are quite simple to explain. At low speeds the pumps do not push much oil [they are positive displacement so low speed=low flow] hence little back pressure unless the oil is cold and hence more viscous creating more drag hence more pressure to overcome the resistance to flow. At 5 barg the relief valve opens irrespective of what flow is being maintained.
Any notion that 2 barg indicated at tickover "suggests a problem" is not correct. If pressure goes above 5 barg then something is definitely wrong either mechanically or electronically. A 20w50 oil will generate higher initial presure compared to say a 0w40 and at temperature will hold a higher pressure at tickover when hot. However, a 20w50 oil will not flow as freely as an oil with less viscosity and hence the thicker oil will cause the engine to run hotter as it does not cool the motor as well. Hence why I feel I ned more oil cooling having gone back to 20w50 oils.
Regards
Fred
Regards
Fred
10-24-2009, 08:49 AM
#47
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Well im hitting 5's at cold and hot and i dont know what oil i have or if the oil sender is working correctly(just bought her a week ago), but im only at just over the 1/4 mark on temp never higher (i do give her a hummering) so i bought some Mobile 1, 5w-50 full synth (superSynth) also oil filter(oem) I plan to have the engine Washed/flushed before using new oil...god knows what oil is in there now and what condition the filter is like!
10-24-2009, 01:16 PM
#48
Race Car
It is mechanically not possible for a 928 to have a 5 bar of oil pressure at below 1,000RPM when the oil is fully warmed up unless it has SERIOUS engine problems (which would most probably prevent the car from running in the first place) or a problem with the pressure sensor, gauge and/or their wiring. No automobile engine oil or climate on this planet could cause this. Unless they are now making 150 weight engine oil?
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
10-24-2009, 05:36 PM
#49
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I was using valvo vr-1 20w50 and would idle at 3 bar or so. I switched to AMsoil 20w50 and it ticked up between the 3 and 4 bar reading. I would figure it maybe overfull if reading 5 bar when hot, or the pressure sender is bad.
10-25-2009, 04:08 AM
#50
Reanimator
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Rennlist Member
Is this the first car so many of you have had with an oil pressure gauge? I'm kind of amazed at the panic of less oil pressure at idle; that's pretty much a universal finding. Besides, there are many other threads addressing this.
10-25-2009, 05:14 AM
#51
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My car has had zero oil pressure for a few years now.....
Note to self - install engine....
Note to self - install engine....
10-25-2009, 08:46 AM
#52
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OK now i have a better example of my oil pressure:
Cold hits 5
after 5mins driving stays around 4-5
at a warm to hot (leaving the car to idle for 10mins after driving for 20mins) hits 3.5
now thats better , maybe i fixed the issue after i gave the engine bay a good clean and detail to the wiring... car felt smoother
Cold hits 5
after 5mins driving stays around 4-5
at a warm to hot (leaving the car to idle for 10mins after driving for 20mins) hits 3.5
now thats better , maybe i fixed the issue after i gave the engine bay a good clean and detail to the wiring... car felt smoother
