Fluid dyamics discussion - someone educate me.....

[440Magnum]

Originally Posted By: IndyIan
In theory, shouldn't the oil passages should be sized large enough that they should act like a pressure "tank" so all the bearings receive equal pressure?



Well, the oil is incompressible so the galleries can't really act like a "tank." Ideally their cross-section *should* be large enough that they don't cause a significant pressure drop... but have you ever looked at an as-built engine casting? They're always rough and frequently have a number of restrictions where various parts of the casting mold meet. Many pushrod v8s also have the lifters partially intruding into the two main upper galleries, which reduces cross section somewhat. That's one thing that you can do *way* better than the factory when you rebuild an engine- just run a long drill bit down every oil gallery to knock off the roughness of surfaces and open up any obstructions. Oiling system reliability goes way up with nothing more than that. Its less of a problem with newer aluminum casting methods than it was with sand-core cast iron blocks, but it still isn't a perfect production process. Even in a perfectly prepped oil system, odd things can happen at high RPM though. Since the oil feeds into the main bearings and flows through passages inside the crankshaft to get to the rod bearings, the crank becomes a big centrifuge at high RPM and flings all the oil out to the rod bearings so that if any one main is a little low on flow, the crank can actually suck air *in* at the main and cause it to intermittently go dry. By the same token, when the crank becomes a centrifugal pump like that it starts "sucking" oil down the galleries causing faster oil flow and the pressure drop can get bigger. Not usually a problem in street engines, but it can happen.

 

[440Magnum]

Originally Posted By: Brian_Bowers

My main concern in all of this is trying to figure out why my oil pressure went from 50ish to 40ish at hot idle... I don't see how hitting the chunk of concrete could have changed anything. If it did, I'd think it would manifest itself all the time i.e hot cruise and WOT, but the only difference I'm seeing is at hot idle.



A few things to consider:

First off, are you using a factory electric pressure gauge to make these judgments? They're notoriously inaccurate and also prone to change over time- both in offset and in linearity.

Second- at hot idle, the pressure relief valve is going to be closed and any oil pressure you build will be due to the fixed displacement of the oil pump working against the combined "leaks" (clearances) in the oiling system. If the oil leaks a little faster now than it used to or if the pump moves a tick less per turn now than it used to (both happen due to normal wear), or if the oil is slightly thinner now than before, then the pressure at hot idle will be lower. Once you go to higher RPM, the pressure gets set by the relief valve. The pump has a surplus of oil to deliver and the relief valve opens only enough to dump any oil over the amount required to hit its setpoint- so the hot/high RPM number won't change very much with normal engine wear over time (unless the wear is so great that the relief valve never opens), nor will it change (within reasonable limits...) with slightly thinner or thicker oil.

 

[Gary Allan]

Originally Posted By: Brian_Bowers
So if the volume at idle is a fixed rate wouldn't changing the flow path characteristics via a more restrictive filter or an oil cooler cause the resultant pressure to change?

What about the questions in my above post... I appreaciat the help... trying to understand what's going on.


Sure, as it is read at the pump. As read at the end, assuming reasonable efficiency of the pump and not being in relief, it should be the same.

If you're reading less at the point cited in the diagram ..and you're below relief at the pump, then you're not at the same visc. You're allegedly only dropping 2PSID across all those elements. Not likely.

The thing is, with you alleged relief limit at the pump, you have to be in relief to ever read 40psi at that point in the system. You will be at elevated PSID across everything. Filter, cooler ..every part of the engine. The only thing making oil choose the engine over the relief is the size of the relief port and what the engine will flow @ 42psi at the pump.

This is indifferent to subsets where the flow branches off. It still looks like one flow as far as the pump is concerned.

 

[jmb106]

Originally Posted By: Brian_Bowers
Here's what's going on with my car... a 2001 Z06 Corvette with 84,000 miles on it.

In early 2007 I installed a new cam, high volume LS4 oil pump, and a Dewitts radiator with left side EOC (enclosed oil cooler). Running Amsoil 5w40 and a K&N filter I would see 47-49 psi at hot idle (210ish oil temp) and around 60 hot cruise and 78-80 at WOT. On track where oil temps maxed out at 250ish I was never below 50psi at WOT which was perfect.

Now that the car is no longer tracked (have a dedicated track car) I removed the oil cooler and radiator earlier this year. I was seeing low 50s at hot idle and mid 60s hot cruise and 84 max at WOT. This was in February and I never really paid attention to it after that.

