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Is thicker synthetic run cooler?
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Originally Posted By: GMorg
I'm going to try again. The oil pump DOES NOT provide constant pressure at a given RPM. Positive displacement pumps provide constant flow at a fixed RPM (with the caveats described earlier). The pressure is higher at the pump and at the sending unit due to the resistance of the fluid to flow. The thicker the fluid, the more force that accumulates in the system, the more work that must be done at the pump, the more pressure that is seen at the sending unit. The flow is unchanged (at a given RPM). The pressures required to get that flow is changed. The energy that is wasted pumping is changed. The flow is not.
If you are given the task of moving a fluid through a pipe and the fluid flow must be constant, you will have to work harder to get a thick fluid through that pipe than if the fluid was less viscous. You would not have to turn the pump any faster. It would just be harder to turn.
Precisely. If the pump was producing constant pressure, then the pressure at given RPM would always be the same regardless of oil viscosity because the flow would change.
This is not a hard concept to grasp. Constant flow means the back pressure changes with viscosity, constant pressure means the flow changes with viscosity.
I'm going to try again. The oil pump DOES NOT provide constant pressure at a given RPM. Positive displacement pumps provide constant flow at a fixed RPM (with the caveats described earlier). The pressure is higher at the pump and at the sending unit due to the resistance of the fluid to flow. The thicker the fluid, the more force that accumulates in the system, the more work that must be done at the pump, the more pressure that is seen at the sending unit. The flow is unchanged (at a given RPM). The pressures required to get that flow is changed. The energy that is wasted pumping is changed. The flow is not.
If you are given the task of moving a fluid through a pipe and the fluid flow must be constant, you will have to work harder to get a thick fluid through that pipe than if the fluid was less viscous. You would not have to turn the pump any faster. It would just be harder to turn.
Precisely. If the pump was producing constant pressure, then the pressure at given RPM would always be the same regardless of oil viscosity because the flow would change.
This is not a hard concept to grasp. Constant flow means the back pressure changes with viscosity, constant pressure means the flow changes with viscosity.
Originally Posted By: MolaKule
A fluid's temperature rises because thermal energy is put into it by transfer from the hot engine parts to the fluid. Thermal energy is transferred via conduction, radiation, or convection.
I thought a lot of the heat that gets into the oil is created by the oils resistance to flow while pressure is being aspplied.
That is: consider oil flowing through a journal bearing. During the part of the cycle where pressures are very high, the oil is doing a lot of work trying to keep metal from touching metal, and in doing this work, the oil gets hotter.
Is this thought train impropper? or is there more heat absorbed by conduction with hot parts than is generated within the oil itself?
A fluid's temperature rises because thermal energy is put into it by transfer from the hot engine parts to the fluid. Thermal energy is transferred via conduction, radiation, or convection.
I thought a lot of the heat that gets into the oil is created by the oils resistance to flow while pressure is being aspplied.
That is: consider oil flowing through a journal bearing. During the part of the cycle where pressures are very high, the oil is doing a lot of work trying to keep metal from touching metal, and in doing this work, the oil gets hotter.
Is this thought train impropper? or is there more heat absorbed by conduction with hot parts than is generated within the oil itself?
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Originally Posted By: Brit33
That is very significant. What's the factory recommendation for this engine?
I ran my alfa at 120 km.hr for an hour and the temp. never rose about 90 degrees C. with TWS 10w60. Would be interesting to see it run on 10w40. But 90 is a good temp for oil to keep it clean.
Factory oil is Shell Ultra Helix (or Helix Ultra) 5W-40 HTHS 4.2cP.
I have run my F355 at 140 MPH for 10 minutes with the oil and water thermostats pegged at the thermostatic lower limits. Cars designed to run long and fast are designed with cooling capabilities that are completely foreign to more modest makes.
That is very significant. What's the factory recommendation for this engine?
