Explain straight weight oil viscosity recommendations to me, please.

[FlyingDude]

On 6/3/2022 at 11:36 PM, carusoam said:

11) Selecting a more viscous oil over a less viscous oil…. Can affect your gas mileage…

How does that work?

[Pinecone]

5 hours ago, A64Pilot said:

A piston isn’t pressure lubricated, only the bearings etc are. Pistons and rings of course are splash lubricated and do fine because the loads are low, and yes even on the splash lubricated parts the oil film prevents direct metal to metal contact. Splash lubrication works fine so long as the loads are low it’s when the loads increase that pressure is required

If you don’t believe pressure is important, then why do modern engines require a min pressure, and what happens if you run with less than min? As an engine wears the pressure drops, volume of oil flow is the same, but when the pressure drops below min metal to metal contact is made and that can lead to galling and a spun bearing from a lack of pressure, not flow as it is the same, but pressure. This is a hydraulic system and as fluids are incompressible at a given engine RPM the flow is steady 

Engines are run every day with no pressure at all, lawnmower engines as an example the small cheap motors are splash lubricated, all old car motors were too.

Pressure is what drives changes in oil viscosity, it’s temperatures effect on pressure is why temp is used as the indicator for when to change viscosity, viscosity, pressure and flow are interrelated of course.

Higher viscosity oil can provide better protection in cases, our cams for instance which are splash lubricated, the thicker oil can help prevent metal to metal contact.

The “most wear occurs on start up” due to lack of lubrication is sort of a myth and was dispelled decades ago by pre-lubrication systems that established both oil pressure and flow before an engine ever turned. If lack of oil oil pressure and flow on start up was the primary wear mechanism then a pre lubricated engine should have greatly extended life, but unfortunately it didn’t happen. I wish it had because there are several ways to make a pre-lubrication system that’s not complex or expensive, and who wouldn’t want to extend an engines life?

You keep saying that much is lubricated with splash and that some engines are entirely splash lubricated, then say that oil pressure is super important.  

The reason low oil pressure is a problem is that you are not sure that the oil is getting to all the places it needs to get (bearings mainly) as when the engine wears and the oil pressure drops, the oil is not be pushed through all the passages.  It is flowing out of the first location it comes to.

But the oil pressure from the pump is NOT what keeps the bearings from running metal to metal.  The pressure gets the oil TO the bearings.

[jaylw314]

I thought the move to multiweight oils was mainly for the consumer auto market.  By people not having to discard oil between seasons, waste oil is reduced.  The consumer auto market is large enough that the sheer volume of waste oil has a significant economic and ecologic impact.  I recall there was a PSA from a number of agencies about 20 years ago to "STOP CHANGING YOUR OIL EVERY 3000 MILES" for that reason, after the advent of all those drive-through oil change places that tried to scare people into excessively frequent oil changes.

That being said, I thought the resistance to multiweight oils for our planes was mainly lead incompatibility with synthetic multiweight oil.  I'm not sure how modern MW oils overcome that, but I assume they have for Aeroshell and Phillips MW oils?

For our motors, we SHOULD be changing our motor oil at least every season, so why not just change oils based on the seasons if need be?

 

Edited June 6, 2022 by jaylw314

[Fly Boomer]

45 minutes ago, jaylw314 said:

we SHOULD be changing our motor oil at least every season, so why not just change oils based on the seasons if need be?

There are airplanes here that suffer 100 dF temperature swings on the ground in 24 hours, and a few of our favorite brand airplanes that are certificated up to 28,000 -- you can do the math for the adiabatic lapse rate.  Forget about seasons.

[carusoam]

7 hours ago, FlyingDude said:

How does that work?

In simple terms….

As much as oil is slippery stuff…

Viscosity is a measure of resistance to flow.

More viscous = more resistance.

 

So….

We want to select an oil with enough viscosity to lubricate the parts….

But, not go so far that it has more resistance than it needs…

of course, this resistance is probably in the order of a nmpg or so… not enough to be obvious….

 

In cold environments, it can take a few minutes to get the oil flowing… less viscous the better….

