2015 Z51 Oil pressure low
10-11-2017, 10:00 PM
#2
Completely normal. The LT1 (and LT4) engines have dual displacement oil pumps and full pump capability is only used under high RPM/high stress conditions.
If you watch closely a short time after startup (usually 3 to 5 minutes) you will see the oil pressure increase rapidly several times in succession and this is the dual displacement pump testing itself. If the controller fails the pump defaults to high flow mode for safety.
If you watch closely a short time after startup (usually 3 to 5 minutes) you will see the oil pressure increase rapidly several times in succession and this is the dual displacement pump testing itself. If the controller fails the pump defaults to high flow mode for safety.
10-11-2017, 10:03 PM
#3
The Consigliere
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Long-standing rule of thumb is 10 pounds per 1k rpm is sufficient minimum for lower rpms - below that, time to take it apart.
10-12-2017, 05:16 AM
#4
E-Ray, 3LZ, ZER, LIFT
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As mentioned, the LT1/4 has a "Variable Volume" oil pump. Like many our things, the computer controls when more volume is needed. When it switches to lower volume, pressure decreases. GM and other manufactures are using every opportunity to improve their corporate MPG fleet number!
For those who want to know how it works, pic below it what the computer changes. That are probably using throttle position, engine vacuum and other inputs. not just rpm to define when the high volume is needed.
By moving the outer pump race using a solenoid, the volume delivered by the oil pump varies. The siding vanes, shown in alternate position in red, show how the volume changes. The pump center is driven from the crank nose. A solenoid pushrod, inside the spring, controls the position as determined by a computer.
Last edited by JerryU; 10-12-2017 at 05:28 AM.
10-12-2017, 11:22 AM
#5
The Consigliere
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I don't think that affects the minimum amount of pressure to protect internals one wants as a floor minimum for lower rpms.
For example, if you have less than 10 pounds pressure at 1k rpm - even with the new pump style, then it's time to take the engine apart.
As I understand it the new pump operation, it moderates the pressure at higher rpms, but maintains pressure at lower rpms that we're accustomed to seeing.
For example, if you have less than 10 pounds pressure at 1k rpm - even with the new pump style, then it's time to take the engine apart.
As I understand it the new pump operation, it moderates the pressure at higher rpms, but maintains pressure at lower rpms that we're accustomed to seeing.
Last edited by OnPoint; 10-12-2017 at 11:29 AM.
10-12-2017, 02:52 PM
#6
E-Ray, 3LZ, ZER, LIFT
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I don't think that affects the minimum amount of pressure to protect internals one wants as a floor minimum for lower rpms.
For example, if you have less than 10 pounds pressure at 1k rpm - even with the new pump style, then it's time to take the engine apart.
As I understand it the new pump operation, it moderates the pressure at higher rpms, but maintains pressure at lower rpms that we're accustomed to seeing.
For example, if you have less than 10 pounds pressure at 1k rpm - even with the new pump style, then it's time to take the engine apart.
As I understand it the new pump operation, it moderates the pressure at higher rpms, but maintains pressure at lower rpms that we're accustomed to seeing.
In fact there was an interesting recent GM bulletin re the pressure release valve value in the GM specified oil filter being a lower pressure! One reason I only use the recommended oil filter.
A replacement "equivalent" filter may not be as low! It could bypass the filter at pressures the recommended filter will not. It mentions with the use of variable volume pumps this specifican has changed.
Need to be careful with the higher pressure capable "racing" version some folks use!
VOLUME VS PRESSURE: As far as moderating pressure at high rpm they could have done that with simple pressure relief valve spring that has been used for years. This new system actually varies pump volume controlled by the computer and the resulting observed pressure drop is a result.
I initially thought myself that the solienoid was just opening another passage in the normal pump bypass circuit (that the new system still retains.) But if you examine the figure I posted, you'll see it actually changes the pump configuration to reduce the oil volume pumped! That reduces the energy used by the pump more than a pressure relieve bypass system that still pumps the same volume of oil though the pump itself.
Last edited by JerryU; 10-12-2017 at 02:59 PM.
10-12-2017, 04:05 PM
#7
A lot of newer engines, including the LT1 and LT4, rely heavily upon the "piston oil squirters" to cool the pistons under extreme operating conditions and this requires significant oil volume. If GM wasn't using a variable displacement oil pump the energy required to operate a fixed displacement pump sufficient to supply extreme condition needs would have an impact upon economy and given ever more stringent CAFE standards that wasn't acceptable.
