Oil pressure warning light at idle
07-01-2007, 11:30 PM
#31
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I too have the same problem and believe I have sourced a fault with my camshaft plugs which are made of plastic encompassing a small metal rod. As the plastic degrades it no longer does it's duty of sealing the holes, thus allowing your pressure to drop. These should be replaced anyway as your car gets older or when you go for the cam tower refinishing. It isn't a matter of if, but when will they fail as they are prone to heat degradation. I haven't had the time to remove my cam covers and complete the replacement yet as I have been involved w/ other areas of my car.
Take a look at the link from 928intl's website that covers this in detail.
http://members.rennlist.com/v1uhoh/nasty.htm
To reconfirm what others are saying, however, I would start first with inspecting/cleaning the spring associated with the oil pressure sending unit next to the oil filter. Although I can't recall where, someone posted this service w/ pics either here on Rennlist or the web.
Take a look at the link from 928intl's website that covers this in detail.
http://members.rennlist.com/v1uhoh/nasty.htm
To reconfirm what others are saying, however, I would start first with inspecting/cleaning the spring associated with the oil pressure sending unit next to the oil filter. Although I can't recall where, someone posted this service w/ pics either here on Rennlist or the web.
07-02-2007, 02:48 AM
#32
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Knowing the oil circuit, I think there are 2 areas to look for when a SUDDEN drop of idle oil pressure occurs:
1) Oil has just been changed, and is too light for the job. If oil has just been changed, regardless of what the oil manufacturer say, I'll change it again with oil from a different source.
2) Oil is getting hotter than usual, with or without coolant getting hotter than usual. Wrong or old oil filter (or clogged because funny friction reducing additives) or coolant not able to cool the engine down enough because of weak pump or blocked passages (because of funny sealing additives) or whatever other reason.
To my knowledge, too heavy oil makes a bit more temp in the oil, so a fraction worse mileage, and make more dangerous damage if the pressure relieve valve fails (never seen in my life). Also make startups more difficult. Too light will cause the oil film to brake in high revs high temp, destroying the engine, even if you still see a 5 in the gauge.
Any problem bleeding oil back to the pan is unimportant as long as pressure builds up quick to 5 with revs, as it's exactly the same thing the max pressure valve does all the time. The real important thing is having a proper oil temp (below 130º hot, easy with an unexpensive thermocouple or any other old temp sensor) and a proper oil weight for that temp (50).
1) Oil has just been changed, and is too light for the job. If oil has just been changed, regardless of what the oil manufacturer say, I'll change it again with oil from a different source.
2) Oil is getting hotter than usual, with or without coolant getting hotter than usual. Wrong or old oil filter (or clogged because funny friction reducing additives) or coolant not able to cool the engine down enough because of weak pump or blocked passages (because of funny sealing additives) or whatever other reason.
To my knowledge, too heavy oil makes a bit more temp in the oil, so a fraction worse mileage, and make more dangerous damage if the pressure relieve valve fails (never seen in my life). Also make startups more difficult. Too light will cause the oil film to brake in high revs high temp, destroying the engine, even if you still see a 5 in the gauge.
Any problem bleeding oil back to the pan is unimportant as long as pressure builds up quick to 5 with revs, as it's exactly the same thing the max pressure valve does all the time. The real important thing is having a proper oil temp (below 130º hot, easy with an unexpensive thermocouple or any other old temp sensor) and a proper oil weight for that temp (50).
07-02-2007, 03:22 PM
#34
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Originally Posted by ErnestSw
Just started the car dead cold and the needle swings right up to the 5 bar mark with a slightly slower rate of rise to about 1 bar and a very rapid rise to 5 bar. The time to reach 5 bar is about one second.
Since you indicate that you also see the low pressure warning light in addition to low pressure indicated on the gauge I'd say the sender is also low on the list of culprits.
Do you hear any evidence of low pressure? Like lifters getting noisy?
Does your oil pan gasket leak? If no to the former and yes to the latter then the first thing I would do is clean the harness connector to the sender.
Oh, and see Andrews thread on using the digi dash to get a digital readout of the pressure.
07-02-2007, 04:35 PM
#35
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So just for grins, one might want to take a look in the owner's manual. That's the book that came in the glovebox that nobody reads. Well, a few of us do. Take a look at yours and see if you can see where any 5W- oils are suitable for 90 degree ambient.
The 5W- part of the oil grade is what indicates the viscosity and therefore helps determine the hot oil pressure. The second number is a comparative film-strength value at 100C. eg: a 5W-40 at 100c (212F) has a hot film strength similar to a straight 40 weight oil at 100C. A 5w-40 is no thicker than a 5W-30, for practical purposes. 5W- may be fine for colder weather when you need that extra cold oil flow. But our cars were spec'd for 20W- in summer temps. I use 15W- Mobil-1 and it seems OK in the mild S. California climate. When I first got the car I was not that comfortable with 15W- since the book calls for 20W-, but there's enough overlap on the ranges to make this OK. The gauge still reads fine (2+) at hot idle so no worries, and it is 5bar well before 2000 RPM.
The US Delvac is not the same as the stuff that Doug was using in his car down under. RTFM for a viscosity suitable to the conditions in which you operate your car. Buy the best oil you can in that viscosity. Do that, and call me iin the morninig if the condition persists.
