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      04-01-2014, 06:27 PM   #1
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Using 0W40 = more oil flow is false

To start off I would like to introduce myself. I am a chemical engineer. I have a good understanding of hydraulic (how fluid flow) and pumps.

I want bring up the point using 0w40 to minimize bearing wear. The idea is that thinner oil will have more of flow compared to thicker oil. Therefore, it will provide better protection for daily driving.

Because I am not an automotive engineer, I have no idea what protects an engine better. However as a chemical engineer, I can say the statement of using thinner oil will result more flow in a car engine is incorrect. The reason is because the oil pumps in cars are positive displacement pumps. The basic idea of a positive displacement pumps is it will always move the designed amount of volume regardless of discharge pressure. The reality is pump discharge pressure does have a small effect on flow rate due to pump imperfections. But for this discussion, I will limit it to only theoretically how positive displacement pumps operate and not reality.

Based on positive displacement pump principle, the amount of engine oil that goes through oil pump is the same regardless of oil viscosity (0w-40 vs 10w-10) as long as the pump has enough power. Before anyone say “does that mean I can use 10w-100 because viscosity doesn’t matter in positive displacement pump,” the answer to that question is both yes and no. If the pump has enough power and the pump components are strong enough, the theoretical flow rate of 10w-100 and 0w-40 is the same through a positive displacement pump. However, the oil pump in cars are limited by timing belt (I think that’s the components that connect the oil pump to the engine) and pump components as they are not strong enough to handle all of an engine’s power. That is why relieve valves are installed to prevent overloading the pump. So if you use too thick of oil, the pump discharge pressure would be high causing the relieve valve to open. When the relieve valve opens, some flow is diverted back to the oil pan without going to the engine components. To summarize, if too thick of oil is used and the oil pump has enough power, the flow rate through the positive displacement pump would be the same. However, the oil going to your engine components will reduce dramatically as most flow is diverted directly back to the oil pan through the relieve valve.

If S65 oil system is designed for 10w60, I don’t see how using thinner oil will result in more flow.

Positive displacement pump:
Thick oil = higher discharge pressure = flow unchanged
Thinner oil = lower discharge pressure = flow unchanged
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      04-01-2014, 06:46 PM   #2
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I don't think the argument is more flow... the argument is that 0w40 has better lubrication of the bearings as the thinner oil can get into smaller places than the thicker oil.
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      04-01-2014, 07:10 PM   #3
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      04-01-2014, 07:16 PM   #4
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I would like to talk about is conservation of mass. Matter cannot be create or destroyed blah blah blah. So if 5 gallons of oil goes in 5 gallons of oil must come out. If more oil is coming out of the smaller bearing clearance, that means less oil in coming out of other place in order to satisfy the conservation of mass law. Fluid takes the path of least resistance. Meaning under the same pressure, you can get more flow through a larger diameter pipe compared to a smaller diameter pipe. In order for more fluid to come out of the bearings, other oil path must reduce flow rate. Therefore, in order for more oil to come out of the bearing the restriction of other path must increased. That's like saying because I used thinner oil, other oil path pipe diameter became smaller.

Like I said I am not an automotive engineer and would love to have input on anything I miss.
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      04-01-2014, 07:22 PM   #5
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Quote:
Originally Posted by Smiley913 View Post
To start off I would like to introduce myself. I am a chemical engineer. I have a good understanding of hydraulic (how fluid flow) and pumps.

I want bring up the point using 0w40 to minimize bearing wear. The idea is that thinner oil will have more of flow compared to thicker oil. Therefore, it will provide better protection for daily driving.

Because I am not an automotive engineer, I have no idea what protects an engine better. However as a chemical engineer, I can say the statement of using thinner oil will result more flow in a car engine is incorrect. The reason is because the oil pumps in cars are positive displacement pumps. The basic idea of a positive displacement pumps is it will always move the designed amount of volume regardless of discharge pressure. The reality is pump discharge pressure does have a small effect on flow rate due to pump imperfections. But for this discussion, I will limit it to only theoretically how positive displacement pumps operate and not reality.

