Cooler engine temps with higher viscosity?!

[JT20]

pretty much, which obviously is much less reliable and more viscosity/temp defendant than the other and this is a case where both scenarios are true respective to each other

That's the thing that always confused me, is just how splash lubrication works. My understanding is that pressurized oil (quote) exists, basically like you said:

1. When maintaining its film shape, and keeping one thing from touching another, i.e. a bearing from touching a rotating assembly, like at the bottom of a piston.
2. Through oil return holes.
3. In the cylinder walls. Some people still try to say that if an oil is too thick it won't fit.

All of these, you have the oil being shoved forcefully from one place to the next and it makes pressure.

Splash lubrication.. it is just waiting on gravity return? Does not seem like very good lubrication (like springs in a valve cover where there is oil in there but has no real direction. Seems like it just gets hot without doing anything.)

 

[ABN_CBT_ENGR]

That's the thing that always confused me, is just how splash lubrication works.

Literally, take a spoon, paddle or a dip (submerge) and throw the oil, that's splash lubrication.

The trick is making sure the volume and frequency of the splash maintains the necessary volume for the rolling parts to generate the wedge.

If it does, you're good- if not, you got problems

 

[demarpaint]

If its designed properly and within tolerance it "will" LOL- its when things get to the edge of those parameters when "should" walks in the door

It looks like we agree.........

 

[ABN_CBT_ENGR]

It looks like we agree.........

I see you been there before, LOL

 

[demarpaint]

I see you been there before, LOL

 

[ZeeOSix]

Through the galleries yes, but the oil on the heated internal components (valve train, pistons, cylinder walls) is not under pressure, and this is where viscosity is a factor in the rate at which it returns to the sump to be cooled.
No one is worrying, I just had an contradictory observation that I was hoping someone could explain through experience.

More true when the oil is cold vs fully hot ... but the whole engine is cold when the oil is cold so the engine doesn't really need cooling, it needs heating.

The oil "flow" and the "flow back time to the sump" when the oil (regardless of viscosity) is fully hot is hair splitting.

 

[ZeeOSix]

One of the basic things I learned is that it is only pressurized oil that can do any lubricating while an engine is running. This discussion seems to be building on that.

Splash oiling (ie, oil just getting on parts) is also providing lubrication. Many parts in an engine are splash lubricated.

 

[JT20]

Splash oiling (ie, oil just getting on parts) is also providing lubrication. Many parts in an engine are splash lubricated.

Well it appears I can fine-tune my understanding.

The splash lubrication, it gets where it needs to go reliably? Or are these the parts that suffer under high G's/cornering vs the film parts (or are they stressed equally)

 

[ZeeOSix]

Its true that viscosity affects MOFT but that's fluid specific so it plays more of a part on the top end where the main source of lubrication delivery is flow. In the other areas where the pump is driving the fluid to give a full fluid film, the pump's supply volume "should" overcome any thermal issue related to fluid film thickness and density.

Not sure what you're driving at with the first sentence in your quote. Maybe you can elaborate.

Re: the bolded statement. Journal bearings are "force feed" oil volume by the oil pump, but it's inside journal bearings where the oil is compressed, sheared and heated pretty significantly which directly effects the bearing MOFT. On a side note, this is why HTHS measurements were invented to get a measure of how the oil would react in journal bearings.

Journal bearings are one main area in the engine where oil viscosity and MOFT can make a difference in wear protection. The full film hydrodynamic oil wedge in the journal bearings is not created by the oil pump feed pressure, it's solely created by the interaction of the bearing geometry, rotational speed and the oil viscosity. If you feed oil to a journal bearing simply by gravity instead of a PD pump, the bearing would still build the same oil wedge and MOFT. It's true that the oil pump (if designed properly) will make the bearing flow more volume up and beyond what it would naturally flow from it's gravity feed rotation, and that extra oil volume flow can help keeping the oil temperature down inside the bearing.

The new cars with variable displacement oil pumps try to cut back the oil flow to the oiling system as much as possible to save 0.0001 MPG from PD pumping loss impact on fuel mileage. But I'm wondering how much that effects engine wear in the long run if they're on the hairy edge of lack of proper lubrication - ??

 

[mahanddeem]

I noticed higher oil temp (OBD ECU live data) using new(ner) formulation of PUP 5w30 (SN vs SN+). Which makes me believe than thinner oils tend to run hotter generally.

 

[JT20]

Not sure what you're driving at with the first sentence in you quote. Maybe you can elaborate.

Re: the bolded statement. Journal bearings are "force feed" oil volume by the oil pump, but it's inside journal bearings where the oil is compressed, sheared and heated pretty significantly which directly effects the bearing MOFT. This is one main area in the engine where oil viscosity and MOFT can make a difference in wear protection. The full film hydrodynamic oil wedge in the journal bearings is not created by the oil pump feed pressure, it's solely created by the interaction of the bearing geometry, rotational speed and the oil viscosity. If you feed oil to a journal bearing simply by gravity instead of a PD pump, the bearing would still build the same oil wedge and MOFT. It's true the the oil pump will make the bearing flow more volume up and beyond what it would naturally flow from it's gravity feed rotation, and that extra oil volume flow can help keeping the oil temperature down inside the bearing.

