The by-pass value basically caps the maximum back-pressure at a certain level. Assuming your oil pressure gauge functions normally; not pegged for example, then the maximum OP reading should be the by-pass point.
Thicker vs. Thinner and oil temps.
- Thread starter chubbs1
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I have seen variations (5 psi or so) in the maximum OP gauge readings on the same engine and make and model of car.
I don't know what to attribute it to other than possible variations in the calibration of the gauge itself and/or the by-pass valve spring rate.
I don't know what to attribute it to other than possible variations in the calibration of the gauge itself and/or the by-pass valve spring rate.
The pressure-relief valve for the oil pump will begin to open (crack) at a certain pressure and will continue to bypass more flow as pressure rises until it is completely open. Different engines have different pump & valve designs so they will behave differently.
In general, the oil pressure will rise with rpm at a linear rate as long as the valve is closed. After the valve cracks-open, the rate will begin to taper-off and should eventually flatline. Some pumps can over-flow the bypass at high rpm (or with high-viscosity oil) and end up with pressures beyond the designed max rating.
In general, the oil pressure will rise with rpm at a linear rate as long as the valve is closed. After the valve cracks-open, the rate will begin to taper-off and should eventually flatline. Some pumps can over-flow the bypass at high rpm (or with high-viscosity oil) and end up with pressures beyond the designed max rating.
For those that want actual data related to flow and viscosity, you may want to consider having a look at the paper linked below. This paper is primarily based on a Vicker vane pumps to confirm an earlier paper that described gear pumps (I don't have a link to the gear-pump paper). The higher the viscosity, the higher the pump output at a fixed RPM. As described earlier, the source of flow loss is related to pick-up plumbing inefficiencies and leakage. Otherwise, as viscosity increases, flow INCREASES. In practice, as pressure increases, leakage increases an as a vapor pressure differential is increased, cavitation increases.
http://www.mehf.com/isfl02pumpeffpaper.pdf
http://www.mehf.com/isfl02pumpeffpaper.pdf
Here is another paper related to pump efficiency and viscosity that includes shear stability of VIIs:
http://www.mehf.com/IFPE05MEHFFlowStability.pdf
http://www.mehf.com/IFPE05MEHFFlowStability.pdf
I found a related discussion that may entertain a few of you:
http://www.eng-tips.com/viewthread.cfm?qid=33323
http://www.eng-tips.com/viewthread.cfm?qid=33323
I found this article interesting from this publication:
http://books.google.ca/books?id=VzWSJmvG...p;q&f=false
http://i.imgur.com/dKPhv.png
http://i.imgur.com/zQy4y.png
http://i.imgur.com/3JmZQ.png
http://books.google.ca/books?id=VzWSJmvG...p;q&f=false
http://i.imgur.com/dKPhv.png
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2nd try.
Originally Posted By: martinq
I found this article interesting from this publication:
http://books.google.ca/books?id=VzWSJmvG...p;q&f=false
http://i.imgur.com/6Ww6y.png
http://i.imgur.com/aaRSG.png
http://i.imgur.com/Iq78E.png
Originally Posted By: martinq
I found this article interesting from this publication:
http://books.google.ca/books?id=VzWSJmvG...p;q&f=false
http://i.imgur.com/6Ww6y.png
Originally Posted By: Jim Allen
That's what I had figured in my head but I was questioning my logic because the observed OP is so out of line with both of the conflicting bypass specs I was given.
Originally Posted By: CATERHAM
I have seen variations (5 psi or so) in the maximum OP gauge readings on the same engine and make and model of car.
I don't know what to attribute it to other than possible variations in the calibration of the gauge itself and/or the by-pass valve spring rate.
Electric oil pressure senders have lousy tolerances. Even when they start out accurate at the high end of the scale, they can drift way off as you move towards the other end. From what I've seen, every time you replace a sender they all read differently out of the box, on the same individual car. A mechanical gauge will wildly disagree with them.
When the real oil pressure is a serious concern, it's best to hook up a mechanical gauge to get a reliable reading. The dash gauge is useful to show general behavior but the numerical readings aren't trustworthy.
That's what I had figured in my head but I was questioning my logic because the observed OP is so out of line with both of the conflicting bypass specs I was given.
Originally Posted By: CATERHAM
I have seen variations (5 psi or so) in the maximum OP gauge readings on the same engine and make and model of car.
I don't know what to attribute it to other than possible variations in the calibration of the gauge itself and/or the by-pass valve spring rate.
Electric oil pressure senders have lousy tolerances. Even when they start out accurate at the high end of the scale, they can drift way off as you move towards the other end. From what I've seen, every time you replace a sender they all read differently out of the box, on the same individual car. A mechanical gauge will wildly disagree with them.
When the real oil pressure is a serious concern, it's best to hook up a mechanical gauge to get a reliable reading. The dash gauge is useful to show general behavior but the numerical readings aren't trustworthy.
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What's indisputable is that it makes no difference whether you're running a 20W-50 or a 0W-20 oil grade, nor does it make any difference what the VII content is of an oil, because for any given oil back-pressure reading below the oil pump by-pass point the operational viscosity and therefore the oil flow rates will be identical. Of course this will occur at a very much higher oil temperature with the heavier oil.
