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Interpreting oil pressure vs engine RPM #4106686 05/25/16 08:39 PM
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Emperors6 Offline OP
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Hi,

I was wondering if I could some help determining if I chose the correct oil for my summer application. I have switched to Redline 5W30 for the summer (due to track days mostly).

I'm working on my logging setup, but here's some graphs from a 500mile (mostly highway trip). It doesn't look like I meet the 1000rpm/10psi "rule." Any advice?




2013 Cadillac CTS-V
2016 Chevrolet Corvette Z06
Re: Interpreting oil pressure vs engine RPM [Re: Emperors6] #4106697 05/25/16 08:50 PM
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eljefino Offline
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It's "at least" that pressure. You're fine.

Neverminding that where the pressure is tested varies widely and only speaks for that one corner of the engine.

Re: Interpreting oil pressure vs engine RPM [Re: eljefino] #4106709 05/25/16 09:08 PM
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abycat Offline
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Originally Posted By: eljefino
It's "at least" that pressure. You're fine.

Neverminding that where the pressure is tested varies widely and only speaks for that one corner of the engine.


+2 smile


2017 dodge caravan gt
2011 nissan versa hb
Re: Interpreting oil pressure vs engine RPM [Re: Emperors6] #4106787 05/25/16 10:22 PM
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yvon_la Offline
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oil would be too thick for the temperature you are in


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Nissan versa note s 2014 total classic 5w30(qc.ca) drivework oil filter
Re: Interpreting oil pressure vs engine RPM [Re: Emperors6] #4106839 05/25/16 11:55 PM
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BrocLuno Offline
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That "rule" is not applicable to all engines. It was developed in the 50's for early mass production push-rod motors.

You need enough oil pressure to get oil to where it needs to be, plus some margin for temp spikes and such. Some motors will live with 10 psi at 5,000 rpm. Some motors will want close to 50 at the same RPM. Oil pump volume vs bearing leakage/sling will mean way more than just an arbitrary number and some rule of thumb...

Don't know the motor in question, but take a Chevy Big Block. You can can tap a plug along the side of the block for the gallery at the back of the crank and one at the front. If the gauges read close to the same at both ends, you are good to go. But if you have >15 psi differential with 50 psi feed at the filter, you'll loose a bearing at high rpm...

You need to know if enough oil is getting to vital areas?

Last edited by BrocLuno; 05/26/16 12:01 AM.

Formerly in marine engineering. In an earlier life I owned my own petroleum tank truck, and hauled for the majors and independent's.
Re: Interpreting oil pressure vs engine RPM [Re: Emperors6] #4106840 05/25/16 11:58 PM
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alcyon Offline
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pressure seems low to me.


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Re: Interpreting oil pressure vs engine RPM [Re: Emperors6] #4106897 05/26/16 04:51 AM
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bobbydavro Offline
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Where is the pressure sensor?

Re: Interpreting oil pressure vs engine RPM [Re: Emperors6] #4106931 05/26/16 06:37 AM
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Shannow Offline
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Wondering why you are trying to determine if you have the correct viscosity by pressure versus RPM ?

As BrocLuno states, the "rule" was basically developed for the American Small Block.

Pressure in the oil galleries is due to the oil pump providing more oil than the bearings can draw from the galleries...there has to be enough pressure that gets all of the required oil TO the bearings, but as bobbydavro asks, where is the pressure taken ?

And finally, while oil pressure IS related to viscosity, the oil pressure doesn't tell you what's happening in locations like the big end.

Your OEM provides a minimum oil pressure recommendation as a maintenance intervention point for a worn engine on the recommended oil viscosity...others on BITOG who have literally zero understanding of hydrodynamic lubrication (flow equals lubrication in their world) have taken that minimum oil pressure as a target for viscosity choice...the fact that they get away with it does not make it optimum.

Re: Interpreting oil pressure vs engine RPM [Re: Emperors6] #4106939 05/26/16 06:52 AM
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A_Harman Offline
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Redline 5w30 should be a fine oil for your CTS-V. But the data you have logged while driving on the highway at 1500 rpm average engine speed won't be representative of what you get on track. Running the engine between 4000-6000 rpm for 20-30 minutes during a lapping session will get the oil up to 280F+. Then the oil pressure will drop significantly.