Based on positive displacement pump principle, the amount of engine oil that goes through oil pump is the same regardless of oil viscosity (0w-40 vs 10w-10) as long as the pump has enough power. Before anyone say “does that mean I can use 10w-100 because viscosity doesn’t matter in positive displacement pump,” the answer to that question is both yes and no. If the pump has enough power and the pump components are strong enough, the theoretical flow rate of 10w-100 and 0w-40 is the same through a positive displacement pump. However, the oil pump in cars are limited by timing belt (I think that’s the components that connect the oil pump to the engine) and pump components as they are not strong enough to handle all of an engine’s power. That is why relieve valves are installed to prevent overloading the pump. So if you use too thick of oil, the pump discharge pressure would be high causing the relieve valve to open. When the relieve valve opens, some flow is diverted back to the oil pan without going to the engine components. To summarize, if too thick of oil is used and the oil pump has enough power, the flow rate through the positive displacement pump would be the same. However, the oil going to your engine components will reduce dramatically as most flow is diverted directly back to the oil pan through the relieve valve.

If S65 oil system is designed for 10w60, I don’t see how using thinner oil will result in more flow.

Positive displacement pump:
Thick oil = higher discharge pressure = flow unchanged
Thinner oil = lower discharge pressure = flow unchanged
Sorry my friend, but you are forgetting that the positive displacement oil pumps in engines have a relief valve in the system that sends oil that is over the relief valve pressure setting back to the sump before it reaches the main oil gallery of the engine. So even though the positive displacement pump is moving the same amount of oil with every revolution the oil that goes back to the sump is not reaching the engine for lubrication purposes.

Secondly the oil pump in the S65 is a variable displacement pressure compensated pump....... When pressure is low the pump displacement is increased until the preset compensator pressure is reached....... The thinner the oil, the more flow it will take to reach the pressure compensator setting.

Sorry my friend, your fundamentals are right but you missed some details. If engines had simple positive displacement pumps with no relief circuit, lines and filters would be blown and that is not acceptable.

Remember ,the relief valve in the lubrication system of an engine sends flow back to the sump when the pressure is above the relief valve setting (for example during a cold start or when a higher viscosity oil is used)....... This is effectively limiting oil flow to the engine bearings, etc. because the relief valve dumps back to the sump as right after the pump.

To sum up:

1)The oil pump in the S65 will indeed flow more oil with a thinner oil than a thicker oil due to it's variable displacement/pressure compensated design.

2)A conventional fixed displacement pump in most normal engines will flow the same amount of oil regardless of viscosity, but the higher pressure that is a result of the higher viscosity oil will mean more oil is going over relief and back to the sump without reaching the engine...... This will also effectively limit oil flow to the engine compared to a lower viscosity oil.
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      04-01-2014, 07:22 PM   #6
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Quote:
Originally Posted by Smiley913 View Post
I would like to talk about is conservation of mass. Matter cannot be create or destroyed blah blah blah. So if 5 gallons of oil goes in 5 gallons of oil must come out. If more oil is coming out of the smaller bearing clearance, that means less oil in coming out of other place in order to satisfy the conservation of mass law. Fluid takes the path of least resistance. Meaning under the same pressure, you can get more flow through a larger diameter pipe compared to a smaller diameter pipe. In order for more fluid to come out of the bearings, other oil path must reduce flow rate. Therefore, in order for more oil to come out of the bearing the restriction of other path must increased. That's like saying because I used thinner oil, other oil path pipe diameter became smaller.

Like I said I am not an automotive engineer and would love to have input on anything I miss.
The one thing I'll add is that 0W40 warms up faster than 10W60. It's argued that most of the bearing wear is when the oil is cold, so the faster the warm up, the better.