I ran my alfa at 120 km.hr for an hour and the temp. never rose about 90 degrees C. with TWS 10w60. Would be interesting to see it run on 10w40. But 90 is a good temp for oil to keep it clean.
Factory oil is Shell Ultra Helix (or Helix Ultra) 5W-40 HTHS 4.2cP.
I have run my F355 at 140 MPH for 10 minutes with the oil and water thermostats pegged at the thermostatic lower limits. Cars designed to run long and fast are designed with cooling capabilities that are completely foreign to more modest makes.
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Imo (true or not),I feel thicker oil would keep parts cooler because it`s creating a thicker cushion/barrier between the moving parts.
Originally Posted By: GMorg
I'm going to try again. The oil pump DOES NOT provide constant pressure at a given RPM. Positive displacement pumps provide constant flow at a fixed RPM (with the caveats described earlier). The pressure is higher at the pump and at the sending unit due to the resistance of the fluid to flow. The thicker the fluid, the more force that accumulates in the system, the more work that must be done at the pump, the more pressure that is seen at the sending unit. The flow is unchanged (at a given RPM). The pressures required to get that flow is changed. The energy that is wasted pumping is changed. The flow is not.
If you are given the task of moving a fluid through a pipe and the fluid flow must be constant, you will have to work harder to get a thick fluid through that pipe than if the fluid was less viscous. You would not have to turn the pump any faster. It would just be harder to turn.
I don't disagree with your hypothetical description of the operation of a positive displacement oil pump but I think your not giving the "caveats" there due such as fluid slip which I suspect mounts as the back pressure rises in the system.
The bottom line is measured oil flow and it is universally accepted that an oil's viscosity affects the rate of oil flow through an engine.
In the cited test example, the difference in flow between the 20W-50 and 0W-20 was 14%, not a lot consdering the large difference in viscosity.
Assuming for the sake of argument that the 20W-50 had a HTHSV of 4.8cP and the 0W-20 2.6cP, that's a difference of 2.2cP which is a lot. The difference between a typical 2.6cP 20wt and a 3.1cP 30wt is only 0.5cP, so the reduction is flow will be under 3%; not a lot.
The big jump in reduced oil flow will occur in by-pass when the oil back pressure is capped. I suspect that is a big part of the reason for the 12% rise in oil temp's in Mitch Alsup's Ferrari in running the super heavy RL 15W-50 (HTHSV 5.8cP which is way heavier than even TWS 10W-60 with is HTHSV of 5.3cP before shearing and RL doesn't shear). Without doubt the Ferrari engine was in by-pass mode at high rev's with that oil.
I'm going to try again. The oil pump DOES NOT provide constant pressure at a given RPM. Positive displacement pumps provide constant flow at a fixed RPM (with the caveats described earlier). The pressure is higher at the pump and at the sending unit due to the resistance of the fluid to flow. The thicker the fluid, the more force that accumulates in the system, the more work that must be done at the pump, the more pressure that is seen at the sending unit. The flow is unchanged (at a given RPM). The pressures required to get that flow is changed. The energy that is wasted pumping is changed. The flow is not.
If you are given the task of moving a fluid through a pipe and the fluid flow must be constant, you will have to work harder to get a thick fluid through that pipe than if the fluid was less viscous. You would not have to turn the pump any faster. It would just be harder to turn.
I don't disagree with your hypothetical description of the operation of a positive displacement oil pump but I think your not giving the "caveats" there due such as fluid slip which I suspect mounts as the back pressure rises in the system.
The bottom line is measured oil flow and it is universally accepted that an oil's viscosity affects the rate of oil flow through an engine.
In the cited test example, the difference in flow between the 20W-50 and 0W-20 was 14%, not a lot consdering the large difference in viscosity.
Assuming for the sake of argument that the 20W-50 had a HTHSV of 4.8cP and the 0W-20 2.6cP, that's a difference of 2.2cP which is a lot. The difference between a typical 2.6cP 20wt and a 3.1cP 30wt is only 0.5cP, so the reduction is flow will be under 3%; not a lot.