Don't worry very much about the average oil pressure while running down the straights, worry about the minimum oil pressure while running through long turns at high lateral G's. Long left-hand turns in my Corvette lead to oil pressures of <20psi. Does your datalogger also record G's?

Last edited by A_Harman; 05/26/16 06:54 AM.

1985 Z51 Corvette track car
2002 Camaro Z28 LS1/6-speed
2001 Dodge Ram 2500 diesel
1972 GMC 1500 shortbed project truck
Re: Interpreting oil pressure vs engine RPM [Re: bobbydavro] #4106960 05/26/16 07:24 AM
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Emperors6 Offline OP
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Thanks for everyone's replies so far!

Originally Posted By: bobbydavro
Where is the pressure sensor?

No idea, I'm using an OBD-II reader to poll a PID that claims to be the oil pressure.

Originally Posted By: Shannow
Wondering why you are trying to determine if you have the correct viscosity by pressure versus RPM ?

I want to make sure the oil is not too thick (due to its higher HTHS value compared to other 5W30s).

Originally Posted By: Shannow
Your OEM provides a minimum oil pressure recommendation as a maintenance intervention point for a worn engine on the recommended oil viscosity...

According to the engine spec , the minimum hot pressure are 6 psig @ 1000 RPM, 18 psig @ 2000 RPM, 24 psig @ 4000 RPM. Is the gauge giving me psig or psi so I can do a direct comparison?

Originally Posted By: Shannow
...others on BITOG who have literally zero understanding of hydrodynamic lubrication (flow equals lubrication in their world) have taken that minimum oil pressure as a target for viscosity choice...the fact that they get away with it does not make it optimum.

So, what should I be targeting then if not as a minimum?

Originally Posted By: A_Harman
Don't worry very much about the average oil pressure while running down the straights, worry about the minimum oil pressure while running through long turns at high lateral G's. Long left-hand turns in my Corvette lead to oil pressures of <20psi. Does your datalogger also record G's?

I need to take a look at the log for the track session that I ran it the hardest. I'm working on doing some summary graphs automatically for any trip data and then I can quickly eyeball rather processing them manually, which is what I'm doing now.
I use Torque Pro, and it does have a setting to log acceleration. I guessing I want a field called G(calibrated) and not G(x), G(y), G(z).


2013 Cadillac CTS-V
2016 Chevrolet Corvette Z06
Re: Interpreting oil pressure vs engine RPM [Re: BrocLuno] #4106964 05/26/16 07:29 AM
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Emperors6 Offline OP
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Originally Posted By: BrocLuno

Don't know the motor in question, but take a Chevy Big Block. You can can tap a plug along the side of the block for the gallery at the back of the crank and one at the front. If the gauges read close to the same at both ends, you are good to go. But if you have >15 psi differential with 50 psi feed at the filter, you'll loose a bearing at high rpm...

You need to know if enough oil is getting to vital areas?


I don't have any mechanical experience to starting modifying anything. Right now, I just want to see based on what readings I can pull if the values make sense. Besides, how would I do what you describe? My general understanding is that the coolant is run through the engine so the oil flow is all internal to the engine or is the oil run outside the engine so there's somewhere I can tap the flow?


2013 Cadillac CTS-V
2016 Chevrolet Corvette Z06
Re: Interpreting oil pressure vs engine RPM [Re: Emperors6] #4106966 05/26/16 07:33 AM
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Shannow Offline
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Originally Posted By: Emperors6
According to the engine spec , the minimum hot pressure are 6 psig @ 1000 RPM, 18 psig @ 2000 RPM, 24 psig @ 4000 RPM. Is the gauge giving me psig or psi so I can do a direct comparison?

Originally Posted By: Shannow
...others on BITOG who have literally zero understanding of hydrodynamic lubrication (flow equals lubrication in their world) have taken that minimum oil pressure as a target for viscosity choice...the fact that they get away with it does not make it optimum.

So, what should I be targeting then if not as a minimum?