And on that note, I'm turning into a spectator from here on out.
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      04-01-2014, 07:39 PM   #7
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Originally Posted by BMRLVR View Post
Sorry my friend, but you are forgetting that the positive displacement oil pumps in engines have a relief valve in the system that sends oil that is over the relief valve pressure setting back to the sump before it reaches the main oil gallery of the engine. So even though the positive displacement pump is moving the same amount of oil with every revolution the oil that goes back to the sump is not reaching the engine for lubrication purposes.

Secondly the oil pump in the S65 is a variable displacement pressure compensated pump....... When pressure is low the pump displacement is increased until the preset compensator pressure is reached....... The thinner the oil, the more flow it will take to reach the pressure compensator setting.

Sorry my friend, your fundamentals are right but you missed some details. If engines had simple positive displacement pumps with no relief circuit, lines and filters would be blown and that is not acceptable.

Remember ,the relief valve in the lubrication system of an engine sends flow back to the sump when the pressure is above the relief valve setting (for example during a cold start or when a higher viscosity oil is used)....... This is effectively limiting oil flow to the engine bearings, etc. because the relief valve dumps back to the sump as right after the pump.
So you are saying the engineers at BWM designed the oil system such that when using 10W60 the relieve valve is always open diverting some flow back to the pan, but when I use 0w40 under similar condition the relieve valve is closed.

Sure can you tell me what is the relieve valve pressure set at? If it is set at 90 psi (arbitrary #), using 10w60 and 0w40 for daily driving would never pop the relieve valve. So the flow rate for both oil through a positive displacement pump is the same. If it is set at 50 psi, high rpm would destroy the engine as the oil pressure builds too high and most oil is diverted from the engine components. If I were designing, I would set the relieve valve pressure high.

Let me look up this variable displacement pressure compensated pump
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      04-01-2014, 08:09 PM   #8
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      04-01-2014, 08:15 PM   #9
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Quote:
Originally Posted by Smiley913 View Post
To start off I would like to introduce myself. I am a chemical engineer. I have a good understanding of hydraulic (how fluid flow) and pumps.

I want bring up the point using 0w40 to minimize bearing wear. The idea is that thinner oil will have more of flow compared to thicker oil. Therefore, it will provide better protection for daily driving.

Because I am not an automotive engineer, I have no idea what protects an engine better. However as a chemical engineer, I can say the statement of using thinner oil will result more flow in a car engine is incorrect. The reason is because the oil pumps in cars are positive displacement pumps. The basic idea of a positive displacement pumps is it will always move the designed amount of volume regardless of discharge pressure. The reality is pump discharge pressure does have a small effect on flow rate due to pump imperfections. But for this discussion, I will limit it to only theoretically how positive displacement pumps operate and not reality.

Based on positive displacement pump principle, the amount of engine oil that goes through oil pump is the same regardless of oil viscosity (0w-40 vs 10w-10) as long as the pump has enough power. Before anyone say “does that mean I can use 10w-100 because viscosity doesn’t matter in positive displacement pump,” the answer to that question is both yes and no. If the pump has enough power and the pump components are strong enough, the theoretical flow rate of 10w-100 and 0w-40 is the same through a positive displacement pump. However, the oil pump in cars are limited by timing belt (I think that’s the components that connect the oil pump to the engine) and pump components as they are not strong enough to handle all of an engine’s power. That is why relieve valves are installed to prevent overloading the pump. So if you use too thick of oil, the pump discharge pressure would be high causing the relieve valve to open. When the relieve valve opens, some flow is diverted back to the oil pan without going to the engine components. To summarize, if too thick of oil is used and the oil pump has enough power, the flow rate through the positive displacement pump would be the same. However, the oil going to your engine components will reduce dramatically as most flow is diverted directly back to the oil pan through the relieve valve.

If S65 oil system is designed for 10w60, I don’t see how using thinner oil will result in more flow.