In hot environments, the oil can get so thin it no longer protects the metal surfaces enough….

Then there is the chemistry challenge… the oil breaks down above certain temps when held there over time….

 

Where Mooney engines see the oil break down challenge… exhaust valve guides, and turbo bearings….

Our oil is really stable at temps near 200°F and below… not so stable at temps near the EGT….   Keep the oil flowing, until the engine is as cool as it is going to get… often coolest right at touchdown…

If oil gets over heated in the valve guides… it turns into carbon deposits… deposits block the flow of oil, causing the oil to stay in the hot zone even longer… making more carbon deposits….

Reaming the valve guides is the method of removing carbon chunks out of the guide…

If you see carbon chunks in the shape of the valve guide and stem, gathering in you oil filter…. It may be time ream the guides…  

 

My old O360 was known for collecting carbon deposits from the exhaust valve guides…

 

Keep in mind…

OilT and OilP are being measured at the sensors… the rest of the engine is going to be different…

Having the OilT and OilP in the right zones guarantees that the oil is behaving as expected, and able to be getting to all the right places as expected…  it won’t say anything about local temps and pressures… or blockages…

PP thoughts only, not a mechanic…

Best regards,

-a-

[A64Pilot]

7 hours ago, FlyingDude said:

How does that work?

The thicker oil will cause more drag, more drag reduced milage.

Oil control, that is determining exactly where the oil gets to has become very important in high performance as in racing engines, keeping the oil only where it’s need frees up quite a bit of HP.

Even our old American V8’s often have windage trays around the crankshaft, the windage trays job is to keep the oil coming off of the crankshaft away from it to reduce drag most noticeably at high RPM.  Most truck motors etc don’t have windage trays. They may now, but back in the day the didn’t.

Modern “energy saving” motor oil has special anti friction modifiers in it to increase fuel milage, use those oils in a wet clutch motorcycle and the clutch will slip.

Energy conserving oils have a starburst on the label and can save 1% to 3% on fuel consumption

https://bobistheoilguy.com/forums/threads/tell-me-about-energy-conserving-oils.7420/

[A64Pilot]

3 hours ago, Pinecone said:

You keep saying that much is lubricated with splash and that some engines are entirely splash lubricated, then say that oil pressure is super important.  

The reason low oil pressure is a problem is that you are not sure that the oil is getting to all the places it needs to get (bearings mainly) as when the engine wears and the oil pressure drops, the oil is not be pushed through all the passages.  It is flowing out of the first location it comes to.

But the oil pressure from the pump is NOT what keeps the bearings from running metal to metal.  The pressure gets the oil TO the bearings.

If you would read my post I was making the point that an engine with light bearing loads can run just fine with splash lubrication, but the higher the loading, the more oil pressure required.  Highly loaded engines require relatively high pressure, lower bearing loads require less. My Mooney runs 80 to 90 in cruise maybe, my C-85 in my little Cessna runs 35 or so, less than half, both numbers are fine, the bearing loading is higher on the Lycoming than the little Conti.

[A64Pilot]

The purpose of a multi viscosity oil is to maintain viscosity through out a wide temperature range, in the case of Aeroshell’s 15W-50 oil, it’s a 15W oil with Viscosity Improvers that keep it from thinning out as it gets hot. So when hot it acts like a 50W oil. Multi viscosity oils are often not  Synthetic although with the Castrol lawsuit years ago even the definition of what synthetic means has changed. Many “Synthetics” now are 100% mineral oil. Advertising lies.

http://www.1st-in-synthetics.com/a_defining_moment_for_synthetics.htm

There are many additive packages in modern oil, however the VI (viscosity improver) package is among the first to degrade, but not for way more than 50 hours. In a properly running and maintained aircraft engine we change oil not because the oil has broken down or worn out, but because it’s full of garbage, lead and carbon etc. Our engines don’t run as clean as a Modern auto engine. People want to think they average 50 or 60 MPH in their cars but they don’t average is often in the 20’s and city dwellers even lower, that time sitting at red lights, stopping in traffic etc kills average speed, but anyway a good auto oil can likely last 10,000 miles and at an average speed of 20 thats 500 hours or ten times as long as our airplanes. 50 hours is nothing to an oil, but we change early to get the junk out.