The 5W- part of the oil grade is what indicates the viscosity and therefore helps determine the hot oil pressure. The second number is a comparative film-strength value at 100C. eg: a 5W-40 at 100c (212F) has a hot film strength similar to a straight 40 weight oil at 100C. A 5w-40 is no thicker than a 5W-30, for practical purposes. 5W- may be fine for colder weather when you need that extra cold oil flow. But our cars were spec'd for 20W- in summer temps. I use 15W- Mobil-1 and it seems OK in the mild S. California climate. When I first got the car I was not that comfortable with 15W- since the book calls for 20W-, but there's enough overlap on the ranges to make this OK. The gauge still reads fine (2+) at hot idle so no worries, and it is 5bar well before 2000 RPM.
The US Delvac is not the same as the stuff that Doug was using in his car down under. RTFM for a viscosity suitable to the conditions in which you operate your car. Buy the best oil you can in that viscosity. Do that, and call me iin the morninig if the condition persists.
07-02-2007, 07:16 PM
#36
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I've been corrected some by oil guru Doug Hillary. We disagree on some things but I bow to his experience and knowledge. Thanks for the clinic, Doug!
----
There is a 5W- allowance in my owner's manual for "fuel saving" oil formulations. In the "multi-grade" category, 15W-40 to 20W-50 seem to cover the warmer-temp operating requirements. In my limited experience with both air/oil-cooled 356 and 911 cars, and water-cooled cars of various flavors and vintages, selecting an oil is a function of maintaining adequate oil pressure first, then maintaining adequate oil cooling next. Thicker oils may not carry heat out as well, and also may have cold-flow problems on initial start-up. Bottom line, in my experience, is to run the thinnest oil you can while maintaining adequate oil pressure. If a 5W- or even a 0W- oil will do that, in your car and with your driving conditions, it would be a better choice than a 15W- or 20W- oil. The factory allows for straight 40 weight oil for ambients above about 25c, if you were forced to choose a single-weight oil. Probably not the best choice overall though since you do have to start the car.
15W-50 M1 has been fine in my particular 928, following an early life bathed in 20W-50 Castrol GTX from the previous owner. Kibort bad-mouths Mobil-1 but it's been fine for me. He likes the thicker Amsoil, and may have a good point if it foams less. Aerated oil breaks the siphon that feeds the rod bearings, so a low-foam oil can be a life-saver in a high-RPM engine. For the sub-4000 RPM crowd of drivers like me, darn near anything would be adequate though.
Does anybody remember running straight 40 or 50 weight oil in roller-bearing 356 and 912 engines? Straight 60 weight non-detergent in older Harley's even though they had an external defoaming oil tank? At least on the Harley, the thicker stuff helped with the piston clearances as well as the slave rod bearing clearances.
YMMV, depending out your contact patch!
----
There is a 5W- allowance in my owner's manual for "fuel saving" oil formulations. In the "multi-grade" category, 15W-40 to 20W-50 seem to cover the warmer-temp operating requirements. In my limited experience with both air/oil-cooled 356 and 911 cars, and water-cooled cars of various flavors and vintages, selecting an oil is a function of maintaining adequate oil pressure first, then maintaining adequate oil cooling next. Thicker oils may not carry heat out as well, and also may have cold-flow problems on initial start-up. Bottom line, in my experience, is to run the thinnest oil you can while maintaining adequate oil pressure. If a 5W- or even a 0W- oil will do that, in your car and with your driving conditions, it would be a better choice than a 15W- or 20W- oil. The factory allows for straight 40 weight oil for ambients above about 25c, if you were forced to choose a single-weight oil. Probably not the best choice overall though since you do have to start the car.
15W-50 M1 has been fine in my particular 928, following an early life bathed in 20W-50 Castrol GTX from the previous owner. Kibort bad-mouths Mobil-1 but it's been fine for me. He likes the thicker Amsoil, and may have a good point if it foams less. Aerated oil breaks the siphon that feeds the rod bearings, so a low-foam oil can be a life-saver in a high-RPM engine. For the sub-4000 RPM crowd of drivers like me, darn near anything would be adequate though.
Does anybody remember running straight 40 or 50 weight oil in roller-bearing 356 and 912 engines? Straight 60 weight non-detergent in older Harley's even though they had an external defoaming oil tank? At least on the Harley, the thicker stuff helped with the piston clearances as well as the slave rod bearing clearances.
YMMV, depending out your contact patch!
07-02-2007, 08:55 PM
#37
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Dave,
I don't have any oil leaks and I haven't noticed any lifter noise, but my sample is very small (about 5 occasions one day and haven't driven the car since).
I don't have any oil leaks and I haven't noticed any lifter noise, but my sample is very small (about 5 occasions one day and haven't driven the car since).
07-02-2007, 09:42 PM
#39
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Anyone got any thoughts on Penrite 10W70??
I got quite a shock after putting this oil in the engine, and then at the same time, started seeing all these posts on (low oil pressure issues, and thrust bearing failures). I ignored half of these posts.
After this oil was put in, the oil pressure came up by at least 1bar at idle, climbs to 5bar before 2000RPM and stays there, and the engine is so much quieter in running.
Previously had Mobil 1, but I'm unsure of the grade. It's definately flowing more oil through the engine with this Penrite stuff!
What are peoples thoughts?
Glenn
'81 9-2-8
I got quite a shock after putting this oil in the engine, and then at the same time, started seeing all these posts on (low oil pressure issues, and thrust bearing failures). I ignored half of these posts.
After this oil was put in, the oil pressure came up by at least 1bar at idle, climbs to 5bar before 2000RPM and stays there, and the engine is so much quieter in running.
Previously had Mobil 1, but I'm unsure of the grade. It's definately flowing more oil through the engine with this Penrite stuff!
What are peoples thoughts?
Glenn
'81 9-2-8