Positive displacement pump:
Thick oil = higher discharge pressure = flow unchanged
Thinner oil = lower discharge pressure = flow unchanged
Sorry but you have no clue what you are talking about. I don't even know where to begin so I will just skip this one.
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      04-01-2014, 08:26 PM   #10
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      04-01-2014, 08:59 PM   #11
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Originally Posted by kawasaki00 View Post
Sorry but you have no clue what you are talking about. I don't even know where to begin so I will just skip this one.
Like I said, I am not an automotive engineer and I might be wrong on the oil system in this car. I would love to learn more facts. Any one can tell another person they are wrong. Some facts to back up your claim would be nice.
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      04-01-2014, 09:06 PM   #12
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Some facts on positive displacement pump:
http://www.pumpschool.com/intro/pd%20vs%20centrif.pdf

If the oil system is not using a positive displacement pump, I am complete wrong.
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      04-01-2014, 09:19 PM   #13
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I'm not an oil guy...and don't pretend to know anything about it.
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      04-01-2014, 09:22 PM   #14
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Quote:
Originally Posted by Smiley913
Some facts on positive displacement pump:
http://<a href="http://www.pumpschoo...entrif.pdf</a>

If the oil system is not using a positive displacement pump, I am complete wrong.
You are correct on how the pumps work. The issue is that you are implying that the system is going to have no way to control flow. The flow from the pump needs to be controlled or relieved back to the sump because the S65 has an operating range between ~600RPM and 8400RPM. Imagine if there was no relief valve or pressure compensation on the main pump. Imagine the additional flow that occurs at 8400RPM compared to idle. The pump would literally destroy itself if there was no way for flow to make its way back to the sump.

Your documentation is with regards to pumps used in industrial plant settings. These pumps run at relatively constant speeds and the systems are usually protected by rupture disks and not relief valves.

I appreciate you trying to contribute, but, the application is different and your examples don't apply to a lubrication in an engine.
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      04-01-2014, 09:27 PM   #15
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I think a "thanks but no thanks" is in order
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      04-01-2014, 10:01 PM   #16
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Quote:
Originally Posted by BMRLVR View Post
You are correct on how the pumps work. The issue is that you are implying that the system is going to have no way to control flow. The flow from the pump needs to be controlled or relieved back to the sump because the S65 has an operating range between ~600RPM and 8400RPM. Imagine if there was no relief valve or pressure compensation on the main pump. Imagine the additional flow that occurs at 8400RPM compared to idle. The pump would literally destroy itself if there was no way for flow to make its way back to the sump.

Your documentation is with regards to pumps used in industrial plant settings. These pumps run at relatively constant speeds and the systems are usually protected by rupture disks and not relief valves.

I appreciate you trying to contribute, but, the application is different and your examples don't apply to a lubrication in an engine.

I will contribute a little tomorrow. I have had a less than desirable night due to other people's driving skills.
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      04-01-2014, 10:06 PM   #17
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Sorry but you have no clue what you are talking about. I don't even know where to begin so I will just skip this one.
OK, now that I read it...I have to agree. And since this has nothing to do with oil, I feel more comfortable commenting.

Smiley, you presented your credentials and premise of this article based on being a chemical engineer, but your premise and entire discussion concerns mechanical engineering and fluid dynamics (if that's the right terminology here).

This is a case where you really need to see how the engine works before starting a thread like this. A timing belt drives the cams and usually only exists on small 4-banger engines. A timing CHAIN drives the cams, but is much stronger than a timing belt. A timing belt is hung outside the block, and timing chain is hung inside it.

I've seen oil pumps driven directly from intermediate shafts, shafts driven from other gears, and chains driven directly from the nose of the crank. But I've never seen one driven from a timing belt or timing chain (I'm not saying they don't exist). When you say this is necessary because the oil pump can't handle all of the engine's power, I've got to be honest that I don't even know what that means. If you're saying the oil pump needs a gear reduction to operate at the proper speed, well maybe it does. That's normal.