The absolutely best use of oil analysis is to determine the condition of the oil, but it’s been sold as an engine analysis and most don’t look for fuel dilution, viscosity, TBN or TAN etc. which of course tells you if your oil was still good or not. In my opinion I want it out before any degradation occurs.

Aeroshell’s 15W-50 is a syn blend as syn has numerous advantages, but it won’t hold lead in suspension so you need some non synthetic for that. 

Personally I change oil four times a year, as I fly about 100 hours a year that works out to about every 25 hours. That’s probably excessive, but It’s what I do.

Edited June 6, 2022 by A64Pilot

[jaylw314]

1 hour ago, A64Pilot said:

The purpose of a multi viscosity oil is to maintain viscosity through out a wide temperature range, in the case of Aeroshell’s 15W-50 oil, it’s a 15W oil with Viscosity Improvers that keep it from thinning out as it gets hot. So when hot it acts like a 50W oil. Multi viscosity oils are often not  Synthetic although with the Castrol lawsuit years ago even the definition of what synthetic means has changed. Many “Synthetics” now are 100% mineral oil. Advertising lies.

http://www.1st-in-synthetics.com/a_defining_moment_for_synthetics.htm

There are many additive packages in modern oil, however the VI (viscosity improver) package is among the first to degrade, but not for way more than 50 hours. In a properly running and maintained aircraft engine we change oil not because the oil has broken down or worn out, but because it’s full of garbage, lead and carbon etc. Our engines don’t run as clean as a Modern auto engine. People want to think they average 50 or 60 MPH in their cars but they don’t average is often in the 20’s and city dwellers even lower, that time sitting at red lights, stopping in traffic etc kills average speed, but anyway a good auto oil can likely last 10,000 miles and at an average speed of 20 thats 500 hours or ten times as long as our airplanes. 50 hours is nothing to an oil, but we change early to get the junk out.

The absolutely best use of oil analysis is to determine the condition of the oil, but it’s been sold as an engine analysis and most don’t look for fuel dilution, viscosity, TBN or TAN etc. which of course tells you if your oil was still good or not. In my opinion I want it out before any degradation occurs.

Aeroshell’s 15W-50 is a syn blend as syn has numerous advantages, but it won’t hold lead in suspension so you need some non synthetic for that. 

Personally I change oil four times a year, as I fly about 100 hours a year that works out to about every 25 hours. That’s probably excessive, but It’s what I do.

For the sake of pedanticness, I think the W stands for "Winter" not "weight"  

[jaylw314]

3 hours ago, Fly Boomer said:

There are airplanes here that suffer 100 dF temperature swings on the ground in 24 hours, and a few of our favorite brand airplanes that are certificated up to 28,000 -- you can do the math for the adiabatic lapse rate.  Forget about seasons.

I'm only talking about the temperature on startup.  As mentioned before, I think the outside temp's impact on running oil condition is small in comparison.  For perspective, multiweight Aeroshell 15w-50, which you'd use during cold weather starts, still targets SAE 50 when warm, precisely the same as your "summer" Aeroshell 100.

[A64Pilot]

33 minutes ago, jaylw314 said:

For the sake of pedanticness, I think the W stands for "Winter" not "weight"  

OK, I stand corrected then, I guess for straight weight oils you spell weight out as opposed to using W?

Even in hot weather as in todays 92F I find I get oil pressure quicker with the 15W-50 than I do with straight weight oils. So I’ve even taken to running 15W-50 in my 1946 Cessna. Some will argue it wasn’t designed for multi viscosity oil, but it wasn’t designed for 100 Octane fuel either, or maybe even metal propellors.

Edited June 7, 2022 by A64Pilot

[jetdriven]

3 hours ago, A64Pilot said:

If you would read my post I was making the point that an engine with light bearing loads can run just fine with splash lubrication, but the higher the loading, the more oil pressure required.  Highly loaded engines require relatively high pressure, lower bearing loads require less. My Mooney runs 80 to 90 in cruise maybe, my C-85 in my little Cessna runs 35 or so, less than half, both numbers are fine, the bearing loading is higher on the Lycoming than the little Conti.