At the other extreme GM had to issue a bulletin over customer concerns about high oil pressure with their latest generation L5P Duramax diesel. At cold start it will usually pin the 120 PSI gauge until the oil warms up and this is the type of flow and pressure you get with a fixed displacement pump sufficient to supply the much needed piston coolers and other lube circuit requirements in a turbo-diesel engine that also has a relatively low operating RPM (governed at 3450 under load with torque peak of 915 pound feet at 1,600 RPM and the horsepower peak of 445 occurring at 2,800). CAFE isn't yet an issue for the heavy duty segment.
At the other extreme GM had to issue a bulletin over customer concerns about high oil pressure with their latest generation L5P Duramax diesel. At cold start it will usually pin the 120 PSI gauge until the oil warms up and this is the type of flow and pressure you get with a fixed displacement pump sufficient to supply the much needed piston coolers and other lube circuit requirements in a turbo-diesel engine that also has a relatively low operating RPM (governed at 3450 under load with torque peak of 915 pound feet at 1,600 RPM and the horsepower peak of 445 occurring at 2,800). CAFE isn't yet an issue for the heavy duty segment.
Last edited by NSC5; 10-12-2017 at 04:07 PM.
10-12-2017, 04:39 PM
#8
The Consigliere
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It actually lowers the pressure even at lower rpm than in my C6 when just cruising.
In fact there was an interesting recent GM bulletin re the pressure release valve value in the GM specified oil filter being a lower pressure! One reason I only use the recommended oil filter.
A replacement "equivalent" filter may not be as low! It could bypass the filter at pressures the recommended filter will not. It mentions with the use of variable volume pumps this specifican has changed.
Need to be careful with the higher pressure capable "racing" version some folks use!
VOLUME VS PRESSURE: As far as moderating pressure at high rpm they could have done that with simple pressure relief valve spring that has been used for years. This new system actually varies pump volume controlled by the computer and the resulting observed pressure drop is a result.
I initially thought myself that the solienoid was just opening another passage in the normal pump bypass circuit (that the new system still retains.) But if you examine the figure I posted, you'll see it actually changes the pump configuration to reduce the oil volume pumped! That reduces the energy used by the pump more than a pressure relieve bypass system that still pumps the same volume of oil though the pump itself.
In fact there was an interesting recent GM bulletin re the pressure release valve value in the GM specified oil filter being a lower pressure! One reason I only use the recommended oil filter.
A replacement "equivalent" filter may not be as low! It could bypass the filter at pressures the recommended filter will not. It mentions with the use of variable volume pumps this specifican has changed.
Need to be careful with the higher pressure capable "racing" version some folks use!
VOLUME VS PRESSURE: As far as moderating pressure at high rpm they could have done that with simple pressure relief valve spring that has been used for years. This new system actually varies pump volume controlled by the computer and the resulting observed pressure drop is a result.
I initially thought myself that the solienoid was just opening another passage in the normal pump bypass circuit (that the new system still retains.) But if you examine the figure I posted, you'll see it actually changes the pump configuration to reduce the oil volume pumped! That reduces the energy used by the pump more than a pressure relieve bypass system that still pumps the same volume of oil though the pump itself.
So something less than 10 pounds at 1k rpm is now regarded as a safe floor minimum of pressure?
10-12-2017, 08:23 PM
#9
E-Ray, 3LZ, ZER, LIFT
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^^^
Not at all, as you said if the car reads 10 psi @ 1000 rpm, probably need and overhaul! Would hope since GM has the system measuring a number of variables and no doubt oil pressure being one they would send a warning if the pressure gets too low.
I recall the low pressure release valve value mentioned in the GM bulletin re oil filters was ~15 psi or lower. (Currently in California for two weeks so no access to the doc I saved.) I have never seen anything lower than high 20's in my 2014 Z51 or my Grand Sport!
I was just commenting on your "old rule of thumb" of x psi/rpm. It's no longer true.
Not at all, as you said if the car reads 10 psi @ 1000 rpm, probably need and overhaul! Would hope since GM has the system measuring a number of variables and no doubt oil pressure being one they would send a warning if the pressure gets too low.
I recall the low pressure release valve value mentioned in the GM bulletin re oil filters was ~15 psi or lower. (Currently in California for two weeks so no access to the doc I saved.) I have never seen anything lower than high 20's in my 2014 Z51 or my Grand Sport!
I was just commenting on your "old rule of thumb" of x psi/rpm. It's no longer true.
Last edited by JerryU; 10-12-2017 at 09:58 PM.
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10-13-2017, 04:53 PM
#10
Burning Brakes
As others have stated, the C7 will test system as you drive down the road. When I first got my C7, thought about low oil pressure, the one day I looked down and saw the system test itself, pressure went up to 60, then down a bit & back up 60psi, then back down to the normal system pressure. Dang computers, do everything now.