But then it decreases as the heat from the load thins the oil .No?
How to Determine the Correct Oil Grade for your Car
- Thread starter AEHaas
- Start date
"more time to pick up the hear" ... Typo ??
The amount of time it takes for the oil to flow through a defined passage is dependent on the passage volume and the volume output of the PD pump (which is RPM dependent).
Welcome back. Read many of your posts through the years along with your findings on oil LONG before I joined this forum. It's because of you I decided to get into more in depth oil related information. Looking forward to your posts. Cheers.
Just tell us the truth - you wanna use that Magnatec 5w20 you’ve got on sale right?
Honestly, I’m glad that you have that kind of problem when approaching the retirement.
Beat me to it ...Except when it comes to computer controlled variable output oil pumps.
RE: 10 psi / 1K rpm
My oil pressure gauge has no psi numbers which bugs me and I recently saw someone posted a picture of my truck service manual and i remember at 3000 rpm the oil pressure was supposed to be 45-60 psi.
I will double check, however I don't think 10PSI per 1000RPM can be a universal figure ... besides that, with many different engine designs and applications, it would be hard to believe they could all follow the same 10/1K rule.
Edit:
Just double checked:
RPM vs. Oil pressure:
V6 @3000 RPM: 36-75 PSI
V8 @3000 RPM: 43-85 PSI (picture is a little out of focus. I think it's 85 and not 65). Either way it's much more than 10psi per 1000rpm.
My oil pressure gauge has no psi numbers which bugs me and I recently saw someone posted a picture of my truck service manual and i remember at 3000 rpm the oil pressure was supposed to be 45-60 psi.
I will double check, however I don't think 10PSI per 1000RPM can be a universal figure ... besides that, with many different engine designs and applications, it would be hard to believe they could all follow the same 10/1K rule.
Edit:
Just double checked:
RPM vs. Oil pressure:
V6 @3000 RPM: 36-75 PSI
V8 @3000 RPM: 43-85 PSI (picture is a little out of focus. I think it's 85 and not 65). Either way it's much more than 10psi per 1000rpm.
Last edited:
Welcome Back Doc !
10 Psi per 1k rpm has been the standard for the last 60 or 70 years. With today's modern designs, I'm not so sure.
Oil pressure is just a supply of oil to the bearings...to make up for the leakage out the side.
THe oil passign through bearings doesn't "cool" the bearings, the heat within the bearings is generated bythe shearing that takes place across the oil film, generating heat.
The thicker oil will always have a greater MOFT, and typically run hotter.
The thinner oil does not "cool" the bearing more effectively, it just makes less heat, has greater side leakage, and needs moer flow to make up for it.
Right.... Caterham wrote that increasing the oil pressure would compensate for a thinner oil. Eventually he would give it up, take a long vacation, then return with the same nonsense. On occation, he would acost or plant a new member to do his bidding.
Edit; In short, you can't use an oil pressure guage to determine the correct engine oil viscosity for a specific application.
Interesting. Then why monitor oil pressure at all?
On page 154 of my old Ferrari 575M the manual says this: "In standard operating conditions, oil pressure must be between 5 and 6bar with the engine operating at 6,000 rpm and oil temperature at 212 °F (100 °C)." This is 72-87 PSI, not less, not more. So Ferrari thinks the actual oil pressure is important.
They also say to use either 0-40 or 5-40 oil except for racing conditions where they recommend a 60 grade oil. Once again, the proper grade for the application/conditions/load/oil temperatures.
AEHaas
- Joined
- Jul 11, 2014
- Messages
- 4,117
Engines will have different requirements. Sorry, I never believed in the any general rule of 10psi per 1000 rpm.
Liking the new variable oil pumps.... make a big pump at low RPM and then switch to smaller pump as RPM is increased and reduce waste oil flow via a pump bypass. Glad it was mentioned already.
And, there is oil temp control, better controlled with newer vehicles with heater/coolers....
I don't want 10psi per 1000 RPM.... I want 80psi from idle to redline. Yeah, thats the ticket.
Liking the new variable oil pumps.... make a big pump at low RPM and then switch to smaller pump as RPM is increased and reduce waste oil flow via a pump bypass. Glad it was mentioned already.
And, there is oil temp control, better controlled with newer vehicles with heater/coolers....
I don't want 10psi per 1000 RPM.... I want 80psi from idle to redline. Yeah, thats the ticket.
Oil pressure is important because without it "Houston we have a problem".
For the furthest bearing, wrist pin, lifter or rocker from the pressure gauge to recieve a sufficient supply of oil, which increases with rpm,
the pressure at the gauge mut be X.
As long as there is a supply of oil to the bearings, they will "self pump". Not so much for the valve train which needs force feeding.
Oil thins from heating. RPM causes the oil to heat more than other factors. That can be proven by motoring an engine that is not running.
Engine load is the factor that causes the water in the cooling system to heat.
If your engine has an oil pressure too low at any rpm to supply the needs of the engine, cam lobes will wipe out and engine bearings will
squeek to a stop.
One member posted "Why live on the ragged edge?" Others post "I use XW-HTHS and it hasn't blown up yet."
Yep, but wait for the engine to wear a little, the side leakage from the bearings increase and you will get your wish.
So we monotor oil pressure. If it ain't what it used to be, go thicker.
Going to a bigger oil pump to maintain pressure is one approach as long as the oil is thick enough to keep the hydrodynamically
lubricated parts separated and other engine parts in their intended lubricating regemes. (boundary etc)
Oil pressure specs like noted in the manual is basically a "health check" of the engine oiling system operation - as well as the condition of the oil clearances in the bearings, etc throughout the oiling system. Each engine with the called out specified oil is going to be unique. In your case it calls out oil pressure of 72-87 PSI at 6000 RPM with the specified oil (assuming xW-40) at 100 C.
What's the oil pressure at idle with the oil at 100 C with the specified xW-40 oil ?
What is the oil pressure at idle with the oil at 100 C with the xW-20 oil you are using ?
What is the oil pressure at 6000 RPM with the oil at 100 C with the xW-20 oil you are using ?
Last edited:
Where are all the engines that wore and then blew up running 0w20?
Primary factors for determining oil viscosity...
- Oil temperature
- Rod and main bearing clearance
- Load on those bearings
Secondary factors for determining oil viscosity...
- Ring tension and thickness
- Piston speed
- Hydraulic lifter pump-up/bleed
NHRA Pro Stock, NASCAR Cup Series, and WoO Sprints all have similar rod and main bearing clearances but use 0w-8, 0w-20, and 5w-50 respectively because of differences in load and temperature.
- Oil temperature
- Rod and main bearing clearance
- Load on those bearings
Secondary factors for determining oil viscosity...
- Ring tension and thickness
- Piston speed
- Hydraulic lifter pump-up/bleed
NHRA Pro Stock, NASCAR Cup Series, and WoO Sprints all have similar rod and main bearing clearances but use 0w-8, 0w-20, and 5w-50 respectively because of differences in load and temperature.
Similar threads