The big jump in reduced oil flow will occur in by-pass when the oil back pressure is capped. I suspect that is a big part of the reason for the 12% rise in oil temp's in Mitch Alsup's Ferrari in running the super heavy RL 15W-50 (HTHSV 5.8cP which is way heavier than even TWS 10W-60 with is HTHSV of 5.3cP before shearing and RL doesn't shear). Without doubt the Ferrari engine was in by-pass mode at high rev's with that oil.
My 63 427 loves 20W50...
CATERHAM: OK, so we are on the same page except for the how much slippage occurs and whether it is universally related to viscosity. In the link that you provided, the 20W50 averages about 7% greater flow than the SAE30. In this case, two full SAE grade increases resulted in greater flow based on the data that you cite. If increased viscosity universally decreases flow, how can this be?
Likewise, the 0w10 and the 0w20 have the same flow rate (although it is noted that the 0w10 is an average of peak flow which implies that true average flow would be lower). Again, how can universally accepted positions apply to this example?
In the end, the ability of the oil to provide a seal at the clearance sites (gear to gear, gear to housing, and gear to thrust plates) will determine slippage. For Newtonian fluids, this phenomenon would be directly related to viscosity. However, modern oils are not Newtonian fluids and their behavior in the pump does not seem predictable by viscosity alone. I would suggest that reason that the SAE30 does not fall on the same curve as the other fluids is because it may be the only fluid that should behave as a Newtonian fluid. The 0w10 may also fall into that category.
I have tried to track down a paper from the late '70s that showed that the major predictor of flow rate was the VII that was used to formulate the oil as opposed to the actual viscosity. Since I cannot find the paper, I can't really use it as evidence.
I grant that slippage is real and it impacts pump output. I am still at a loss as to why a universal assumption that slippage is always predictable from viscosity would be valid.
Likewise, the 0w10 and the 0w20 have the same flow rate (although it is noted that the 0w10 is an average of peak flow which implies that true average flow would be lower). Again, how can universally accepted positions apply to this example?
In the end, the ability of the oil to provide a seal at the clearance sites (gear to gear, gear to housing, and gear to thrust plates) will determine slippage. For Newtonian fluids, this phenomenon would be directly related to viscosity. However, modern oils are not Newtonian fluids and their behavior in the pump does not seem predictable by viscosity alone. I would suggest that reason that the SAE30 does not fall on the same curve as the other fluids is because it may be the only fluid that should behave as a Newtonian fluid. The 0w10 may also fall into that category.
I have tried to track down a paper from the late '70s that showed that the major predictor of flow rate was the VII that was used to formulate the oil as opposed to the actual viscosity. Since I cannot find the paper, I can't really use it as evidence.
I grant that slippage is real and it impacts pump output. I am still at a loss as to why a universal assumption that slippage is always predictable from viscosity would be valid.
The oil temp's for the test of 162-166F are not very high so a low VI mineral straight 30wt being not much lighter than a synthetic 20W-50 doesn't surprise me.
Same goes for the 5W-20 and the 0W-10 and 0W-20 race oils. I'm sure if we new the actual HTHSV and VI spec's the closeness of the results would be clearer although there is a discrepancy in that the 0W-10 should have a higher flow rate if the OP is indeed lower. Could be a typo for all we know.
This a very small sample, but the gist of the matter is that the clearly heavier oils flowed less than the light 20wt oils.
I think the amount of slippage is directly related to the amount of back-pressure in the system. One could always contact one of the oil pump manufacturers mentioned in the article and see if they can shead more light on the subject.
Same goes for the 5W-20 and the 0W-10 and 0W-20 race oils. I'm sure if we new the actual HTHSV and VI spec's the closeness of the results would be clearer although there is a discrepancy in that the 0W-10 should have a higher flow rate if the OP is indeed lower. Could be a typo for all we know.