The Lycoming oil pressure value is read right off the oil pump.  The Continental oil pressure reading is taken off the furthest end of the cam gallery.  They’re probably closer than you think. 

[Pinecone]

7 hours ago, A64Pilot said:

If you would read my post I was making the point that an engine with light bearing loads can run just fine with splash lubrication, but the higher the loading, the more oil pressure required.  Highly loaded engines require relatively high pressure, lower bearing loads require less. My Mooney runs 80 to 90 in cruise maybe, my C-85 in my little Cessna runs 35 or so, less than half, both numbers are fine, the bearing loading is higher on the Lycoming than the little Conti.

Nope  Oil pressure has nothing to go with the pressure on the oil at the bearing point.

Let's see, combustion chamber pressure is 300 to 1000 psi.  So, how does an 80 psi oil pressure hold the parts away from each other.  Now, add in that the area of the piston of a simple O/IO-360 is 20.62 square inches, so the total force on the connection rod is 6,200 to 20,600 pounds.  And the bearing area is how big?  Even if it is 10 square inches, that is still 620 to 2,060 psi.

Again, how is your 80 psi oil pressure handling that load?

It doesn't.  The rotary motion creates a wedge of oil, at the required pressure, to keep metal to metal contact from occurring.

A railroad car axle bearing is not pressure lubricated.  The lower part rotates in a bath of oil at 0 pressure.  The bearing area is only on top (only downward loads), but the oil film prevents metal to metal contact due to the induced oil wedge.  BTW the bearing loads on a loaded railroad car axle bearing is MUCH higher than our engine bearing loads.

 

We measure oil pressure to ensure the oil is delivered where it is needed.  That is all.

Edited June 7, 2022 by Pinecone

[jaylw314]

7 hours ago, A64Pilot said:

OK, I stand corrected then, I guess for straight weight oils you spell weight out as opposed to using W?

Even in hot weather as in todays 92F I find I get oil pressure quicker with the 15W-50 than I do with straight weight oils. So I’ve even taken to running 15W-50 in my 1946 Cessna. Some will argue it wasn’t designed for multi viscosity oil, but it wasn’t designed for 100 Octane fuel either, or maybe even metal propellors.

AFAIK, the 'weight' is the same as 'SAE grade'.  The confusing part is that there's normal and winter oil SAE grades, and the winter oil grades end in W.  15W-50 oil has to meet the specs for both SAE 15W and 50.

From wikipedia:

A single-grade engine oil, as defined by SAE J300, cannot use a polymeric viscosity index improver (VII, also viscosity modifier, VM) additive. SAE J300 has established eleven viscosity grades, of which six are considered Winter-grades and given a W designation. The 11 viscosity grades are 0W, 5W, 10W, 15W, 20W, 25W, 20, 30, 40, 50, and 60. In the United States, these numbers are often referred to as the "weight" of a motor oil, and single-grade motor oils are often called "straight-weight" oils.[13]

For single winter grade oils, the dynamic viscosity is measured at different cold temperatures, specified in J300 depending on the viscosity grade, in units of mPa·s, or the equivalent older non-SI units, centipoise (abbreviated cP), using two different test methods. They are the cold-cranking simulator (ASTM D5293) and the mini-rotary viscometer (ASTM D4684). Based on the coldest temperature the oil passes at, that oil is graded as SAE viscosity grade 0W, 5W, 10W, 15W, 20W, or 25W. The lower the viscosity grade, the lower the temperature the oil can pass. For example, if an oil passes at the specifications for 10W and 5W, but fails for 0W, then that oil must be labeled as an SAE 5W. That oil cannot be labeled as either 0W or 10W.

For single non-winter grade oils, the kinematic viscosity is measured at a temperature of 100 °C (212 °F) in units of mm2/s (millimetre squared per second) or the equivalent older non-SI units, centistokes (abbreviated cSt). Based on the range of viscosity the oil falls in at that temperature, the oil is graded as SAE viscosity grade 20, 30, 40, 50, or 60. In addition, for SAE grades 20, 30, and 40, a minimum viscosity measured at 150 °C (302 °F) and at a high-shear rate is also required. The higher the viscosity, the higher the SAE viscosity grade is.