I've been involved in many of these bearing discussions and I don't recall any of them turning into the premise you posed in this article. I'm not saying that it hasn't come up, but I don't remember any such discussion before. I do remember one side saying 10W60 is too thick and advocating 0W40. The other said says 0W40 is too thin and will reduce oil pressure across the bearings. That's when the pro 0W40 side counters by bringing up a positive displacement pump and saying that it's not possible. But I've never seen anybody talk about flow rates with different viscosities being the reason not to switch oils. Translation: the premise of this thread isn't what the discussion has even been about.
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      04-01-2014, 10:08 PM   #18
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Quote:
Originally Posted by Smiley913 View Post
Some facts on positive displacement pump:
http://www.pumpschool.com/intro/pd%20vs%20centrif.pdf

If the oil system is not using a positive displacement pump, I am complete wrong.
The problem here is this: the entire premise of your thread is wrong. I don't think the argument has ever been about oil flow through the pump.
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      04-01-2014, 11:15 PM   #19
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OK, now that I read it...I have to agree. And since this has nothing to do with oil, I feel more comfortable commenting.

Smiley, you presented your credentials and premise of this article based on being a chemical engineer, but your premise and entire discussion concerns mechanical engineering and fluid dynamics (if that's the right terminology here).

This is a case where you really need to see how the engine works before starting a thread like this. A timing belt drives the cams and usually only exists on small 4-banger engines. A timing CHAIN drives the cams, but is much stronger than a timing belt. A timing belt is hung outside the block, and timing chain is hung inside it.

I've seen oil pumps driven directly from intermediate shafts, shafts driven from other gears, and chains driven directly from the nose of the crank. But I've never seen one driven from a timing belt or timing chain (I'm not saying they don't exist). When you say this is necessary because the oil pump can't handle all of the engine's power, I've got to be honest that I don't even know what that means. If you're saying the oil pump needs a gear reduction to operate at the proper speed, well maybe it does. That's normal.

I've been involved in many of these bearing discussions and I don't recall any of them turning into the premise you posed in this article. I'm not saying that it hasn't come up, but I don't remember any such discussion before. I do remember one side saying 10W60 is too thick and advocating 0W40. The other said says 0W40 is too thin and will reduce oil pressure across the bearings. That's when the pro 0W40 side counters by bringing up a positive displacement pump and saying that it's not possible. But I've never seen anybody talk about flow rates with different viscosities being the reason not to switch oils. Translation: the premise of this thread isn't what the discussion has even been about.
I don't know but what means the oil pump is connected to the engine that is why I put the indication it was a guess. When I say the oil pump can't handle all of engine's power, I was just trying to say the pump would break if it is connected to a 400 hp motor. The oil pump is probably only using a small amount of the total engine power (guess: less than 1 hp).

Quote:
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The problem here is this: the entire premise of your thread is wrong. I don't think the argument has ever been about oil flow through the pump.
Got it. I thought when people say more oil it means overall (through the pump).

I am not trying to prove anything. All I want to do is have a logical discussion and understand the things I don't understand.
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      04-01-2014, 11:23 PM   #20
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You are correct on how the pumps work. The issue is that you are implying that the system is going to have no way to control flow. The flow from the pump needs to be controlled or relieved back to the sump because the S65 has an operating range between ~600RPM and 8400RPM. Imagine if there was no relief valve or pressure compensation on the main pump. Imagine the additional flow that occurs at 8400RPM compared to idle. The pump would literally destroy itself if there was no way for flow to make its way back to the sump.

Your documentation is with regards to pumps used in industrial plant settings. These pumps run at relatively constant speeds and the systems are usually protected by rupture disks and not relief valves.

I appreciate you trying to contribute, but, the application is different and your examples don't apply to a lubrication in an engine.
I understand your logic but still have some question. I will ask them tomorrow.