Last week I hit a chunk of concrete on the highway and as I pulled off I watched the oil pressure closely to make sure I didn't tear the filter or crack the pan. As I cam to an idle I saw the pressure drop to 44... then at the next light it dropped to 35psi. Thinking I'd damaged something I pulled over and found no damage... even jacking it up the only damage was a scraped cross-member and a small scratch on my oil pan.

So... after that I was seeing 40psi at hot idle, 60 at cruise, and low 80s at WOT. I chalked it up to it being the summer heat etc. but oil temps are the same when hot.

Last weekend I put in fresh M1 5w30 and a M1 filter becuase the Amsoil in the car was 11 months old. Now I'm seeing 35-36psi at hot idle, 57-60 hot cruise, and low 80s WOT.

My main concern in all of this is trying to figure out why my oil pressure went from 50ish to 40ish at hot idle... I don't see how hitting the chunk of concrete could have changed anything. If it did, I'd think it would manifest itself all the time i.e hot cruise and WOT, but the only difference I'm seeing is at hot idle.

I'm trying to determine if removing the oil cooler actually caused my oil pressure at idle to go down, but when I first checked it back in Feb/Marh I may have not been looking at it at full hot.

I know it's a bit long, but I'm trying to understand the effects of removing my oil cooler and then subsequently moving to a more restrictive oil filter.

The real thing to do would be to put Amsoil 5w40 back in it w/ a K&N filter and see what happens, but I don't care to spend $14 on the fitler and $10 a quart on oil anymore when I'm not trackign the car.


You went from a thicker 40w oil at operating temps to a thinner 30w oil at operating temp, the 30w oil is flowing more, there for lower oil pressure! the 30w oil at 100*c has less restriction to flow than the 40w oil you had in there before!

 

[BuickGN]

Originally Posted By: jmb106
Originally Posted By: Brian_Bowers
Here's what's going on with my car... a 2001 Z06 Corvette with 84,000 miles on it.

In early 2007 I installed a new cam, high volume LS4 oil pump, and a Dewitts radiator with left side EOC (enclosed oil cooler). Running Amsoil 5w40 and a K&N filter I would see 47-49 psi at hot idle (210ish oil temp) and around 60 hot cruise and 78-80 at WOT. On track where oil temps maxed out at 250ish I was never below 50psi at WOT which was perfect.

Now that the car is no longer tracked (have a dedicated track car) I removed the oil cooler and radiator earlier this year. I was seeing low 50s at hot idle and mid 60s hot cruise and 84 max at WOT. This was in February and I never really paid attention to it after that.

Last week I hit a chunk of concrete on the highway and as I pulled off I watched the oil pressure closely to make sure I didn't tear the filter or crack the pan. As I cam to an idle I saw the pressure drop to 44... then at the next light it dropped to 35psi. Thinking I'd damaged something I pulled over and found no damage... even jacking it up the only damage was a scraped cross-member and a small scratch on my oil pan.

So... after that I was seeing 40psi at hot idle, 60 at cruise, and low 80s at WOT. I chalked it up to it being the summer heat etc. but oil temps are the same when hot.

Last weekend I put in fresh M1 5w30 and a M1 filter becuase the Amsoil in the car was 11 months old. Now I'm seeing 35-36psi at hot idle, 57-60 hot cruise, and low 80s WOT.

My main concern in all of this is trying to figure out why my oil pressure went from 50ish to 40ish at hot idle... I don't see how hitting the chunk of concrete could have changed anything. If it did, I'd think it would manifest itself all the time i.e hot cruise and WOT, but the only difference I'm seeing is at hot idle.

I'm trying to determine if removing the oil cooler actually caused my oil pressure at idle to go down, but when I first checked it back in Feb/Marh I may have not been looking at it at full hot.

I know it's a bit long, but I'm trying to understand the effects of removing my oil cooler and then subsequently moving to a more restrictive oil filter.

The real thing to do would be to put Amsoil 5w40 back in it w/ a K&N filter and see what happens, but I don't care to spend $14 on the fitler and $10 a quart on oil anymore when I'm not trackign the car.


You went from a thicker 40w oil at operating temps to a thinner 30w oil at operating temp, the 30w oil is flowing more, there for lower oil pressure! the 30w oil at 100*c has less restriction to flow than the 40w oil you had in there before!


Whoa! I guess I missed that small fact which would explain a lot.

 

[Brian_Bowers]

Just to claify I noticed the pressure drop before I switched oils.... I swapped the oil to 5w30 last weekend. The wednesday before was when I hit the chunk of concrete and started watching oil pressure closely again.

I'm mostly trying to understand if removing my aftermarket oil cooler setup would cause a pressure drop at idle. Or... if somehow jarring the car I did something to reduce idle oil pressure.

 

[Gary Allan]

Me too

MY same rhetoric applies though.