The crucial part is that W oils are spec'd by a cold test (I'm not sure what temp), while normal oils are spec'd by a hot test.  So 15W-50 means that in the cold test, it meets SAE 15W and at 100C it meets SAE 50

As far as I can tell, the W oils aren't spec'd while hot, and the normal oils aren't spec'd while cold.  I'd interpret that to mean there's no requirement for 15W-50 to function any differently than 50 oil at working temps.

[Shadrach]

On 6/4/2022 at 10:21 AM, A64Pilot said:

Pressure is at least as important as flow is, you can only run low viscosity oil if and only if you can maintain good pressure with it. Pressure is what keeps metal to metal contact from occurring in a high compression high power engine, back in the day of splash lubrication it worked as long as the loads were low but it’s what determined max power, that’s the reason why aircraft engines were put in early tanks, because of the pressure lubrication power levels could be higher. Auto engines of the time were splash lubricated.

Pressure is flow. If you sealed the system pressurized the lubricant at 0psi, 10psi, 300psi and so on it would make no difference.  The pressure exerted by moving engine parts on the oil exceeds pump pressure by many multiples. The pressure the rod is exerting on the crank is 1000s of PSI. The only thing separating the rod bearing from the crank pin is hydrodynamic pressure greater than that being exerted by the moving part.  Think about a cam lobes. They operate with zero oil pressure but with enough flow to maintain hydrodynamic film between lobe and lifter.

[A64Pilot]

Pressure is what reestablishes the cushion of oil, the higher the pressure, the quicker that cushion is reestablished. Pressure doesn’t equal flow because this is a hydraulic system and oil isn’t compressible. Think of a Pressure washer, with the nozzle removed the flow is the same as with it installed, but pressure goes from about 30 PSI to well over 1,000 PSI. But if it’s a 1 GPM pump, it’s pumping 1 GPM at either pressure. When an engine wears the pressure decreases because it’s just like that pressure washer it’s fixed volume, to increase pressure you restrict the opening until the pressure rises enough to equal the flow the pump makes, to decrease it you open up the restriction, a worn engine opens up the restrictions because tolerances are higher so pressure decreases. Volume remains the same. Pressure varies based on restriction, but flow is constant if RPM is constant. Thicker oil raises pressure because it increases the restriction

Now volume does in fact follow RPM as of course the lower pump speed decreases volume, and pressure drops due to decreased volume, so oil pressure will follow RPM until the relief valve opens where it should remain relatively constant.

Oil pressure functions similar to an airbag like in a car, the airbag has little pressure but inflates in a very short interval, and you smack into it in a very short interval and hit it with a great weight which is pressure, so for an instant it’s pressure goes very high, but as it’s a very short duration, the filled air bag stops you because when you smack it pressure rises to keep you from impacting the steering wheel, but it couldn’t hold that pressure for only a very short interval because it’s full of holes. if you wanted to keep hitting that air bag say 20 times per second, you need a significant pressure of air to refill it in time for the next hit. That’s the oil in your bearings the harder and faster you hit it, the higher the oil pressure needs to be to reestablish the cushion for the next hit

So far as pressure varying by a factor of three from beginning to end of the system, when you install an engine monitor and pick the pressure off of the front of the engine your saying you only see 30 PSI or so?

You will see lower oil pressures in parts of the system if there is a restrictor in that branch, but unless there are restrictions the pressure in the system should be pretty close from beginning to end. 

Pressure is relevant and pressure is required or we wouldn’t have low oil pressure limitations, and we would have stuck with splash lubrication.

Splash lubrication works but is a limiting factor in how much power an engine could make, Auto engines back in the day we just put bigger ones in for more power, but that doesn’t work well for aircraft so they got pressure lubrication first.

Trains 100 years ago did have plain bearings with “stuffing boxes” which had oil soaked rags in them to keep the plain bearings wet with oil, but they were pushing the limits and fires weren’t uncommon, the term “hot box” came from trains.