Nice donk (Aussie slang for engine)...really nice.

Again, they are offering a maintenance minimum oil pressure, not a target oil pressure.

They offer M1 5W30 an ILSAC 3.1 HTHS oil as their benchmark.

So if you run M1 5W30 and hit any of those triggers as the engine wears, you need to take action.

If you have a new engine, that does not mean target your viscosity to reach that oil pressure.

Re: Interpreting oil pressure vs engine RPM [Re: Shannow] #4106971 05/26/16 07:43 AM
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Emperors6 Offline OP
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Originally Posted By: Shannow


Nice donk (Aussie slang for engine)...really nice.

Again, they are offering a maintenance minimum oil pressure, not a target oil pressure.

They offer M1 5W30 an ILSAC 3.1 HTHS oil as their benchmark.

So if you run M1 5W30 and hit any of those triggers as the engine wears, you need to take action.

If you have a new engine, that does not mean target your viscosity to reach that oil pressure.


I see, I'll keep that in mind as the engine wears. It's about 2 years old with about 35k miles (85%+ highway use), so I don't think I'll worry about that for a while.

I was planning on running Redline 0W30 in the winter since it might be sitting outside in -15C to -20C weather from time to time and I want to reduce any startup wear. Granted, that will maybe be only a month out of the year as it's usually warmer than that, so I want to make sure this thinner oil with HTHS 3.2 isn't a bad idea. Obviously, I won't be tracking it with this oil due to the weather. Thoughts?


2013 Cadillac CTS-V
2016 Chevrolet Corvette Z06
Re: Interpreting oil pressure vs engine RPM [Re: Emperors6] #4106972 05/26/16 07:44 AM
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A_Harman Offline
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Originally Posted By: Emperors6
Thanks for everyone's replies so far!



Originally Posted By: Shannow
Wondering why you are trying to determine if you have the correct viscosity by pressure versus RPM ?

I want to make sure the oil is not too thick (due to its higher HTHS value compared to other 5W30s).

Originally Posted By: A_Harman
Don't worry very much about the average oil pressure while running down the straights, worry about the minimum oil pressure while running through long turns at high lateral G's. Long left-hand turns in my Corvette lead to oil pressures of <20psi. Does your datalogger also record G's?

I need to take a look at the log for the track session that I ran it the hardest. I'm working on doing some summary graphs automatically for any trip data and then I can quickly eyeball rather processing them manually, which is what I'm doing now.
I use Torque Pro, and it does have a setting to log acceleration. I guessing I want a field called G(calibrated) and not G(x), G(y), G(z).



I don't know how the Torque Pro programming goes, but I'm guessing that G(x) is for longitudinal acceleration (gas & brake), G(y) is lateral (left turn, right turn), G(z) is for vertical, and G(calibrated) is the vector sum of all three. Acceleration G's should be pretty low, .2-.3 G's at the higher speeds. Braking and Turning G's should be up around 1.0 if you're driving hard. If you can plot G's and oil pressure vs. time, that would show you what the oil pressure is when you're going around turns.


1985 Z51 Corvette track car
2002 Camaro Z28 LS1/6-speed
2001 Dodge Ram 2500 diesel
1972 GMC 1500 shortbed project truck
Re: Interpreting oil pressure vs engine RPM [Re: Emperors6] #4106977 05/26/16 07:48 AM
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Shannow Offline
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Originally Posted By: Emperors6
I was planning on running Redline 0W30 in the winter since it might be sitting outside in -15C to -20C weather from time to time and I want to reduce any startup wear. Granted, that will maybe be only a month out of the year as it's usually warmer than that, so I want to make sure this thinner oil with HTHS 3.2 isn't a bad idea. Obviously, I won't be tracking it with this oil due to the weather. Thoughts?


I don't believe that you need 0W anything to reduce start-up wear over a 5W at -15 to -20C...if you were talking -30C, then probably.

The recommended oil per your OEM data sheet has an HTHS of around 3.1 anyway.

If you like Redline, and you seem to, just use the 0W30 all year round. Otherwise, M1 5W30.

I really don't think that there's a material difference in how these will protect.

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