The new cars with variable displacement oil pumps try to cut back the oil flow to the oiling system as much as possible to save 0.0001 MPG from PD pumping loss impact on fuel mileage. But I'm wondering how much that effects engine wear in the long run if they're on the hairy edge of lack of proper lubrication - ??

Then there has always been the question about the actual rate of flow vs the pressure.. i.e. specifically, the oil pressure can be at the minimum, yet providing more flow and hence lubrication, than perhaps higher pressured oil. Like the oil pressure in an ICE. May not need to run at its maximum, or even mid pressure.. but, anything above the minimum, and if more oil (volume of oil?) "flow" is being delivered at the lower pressure.. then may be more beneficial.

Apologies if any of that came out wrong, I am trying to combine the old video example I have seen of a water hose, where pressure is created by putting your thumb over what comes out, but there is more volume of water flowing without the thumb over the output, and the arguments of those advancing or seeking to advance that thinner oil is the better choice in lubricating an engine.

 

[ZeeOSix]

Then there has always been the question about the actual rate of flow vs the pressure.. i.e. specifically, the oil pressure can be at the minimum, yet providing more flow and hence lubrication, than perhaps higher pressured oil. Like the oil pressure in an ICE. May not need to run at its maximum, or even mid pressure.. but, anything above the minimum, and if more oil (volume of oil?) "flow" is being delivered at the lower pressure.. then may be more beneficial.

Apologies if any of that came out wrong, I am trying to combine the old video example I have seen of a water hose, where pressure is created by putting your thumb over what comes out, but there is more volume of water flowing without the thumb over the output, and the arguments of those advancing or seeking to advance that thinner oil is the better choice in lubricating an engine.

The oiling system in an ICE is not like your house water system feeding your garden hose. With a PD oil pump (assuming the pump is 100% efficient) there will be the same exact oil flow volume at X engine RPM with 0W-16 as it will be with 20W-50. In general, it seems like the understanding of engine oiling systems is often misunderstood because people don't fully understand how a PD oil pump works in an ICE oiling system. Same thing with the understanding of oil filter delta-p discussions, etc.

If the engine is running at a constant 2000 RPM the oil flow volume will be exactly the same regardless of the oil viscosity. But as the oil warms up the pressure will slowly go down because it takes less output pressure on the pump to force the same exact flow volume through the oiling system. That's why the oil pressure is always lower at say idle when the oil is hot vs when cold. The oil flow volume leaving the PD pump is a direct function of engine RPM, and the pressure seen on the gauge is a function of engine RPM and oil temperature (viscosity).

 

[ABN_CBT_ENGR]

Not sure what you're driving at with the first sentence in your quote. Maybe you can elaborate.

Taking a very complex and widely misunderstood subject and condensing it knowing full well a degree of accuracy and understanding will be lost making a point on a different subject being discussed.

Journal bearings are "force feed" oil volume by the oil pump, but it's inside journal bearings where the oil is compressed, sheared and heated pretty significantly which directly effects the bearing MOFT. This is one main area in the engine where oil viscosity and MOFT can make a difference in wear protection.

That's not entirely correct but very close- the pumped fluid adds a degree of density to the fluid ( as compared to a static state) similar to "critical mass" so when the forces act inside the bearing the fluid film of acting like a true solid and is a few mils dense. Depending on the fluid density, pump force ( and a few other things) a less viscous fluid can make the same wedge against the same load. ( all other parameters equal)

This is done all the time and not unique to an ICE.

Like you said, manufacturers do this to reduce parasitic loads for that .0000000 whatever MPG- has nothing to do with lubricity other than they are trading one off for the other knowing they have to compensate otherwise they will blow the engine.

If you feed oil to a journal bearing simply by gravity instead of a PD pump, the bearing would still build the same oil wedge and MOFT.

True to a point but not past that point. There must be the tolerance to allow the volume to be compressed to maintain the MOFT as required by the load/RPM regardless of the feed method but that's really a sidebar subject.

I fully concur with the rest of your statement as written.

 

[Schwifty]

I noticed higher oil temp (OBD ECU live data) using new(ner) formulation of PUP 5w30 (SN vs SN+). Which makes me believe than thinner oils tend to run hotter generally.

From what I have seen argued is that the thinner oil runs over the hot components at a higher rate and does not stick around on those components as long, thus removing more heat from those components.

 

[ZeeOSix]

If you feed oil to a journal bearing simply by gravity instead of a PD pump, the bearing would still build the same oil wedge and MOFT.

True to a point but not past that point. There must be the tolerance to allow the volume to be compressed to maintain the MOFT as required by the load/RPM regardless of the feed method but that's really a sidebar subject.

My point was that the oil feed pressure to the bearing from the PD pump does not have any role in the resulting MOFT created inside the bearing. There is no supply pressure parameter involved in the design of a journal bearing. Only thing the supply pressure will do is cause slightly more flow through the bearing (above the bearing's flow from rotation) which can help keep the oil temperature down, which will help keep viscosity up slightly inside the bearing.