This a very small sample, but the gist of the matter is that the clearly heavier oils flowed less than the light 20wt oils.
I think the amount of slippage is directly related to the amount of back-pressure in the system. One could always contact one of the oil pump manufacturers mentioned in the article and see if they can shead more light on the subject.
Well, I took CATERHAM's advice. According to every pump manufacturer (and a few educational sites) that I can find that offers web-accessible info, as oil viscosity increases, slippage decreases, the pump efficiency increases and pump output increases (when on test rigs). In practice, when mounted, the pick-up screen and pick-up tube diameter can become limiting as viscosity increases and a vacuum is created. As a result, the vapor pressure of the oil and the differential in pressure between the pump and the sump determines if cavitation occurs. If cavitation begins to occur, pump output can decrease due to cavitation. So, in practice, output decreases as viscosity increases when the oil's vapor pressure allows cavitation.
Other sources of flow loss due to increased viscosity are mated surfaces on the pump. Since most pumps do not use gaskets and mounting surfaces aren't perfect, the pumps simply leak. As a result, as pressure builds, oil can leak from mated sufaces.
All pump literature that I could find attributed increases in oil temps with increase viscosity to be due to the increased energy that it takes to pump the fluid. Some also noted that when flow rate decreases, primarily due to high bearing velocity, the oil has higher resident time in bearings and can come closer to equilibrium with the metal surfaces. The oil exits the bearing hotter, but due to lower flow, actually removes less heat.
I need to apologize for stealing the thread. Thanks for tolerating the distraction. I learned something.
Other sources of flow loss due to increased viscosity are mated surfaces on the pump. Since most pumps do not use gaskets and mounting surfaces aren't perfect, the pumps simply leak. As a result, as pressure builds, oil can leak from mated sufaces.
All pump literature that I could find attributed increases in oil temps with increase viscosity to be due to the increased energy that it takes to pump the fluid. Some also noted that when flow rate decreases, primarily due to high bearing velocity, the oil has higher resident time in bearings and can come closer to equilibrium with the metal surfaces. The oil exits the bearing hotter, but due to lower flow, actually removes less heat.
I need to apologize for stealing the thread. Thanks for tolerating the distraction. I learned something.
Originally Posted By: FZ1
So,then,in the end,thinner runs cooler,right? Lol.
In my case I wouldn't want oil to be cooler than 80c.
Normal road trip on the highway for 45 minutes at a moderate speed with Castrol TWS 10w60 and it didn't exceed 80c.
If I push the car faster it will max at 90c.
I know TWS has a lowish HTHS compared to better Motul oils.
Maybe I'd get the same temp. with 300v 15w/50.
Thinking about trying Mobil 1 5w50 next year. I have a friend who works for the company.
It has a HTHS of 4.4, not sure what pressure drop I'd see.
But nice cold start ups with a 5W I imagine.
So,then,in the end,thinner runs cooler,right? Lol.
In my case I wouldn't want oil to be cooler than 80c.
Normal road trip on the highway for 45 minutes at a moderate speed with Castrol TWS 10w60 and it didn't exceed 80c.
If I push the car faster it will max at 90c.
I know TWS has a lowish HTHS compared to better Motul oils.
Maybe I'd get the same temp. with 300v 15w/50.
Thinking about trying Mobil 1 5w50 next year. I have a friend who works for the company.
It has a HTHS of 4.4, not sure what pressure drop I'd see.
But nice cold start ups with a 5W I imagine.
GMorg thanks for doing the research.
Some of the explanations such as leakage are as I would expect while others are not.
Some of the explanations such as leakage are as I would expect while others are not.
In an idealized situation, there would not be a difference in flow. In the real world, there apparently can be. That was the earlier dispute. If you throw in times when the bypass is engaged, the differences can be much larger.
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