 

[Brian_Bowers]

To make this easy...

5w40 oil + K&N filter + oil cooler setup = 47-49 psi hot idle

5w40 oil + K&N - oil cooler (February)= 50-53 psi hot idle

11 month old 5w40 oil + K&N - oil cooler (2 weeks ago) = 40 psi hot idle

5w30 oil + M1 = 36 psi hot idle

Basically... after I took out my oil cooler I was seeing 50s at hot idle... then after I hit a chunk of concrete on the highway I noticed I was at 40 which I'd never seen before.

I put in fresh oil to see if it was 11-month old oil contributing to the drop in pressure, but didn't want to buy Amsoil so I went w/ M1 5w30 seeing as the car won't see track use anymore.

I'm trying to troubleshoot the reduction in oil pressure and see if I could have jarred anything.

OR

If the removal of the oil cooler lowered my oil pressure, but when I initially paid attention to it back in February I may have been looking at semi-warmed pressures.

In my head I expected the removal of the cooler to bump pressures so once I took note of it I stopped paying close attention until I hit the concrete the week before last.

 

[Gary Allan]

The cooler could have been a neutral installation. It cooled the oil keeping it at a higher visc at temp ..but added "back pressure" of its own. It always "depends".

 

[SuperBusa]

Originally Posted By: Gary Allan
It's pretty simple. Below the relief level (that is seen at the pump) ..there is no such thing as a restriction. Assuming that the pump is of reasonable efficiency, the fluid will merely accelerate and will evidence a "pressure elevation" upstream of the choke.


See red text above. Technically, even when the pump is not in relief mode there is still "restriction". That flow restriction is what causes the pump to produce pressure at the volume it's putting out. If there was no restriction downstream of the pump, then the pump's output pressure would be near zero. The higher the restriction, the higher the pressure is required to force X gpms down the flow path. Simple fluid dynamics.

That flow restriction comes from the filter & engine flow paths. Anytime there is flow across a restriction, there will be a produced pressure differential (aka, PSID).

If you accurately measured the PSID across an oil filter and across the engine, you will definitely see PSID any time there is oil flow. The level of PSID will be determined by 3 factors: flow volume, fluid viscosity and the fixed flow resistance factor of the flow circuit. The PSID will be maximum at pump relief, and zero when the pump is off.

 

[BuickGN]

Originally Posted By: SuperBusa
Originally Posted By: Gary Allan
It's pretty simple. Below the relief level (that is seen at the pump) ..there is no such thing as a restriction. Assuming that the pump is of reasonable efficiency, the fluid will merely accelerate and will evidence a "pressure elevation" upstream of the choke.


See red text above. Technically, even when the pump is not in relief mode there is still "restriction". That flow restriction is what causes the pump to produce pressure at the volume it's putting out. If there was no restriction downstream of the pump, then the pump's output pressure would be near zero. The higher the restriction, the higher the pressure is required to force X gpms down the flow path. Simple fluid dynamics.

That flow restriction comes from the filter & engine flow paths. Anytime there is flow across a restriction, there will be a produced pressure differential (aka, PSID).

If you accurately measured the PSID across an oil filter and across the engine, you will definitely see PSID any time there is oil flow. The level of PSID will be determined by 3 factors: flow volume, fluid viscosity and the fixed flow resistance factor of the flow circuit. The PSID will be maximum at pump relief, and zero when the pump is off.


There are restrictions but volume remains the same regardless, below bypass. But you already know that.

I've enjoyed yours and Gary's posts in the other sections even though you two agree more than you disagree but neither will admit it.

 

[SuperBusa]

Originally Posted By: BuickGN
Originally Posted By: Brian_Bowers
English? If I'm understanding you correctly, then why wouldn't the pump always pump at the relief spring pressure at idle? Meaning shouldn't I always see 52 psi?


Simple answer: It's not spinning fast enough.

Once the rpms come up the pump has more volume than the relief circuit can deal with which results in the pressure above the relief setting.

I'm sure Gary will have a much more detailed answer. I always have to read those posts 2-3 times but usually come out with some good info.


Yep ... here's a flow vs. RPM chart showing how a positive displacement oil pump behaves. This is for an ideal pump with a relief valve that will regulate the pump's output pressure perfectly.