One should always select an oil that is viscous enough to provide adequate oil back-pressure under the normal hot operating conditions that will be encountered and that will be well below the by-pass setting of the oil pump at elevated rev's.
One should always select an oil that is viscous enough to provide adequate oil back-pressure under the normal hot operating conditions that will be encountered and that will be well below the by-pass setting of the oil pump at elevated rev's.
Originally Posted By: CATERHAM
What's indisputable is that it makes no difference whether you're running a 20W-50 or a 0W-20 oil grade, nor does it make any difference what the VII content is of an oil, because for any given oil back-pressure reading below the oil pump by-pass point the operational viscosity and therefore the oil flow rates will be identical. Of course this will occur at a very much higher oil temperature with the heavier oil.
I think you need to add RPM to that equation somewhere.
What's indisputable is that it makes no difference whether you're running a 20W-50 or a 0W-20 oil grade, nor does it make any difference what the VII content is of an oil, because for any given oil back-pressure reading below the oil pump by-pass point the operational viscosity and therefore the oil flow rates will be identical. Of course this will occur at a very much higher oil temperature with the heavier oil.
I think you need to add RPM to that equation somewhere.
Originally Posted By: supercity
Originally Posted By: CATERHAM
What's indisputable is that it makes no difference whether you're running a 20W-50 or a 0W-20 oil grade, nor does it make any difference what the VII content is of an oil, because for any given oil back-pressure reading below the oil pump by-pass point the operational viscosity and therefore the oil flow rates will be identical. Of course this will occur at a very much higher oil temperature with the heavier oil.
I think you need to add RPM to that equation somewhere.
Of course, you're always comparing at the same engine RPM.
Originally Posted By: CATERHAM
What's indisputable is that it makes no difference whether you're running a 20W-50 or a 0W-20 oil grade, nor does it make any difference what the VII content is of an oil, because for any given oil back-pressure reading below the oil pump by-pass point the operational viscosity and therefore the oil flow rates will be identical. Of course this will occur at a very much higher oil temperature with the heavier oil.
I think you need to add RPM to that equation somewhere.
Of course, you're always comparing at the same engine RPM.
i think a thinner oil both accepts heat and releases heat more quickly than a heavier oil, and flows faster so -> ideally the thinnest oil would be best for heat transfer and flow ala Dr. Haas - but wear becomes the problem
and it appears they are continually improving the oils to solve this problem
and it appears they are continually improving the oils to solve this problem
The key is to know how thin you can go before the onset of increased engine wear. In most applications today a 20wt oil will not produce any increased engine wear over a 30wt oil and s still have a substantial viscosity reserve for to deal with higher than normal oil temp's.
In a couple of years the Japanese OEMs will be specifying the new even lighter 0W-16 grade. It will be interesting to see how many models this new light oil will be spec'd for initially.
In a couple of years the Japanese OEMs will be specifying the new even lighter 0W-16 grade. It will be interesting to see how many models this new light oil will be spec'd for initially.
Of all of the methods that heat transfers, viscosity primarily affects convection. The thicker the oil, the less "mixing" of hot and cool regions that occurs and result in less heat removal by convection.
However, since the oil pump and moving parts ensures that mixing is continuous, this affect is primarily observed where oil pools, like the oil pan.
The primary factor for heat absorption by oil, given fixed flow rates, is the "wetting" ability of the oil. In other words, the better that the oil adheres to metal, the better the heat exchange. So, as polarity goes up, heat exchange goes up.
In practice, most petroleum based oils, will cool at about the same rate when flowing at the same rate. However, since heavy oils will require more work to maintain RPM at the pump, that energy is converted to heat and reduces the ability of the oil to remove more heat.
So, thinner oil cools better primarily because less heat is generated to pump it.
However, since the oil pump and moving parts ensures that mixing is continuous, this affect is primarily observed where oil pools, like the oil pan.
The primary factor for heat absorption by oil, given fixed flow rates, is the "wetting" ability of the oil. In other words, the better that the oil adheres to metal, the better the heat exchange. So, as polarity goes up, heat exchange goes up.
In practice, most petroleum based oils, will cool at about the same rate when flowing at the same rate. However, since heavy oils will require more work to maintain RPM at the pump, that energy is converted to heat and reduces the ability of the oil to remove more heat.
So, thinner oil cools better primarily because less heat is generated to pump it.
One thing I found interesting in that article was the excess of oil-pressure delivered to the engine by the oil pump. A variable pressure system would save the wasted power which is just putting heat into the oil and dragging on the engine.
And, 1 bar is about 14.5 psi.
So, are the general "rules of thumb" for oil pressure actually good recommendations? As RPM goes up, it does seem to become more important.
So, are the general "rules of thumb" for oil pressure actually good recommendations? As RPM goes up, it does seem to become more important.
According to that graph ^, an engine needs the same low pressure at 4,000 RPM as it does near idle.
I don't believe it at all.
I don't believe it at all.
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