But some information regarding the industry. Most industry uses relief valves as to rupture disk. The reason is if a rupture disk opens due to pressure you have to replace it. That means shutting down the process. It can take minutes to days to get the replacement part and process going again. In oil and gas, some platform can make up 200 million a day the price of relieve valve compared to that is nothing.
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      04-01-2014, 11:33 PM   #21
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I don't know but what means the oil pump is connected to the engine that is why I put the indication it was a guess. When I say the oil pump can't handle all of engine's power, I was just trying to say the pump would break if it is connected to a 400 hp motor. The oil pump is probably only using a small amount of the total engine power (guess: less than 1 hp).
But the pump is connected to the engine, by way of a gear on the nose of the crankshaft. See photos below.

Quote:
Got it. I thought when people say more oil it means overall (through the pump).

I am not trying to prove anything. All I want to do is have a logical discussion and understand the things I don't understand.
Got it. No worries.

Here's pictures of the S65 oil pump assembly. Notice there are actually two pumps. One pump simply drags oil from the rear to the front of the sump (or I may have it backwards...it's late). The main oil pump is driven directly from the front gear on the crankshaft (see photo-1). In Photo-2, you can see the oil pump with gear that drives directly from the crankshaft. The secondary pump is driven from the chain you see. The secondary pump pull oil from the rear of the sump to the front.

I hope this helps visualize the engine a little better.







Full set of engine disassembly pictures:
http://www.rcollins-home.org/photobu....php?album=204
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      04-01-2014, 11:54 PM   #22
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OK, now that I read it...I have to agree. And since this has nothing to do with oil, I feel more comfortable commenting.

Smiley, you presented your credentials and premise of this article based on being a chemical engineer, but your premise and entire discussion concerns mechanical engineering and fluid dynamics (if that's the right terminology here).

This is a case where you really need to see how the engine works before starting a thread like this. A timing belt drives the cams and usually only exists on small 4-banger engines. A timing CHAIN drives the cams, but is much stronger than a timing belt. A timing belt is hung outside the block, and timing chain is hung inside it.

I've seen oil pumps driven directly from intermediate shafts, shafts driven from other gears, and chains driven directly from the nose of the crank. But I've never seen one driven from a timing belt or timing chain (I'm not saying they don't exist). When you say this is necessary because the oil pump can't handle all of the engine's power, I've got to be honest that I don't even know what that means. If you're saying the oil pump needs a gear reduction to operate at the proper speed, well maybe it does. That's normal.

I've been involved in many of these bearing discussions and I don't recall any of them turning into the premise you posed in this article. I'm not saying that it hasn't come up, but I don't remember any such discussion before. I do remember one side saying 10W60 is too thick and advocating 0W40. The other said says 0W40 is too thin and will reduce oil pressure across the bearings. That's when the pro 0W40 side counters by bringing up a positive displacement pump and saying that it's not possible. But I've never seen anybody talk about flow rates with different viscosities being the reason not to switch oils. Translation: the premise of this thread isn't what the discussion has even been about.
I don't know but what means the oil pump is connected to the engine that is why I put the indication it was a guess. When I say the oil pump can't handle all of engine's power, I was just trying to say the pump would break if it is connected to a 400 hp motor. The oil pump is probably only using a small amount of the total engine power (guess: less than 1 hp).

Quote:
Originally Posted by regular guy View Post
The problem here is this: the entire premise of your thread is wrong. I don't think the argument has ever been about oil flow through the pump.
Got it. I thought when people say more oil it means overall (through the pump).

I am not trying to prove anything. All I want to do is have a logical discussion and understand the things I don't understand.
The oil pump is indeed driven directly off of the crank and if it wasn't feeding a system with a pressure compensator or relief valve it would take as much of the engines' power as it needed to turn it. Since the pump in the S65 is pressure compensated and has a relief valve that sets the ultimate amount of power it takes to turn the pump. For example It takes X amount of horsepower to make Y amount of pressure. As Y is increased X has to increase proportionately.
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