In the real world, the curve would not be straight, but arch over as the RPM increased due to pumping inefficacies, and the point where the relief valve came in would cause the curve to knee over quite fast, but not to a perfectly straight line to hold the output pressure and volume at a constant. That's why many guys with HV oil pumps will see oil pressures well above the pressure relief setting of the oil pump. The flow resistance of the engine they put the HV oil pump on will also have a factor in this phenomenon. If you put a HV oil pump meant for a V12 Allison with a pressure relief setting of 80 on a Honda Civic (with much more flow restriction), then the pump's relief circuit would have to work much harder and cause the actual relief pressure to be well above 80 because it couldn't shunt all the excess oil back to the sump. But on the engine the HV was mean for, maybe it would regulate right at 80 psi or a hair above. HV pump designers need to design the HV pump to match the engine application to make it work right.

 

[SuperBusa]

Originally Posted By: BuickGN

There are restrictions but volume remains the same regardless, below bypass. But you already know that.


You mean pump relief, right?

I've tired to use the term "relief" (and better yet "pump relief" or "pump relief mode") to mean pressure relief of the oil pump. The term "bypass" is used to refer to the filter's bypass valve. Technically, the pump's relief valve is not a bypass valve, but a shunt valve. It causes a change in flow volume output from the pump. On the other hand, the filter's bypass valve just "bypasses" flow around the filtering element ... but it allows ALL the flow entering the filter to exit the filter.

Originally Posted By: BuickGN
I've enjoyed yours and Gary's posts in the other sections even though you two agree more than you disagree but neither will admit it.

... well, I hope it's more than entertainment - would you rather we don't agree so much?

It's been good as far as bringing all this stuff to light in pain staking details to try and get everyone on the same page and to understand what's going on in an oil system. I think Gary has come my way more than he thinks.

I got into this thread kind of late ... so need to read from the beginning, but I'm afraid to in case I have to make all kinds of inputs.

 

[SuperBusa]

Originally Posted By: Brian_Bowers
So... if at idle the oil pump doesn't provide enought excess flow to reach relief a more restrictive oil filter would indeed reduce system pressure correct? FYI part #3 on the diagram is the pressure sending unit.


Anytime the pump is NOT in relief mode, you will have the same engine pressure gauge reading (at same oil visocity and engine RPM conditions of course), regardless of the filer's restriction. Only AFTER the pump has gone into relief mode will be able to tell if one filter is more restrictive than another. I gave more details in this thread.

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1525335#Post1525335

 

[BuickGN]

Originally Posted By: SuperBusa
Originally Posted By: BuickGN

There are restrictions but volume remains the same regardless, below bypass. But you already know that.


You mean pump relief, right?

I've tired to use the term "relief" (and better yet "pump relief" or "pump relief mode") to mean pressure relief of the oil pump. The term "bypass" is used to refer to the filter's bypass valve. Technically, the pump's relief valve is not a bypass valve, but a shunt valve. It causes a change in flow volume output from the pump. On the other hand, the filter's bypass valve just "bypasses" flow around the filtering element ... but it allows ALL the flow entering the filter to exit the filter.

Originally Posted By: BuickGN
I've enjoyed yours and Gary's posts in the other sections even though you two agree more than you disagree but neither will admit it.

... well, I hope it's more than entertainment - would you rather we don't agree so much?

It's been good as far as bringing all this stuff to light in pain staking details to try and get everyone on the same page and to understand what's going on in an oil system. I think Gary has come my way more than he thinks.

I got into this thread kind of late ... so need to read from the beginning, but I'm afraid to in case I have to make all kinds of inputs.

Understood. I meant pump bypass, I'm not very well written lol.

You guys going back and forth has taught me a lot. I've always run a high volume pump even though the fast guys told me not to. This was in an attempt to raise my idle pressure which it didn't help much, it just put me on the pump bypass at 3,000rpm instead of 4,500rpm. Now it makes more sense to run my stock pump and save the front cam bearing.

 

[Gary Allan]

Quote:
I think Gary has come my way more than he thinks.

Well, I'd say Gary has made concessions for the obscure things you seem to feel are important. While you've never quite come to grips with some things that are counter to your take on things

Some just can't willfully do that.

 

[SuperBusa]

Originally Posted By: Brian_Bowers
I'm trying to determine if removing the oil cooler actually caused my oil pressure at idle to go down, but when I first checked it back in Feb/Marh I may have not been looking at it at full hot.


Do you have a schematic or details on exactly how the oil cooler is plumbed into the oiling system? I have an 02 Z06, but never have had any reason to find out.

Were ever it is connected, it has to be a parallel flow circuit to the engine. This means that it takes part of the total volume of oil that enters the engine circuit after going through the oil filter. If that's the case, then removing it would cause that same fixed flow volume (when pump is NOT in relief) to go through a more restictive circuit and should cause the oil pressure to increase, not decrease. Humm ....