Hydrodynamic journal bearing [SubsTech]

www.substech.com

 

[ABN_CBT_ENGR]

My point was that the oil feed pressure to the bearing from the PD pump does not have any role in the resulting MOFT created inside the bearing. There is no supply pressure parameter involved in the design of a journal bearing. Only thing the supply pressure will do is cause slightly more flow through the bearing (above the bearing's flow from rotation) which can help keep the oil temperature down, which will help keep viscosity up slightly inside the bearing.

Hydrodynamic journal bearing [SubsTech]

www.substech.com

Don't need the link, I can write a book on the subject and probably know this as good as he does.

And this is not to impugn you in any way- this is a very complex subject and 99% of the people out there never encounter it in detail

This is an ultra fine point ( and crank bearings are a known special case not addressed in his article- they also have their own rules).

As you posted what you posted- that's 100% true but its incomplete and misleading due to all the special cases which must happen for it to be true and maintain trueness during the entire single cycle. ( and cant be explained in 3 lines)

This applies to a reciprocating application ( the special case)

Yes the bearing internals generate the pressure for the MOFT however the precursor is the pump ( in terms of volume and velocity) "pre-compress" the fluid in the pipe on the way there so its ready for the load zones unique to the tangential forces encountered under a loaded reciprocating action. ( this is the detailed part the internet articles don't touch)

If this did not happen, first the "slapping' of the bearing during the arc would simply "squirt" the oil back out so the boss tolerances act first as a shield ( to contain the moment) then the pump keeps force on the other end.

This is why during a failure analysis when the MOFT goes the impact looks like a half moon in path ( the textbook sign)

Even this brief bullet is leaving out a lot

This is not a shaft bearing where loading is constant ( which is the simplest form and whats commonly out there)

 

[ZeeOSix]

Yes the bearing internals generate the pressure for the MOFT however the precursor is the pump ( in terms of volume and velocity) "pre-compress" the fluid in the pipe on the way there so its ready for the load zones unique to the tangential forces encountered under a loaded reciprocating action. ( this is the detailed part the internet articles don't touch).

If you study journal bearings a bit more you'll see that the relatively measly 30~40 PSI of oil pressure (with hot oil) at the supply hole to the bearing doesn't do anything in terms of adding MOFT. That's my point ... oil pump pressure has no real effect on the MOFT inside a journal bearing - the local oil viscosity and geometry and rotational speed of the bearing is what determines the resulting MOFT. If you can supply links that distinctly shows otherwise then I'd be happy to read about it.

 

[ABN_CBT_ENGR]

If you study journal bearings a bit more you'll see that the relatively measly 30~40 PSI of oil pressure (with hot oil) at the supply hole to the bearing doesn't do anything in terms of adding MOFT. That's my point ... oil pump pressure has no real effect on the MOFT inside a journal bearing - the local oil viscosity and geometry and rotational speed of the bearing is what determines the resulting MOFT. If you can supply links that distinctly show otherwise then I'd be happy to read about it.

I didn't disagree with that, I thought I made that clear. I don't recall using the word pressure in any context relative to what I said

 

[ZeeOSix]

I didn't disagree with that, I thought I made that clear. I don't recall using the word pressure in any context relative to what I said

That's not entirely correct but very close- the pumped fluid adds a degree of density to the fluid ( as compared to a static state) similar to "critical mass" so when the forces act inside the bearing the fluid film of acting like a true solid and is a few mils dense. Depending on the fluid density, pump force ( and a few other things) a less viscous fluid can make the same wedge against the same load. ( all other parameters equal)

You can't have "pump force" without a resulting oil pressure. A less viscous oil will have a smaller wedge (ie, less MOFT) with all other parameters equal, regardless of the supply pressure (which doesn't effect MOFT). You're implying that pump force (oil supply pressure) can result in a less viscous oil to have the same MOFT wedge. If you can post links showing this in context of an ICE it would be helpful for clarification of your viewpoint.

 

[ABN_CBT_ENGR]

You can't have "pump force" without a resulting oil pressure. A less viscous oil will have a smaller wedge (ie, less MOFT) with all other parameters equal, regardless of the supply pressure (which doesn't effect MOFT). You're implying that pump force (oil supply pressure) can result in a less viscous oil to have the same MOFT wedge. If you can post links showing this in context of an ICE it would be helpful for clarification of your viewpoint.

You have absolutely no significant knowledge of this subject at all or fluid dynamics or anything else relative to what I was talking about so I doubt you would understand a link if it were sent.

I am trying to be nice but you just drone in a circle and manipulating what I said into something I didn't say then arguing it.

The simple fact you are arguing against well known tenets of engineering is by itself proof positive you don't have a detailed knowledge of the subject or the conditions surrounding it.

I will be happy to explain it but if you don't grasp what has already been posted then you certainly wont grasp a more detailed explanation.

So, go back and put what I said IN CONTEXT and then raise a legitimate question.

Don't change it around and don't interpret it- just understand it.

I'll be happy to comply but you will have to advance yourself in a few areas to deep dive in this