So they first went with ball bearings I believe because they couldn’t carry more weight with plain bearings and as weights continued to increase roller bearings replaced balls

Roller bearing crankshafts aren’t uncommon but are difficult and more expensive to manufacture.

Yes plain bearings are known as “hydrodynamic bearings” but the correct pressure is exceedingly important, because without it that hydrodynamic bearing will go metal to metal and when it does that a spun bearing is likely.

If you have ever built a race car motor you almost certainly put in a high volume oil pump to increase the oil pressure much higher than a stock motor, if pressure weren’t very important we wouldn’t have bothered, but increasing the volume to increase pressure allowed for much higher RPM before you spun a bearing. To increase pressure you either increased volume or decreased clearances, we ran at min clearances as is so volume had to go up to get higher pressure

 

[Fly Boomer]

16 minutes ago, A64Pilot said:

to increase pressure you restrict the opening until the pressure rises

So you are saying that Bernoulli was wrong, and that the increased speed of air over the top of a wing actually INCREASES pressure, driving the airplane down?  Also, the venturi on the side of many older airplanes actually INCREASED pressure to drive our vacuum instruments?

[A64Pilot]

15 minutes ago, Fly Boomer said:

So you are saying that Bernoulli was wrong, and that the increased speed of air over the top of a wing actually INCREASES pressure, driving the airplane down?  Also, the venturi on the side of many older airplanes actually INCREASED pressure to drive our vacuum instruments?

Use common sense, what happens when you put your thumb over the end of a garden hose and restrict the opening. 

Edited June 7, 2022 by A64Pilot

[Fly Boomer]

Just now, A64Pilot said:

Use common sense

Or a physics text.  Or the Internet.

[Shadrach]

20 minutes ago, A64Pilot said:

Use common sense, what happens when you put your thumb over the end of a garden hose and restrict the opening. 

restricting flow to increase pressure?

[EricJ]

I've invented a new battery charger:   Put a large resistor across it, sufficient to increase the voltage to recharge.    If it doesn't raise the voltage sufficiently, put a larger resistor across it.

Hint:  it doesn't work for water or oil or any other fluid, either.

 

[A64Pilot]

You guys seriously don’t understand that if you put your thumb over a flowing garden hose the pressure in the hose increases? Go try it.

Back to the pressure washer, use the soap nozzle, the pressure is low because there is little restriction, put the washer nozzle on instead, explain why the pressure goes through the roof, it’s because the hole is smaller and the restriction raises pressure.

You guys confuse yourselves by trying to make something simple complicated.

Bernoulli’s principle has nothing to do with this.

Edited June 7, 2022 by A64Pilot

[A64Pilot]

1 hour ago, Shadrach said:

restricting flow to increase pressure?

OK then explain why the pressure drops when the oil pressure relief valve opens.

This ought to be interesting

[Shadrach]

6 minutes ago, A64Pilot said:

OK then explain why the pressure drops when the oil pressure relief valve opens.

This ought to be interesting

Read what I wrote...again...carefully.

[EricJ]

2 hours ago, Shadrach said:

restricting flow to increase pressure?

Yeah, people get confused easily.

The only reason restricting flow will increase pressure at a certain point is because the reduction in flow is reducing the pressure drop across the previous upstream drop source(s).   There's no net increase in energy, unless the restriction is also a power source that adds energy somehow. 

Pressure is potential energy, so the only way to increase pressure at a particular point is to add energy.    One way to do that is to take it away (reduce consumption) from whatever is upstream, by reducing flow.   A pressure regulator works by controlling flow this way.    It doesn't create any pressure, the pump does that, it controls how much pressure drops across the regulator by controlling flow through it, so that the pressure on the output side remains as reasonably constant as possible (which regulates flow to the downstream system).    Pressure doesn't matter in a typical lubrication system if there's no flow.    If the oil is kept at a reasonably constant temperature (which is why we have a vernatherm and an oil cooler), then the flow load required will be reasonably constant, so the regulator just needs to provide sufficient (reasonably constant) pressure to service that flow load.