 

[Gary Allan]

Originally Posted By: BuickGN
Originally Posted By: SuperBusa
Originally Posted By: BuickGN

There are restrictions but volume remains the same regardless, below bypass. But you already know that.


You mean pump relief, right?

I've tired to use the term "relief" (and better yet "pump relief" or "pump relief mode") to mean pressure relief of the oil pump. The term "bypass" is used to refer to the filter's bypass valve. Technically, the pump's relief valve is not a bypass valve, but a shunt valve. It causes a change in flow volume output from the pump. On the other hand, the filter's bypass valve just "bypasses" flow around the filtering element ... but it allows ALL the flow entering the filter to exit the filter.

Originally Posted By: BuickGN
I've enjoyed yours and Gary's posts in the other sections even though you two agree more than you disagree but neither will admit it.

... well, I hope it's more than entertainment - would you rather we don't agree so much?

It's been good as far as bringing all this stuff to light in pain staking details to try and get everyone on the same page and to understand what's going on in an oil system. I think Gary has come my way more than he thinks.

I got into this thread kind of late ... so need to read from the beginning, but I'm afraid to in case I have to make all kinds of inputs.

Understood. I meant pump bypass, I'm not very well written lol.

You guys going back and forth has taught me a lot. I've always run a high volume pump even though the fast guys told me not to. This was in an attempt to raise my idle pressure which it didn't help much, it just put me on the pump bypass at 3,000rpm instead of 4,500rpm. Now it makes more sense to run my stock pump and save the front cam bearing.



Higher volume is only good if you can handle lower visc to allow it to fit through the engine. There you're using it more for cooling. That's what the current school of thought is with the race engine builders. They went high volume (relative) lower pressure. They figure 40% of engine cooling is done by the oil.

 

[SuperBusa]

Originally Posted By: Gary Allan
Quote:
I think Gary has come my way more than he thinks.

Well, I'd say Gary has made concessions for the obscure things you seem to feel are important. While you've never quite come to grips with some things that are counter to your take on things

Some just can't willfully do that.

What you can’t do is address and consider the possible operating conditions and consequences in the oiling system that are not typically experienced by Grandma driving the Buick to church ... unless she fires it up on a -10 deg F day and floors it thinking she instead had her foot on the brake.

I still believe you are not seeing the true physics going on in the oiling system and filters sometimes. But we can address those when they surface again in the future.

 

[BuickGN]

Originally Posted By: Gary Allan
Originally Posted By: BuickGN
Originally Posted By: SuperBusa
Originally Posted By: BuickGN

There are restrictions but volume remains the same regardless, below bypass. But you already know that.


You mean pump relief, right?

I've tired to use the term "relief" (and better yet "pump relief" or "pump relief mode") to mean pressure relief of the oil pump. The term "bypass" is used to refer to the filter's bypass valve. Technically, the pump's relief valve is not a bypass valve, but a shunt valve. It causes a change in flow volume output from the pump. On the other hand, the filter's bypass valve just "bypasses" flow around the filtering element ... but it allows ALL the flow entering the filter to exit the filter.

Originally Posted By: BuickGN
I've enjoyed yours and Gary's posts in the other sections even though you two agree more than you disagree but neither will admit it.

... well, I hope it's more than entertainment - would you rather we don't agree so much?

It's been good as far as bringing all this stuff to light in pain staking details to try and get everyone on the same page and to understand what's going on in an oil system. I think Gary has come my way more than he thinks.

I got into this thread kind of late ... so need to read from the beginning, but I'm afraid to in case I have to make all kinds of inputs.

Understood. I meant pump bypass, I'm not very well written lol.

You guys going back and forth has taught me a lot. I've always run a high volume pump even though the fast guys told me not to. This was in an attempt to raise my idle pressure which it didn't help much, it just put me on the pump bypass at 3,000rpm instead of 4,500rpm. Now it makes more sense to run my stock pump and save the front cam bearing.



Higher volume is only good if you can handle lower visc to allow it to fit through the engine. There you're using it more for cooling. That's what the current school of thought is with the race engine builders. They went high volume (relative) lower pressure. They figure 40% of engine cooling is done by the oil.


I still have a hard time accepting that school of thought. I can see how 40% of the cooling may come from oil. But I have a few problems with the theory, maybe you can poke some holes in it.

Wouldn't that heat come mostly be from the piston crown bottoms and from flowing over the heads and not bearings??

Suppose a thicker oil flows slower through a bearing but there's always a continuous flow, wouldn't the thicker oil just get hotter but still carry away the same amount of heat?

If the pump pressure is just to deliver flow to the bearings and the the hydrodynamic wedge motion takes over, wouldn't the same amout of oil "flow" thorough the bearing regardless of viscosity?