HTHS vis spec trumps the Kinematic 100C vis spec'

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This thread's got my brain itching!

Here are a few questions I have:

Can HTHS be artificially elevated with VII's, but breakdown of VII's results in loss of HTHS and kinematic viscosity?

Can HTHS be high due to the base oil used, and without VII's remain constant throughout service?

Given that density and HTHS are related figures, can we use density, HTHS and KV values to very roughly determine how much VII is used in a product?
 
Originally Posted By: Tempest
Quote:
Given that density and HTHS are related figures

Please provide some information to show this.


Originally Posted By: CATERHAM
Originally Posted By: Newtonville
I found wikipedias notes on "viscosity" interesting as well as this English site

http://www.kewengineering.co.uk/Auto_oils/oil_viscosity_explained.htm

It seems it is entering the realm of chemical engineering/fluid dynamics.

Basically I see dynamic and kinematic viscosity described, dynamic being kinematic divided by density. One is in cSt, other cP. In very complex molecules in solution with other complex molecules, or additives, tracking the density changes at temperatures, pressures, and shears would be challenging? Since HTHS test uses the same cP units as dynamic viscosity, as decribed on sites, aren't they one and the same? Is HTHS= dynamic viscosity at 150c?

Maybe Pennzoil's "adaptive molecules" are not to be made fun of so much after all.


Actually, dynamic viscosity is the kinematic viscosity times (not divided by) the oil's density. It doesn't equal the HTHS viscosity because it doesn't factor in the pressure-viscosity coefficients of different oil chemistries.
See the following paper, particularly page 8, which goes into some detail on the relationship between HTHS vis and dynamic vis:

http://www.kulikow.com/project/Literature/PEG-Esters/NoLowSAPEngineOil-JAI2008.pdf.pdf


I interpreted this to mean density as a factor in calculating dynamic viscosity of with it's relationship to HTHS being discussed in that paper. I don't mean that they are directly correlating. I'm just curious if we can use some of the data to determine (roughly) how VII dependent an oil is.
 
There is very little difference in density from a 20 grade to a 50 grade yet there will be a significant differences in HTHS. We can therefore determine that there are no meaningful correlations between density and HTHS.
 
Originally Posted By: Tempest
There is very little difference in density from a 20 grade to a 50 grade yet there will be a significant differences in HTHS. We can therefore determine that there are no meaningful correlations between density and HTHS.


True, at face value on the SAE grading scale, many oils don't vary much. Again, I'm just trying to use the relationship between viscosity and density to determine VII content and 'durability'.

Quote:

Mobil Delvac MX 15W-40
Density @ 15ºC kg/l, ASTM D 4052 0.879
HTHS @ 150ºC, cP, ASTM D4683 4.3

Mobil 1 0W-40
Density @15º C kg/l, ASTM D 4052 0.85

THS Viscosity, mPa•s @ 150ºC, ASTM D 4683 3.7
(will this HTHS drop dramatically as VII's shear?)


There is a huge difference in HTHS.
Can you guess which one is more shear stable (contains least VII )? Even starting with a significantly higher HTHS, I strongly suspect the Delvac MX will not only shear far less at the drain interval, but won't drop it's HTHS even close to that of the virgin 0w40!

Which brings me to my next observation. I've noticed base stock, (type and viscosity) and VII content have the most impact on density and HTHS. Density is not a meaningless value at all IMO. 0w20 and 0w40 may both be blended with identical light (albeit stable, synthetic) base stocks, share a densoty value and differ only in VII content. All being equal, the lower spread will shear less, and maintain it's HTHS. It should seem to be that the KV should be of the least value when determining the "robustness" of a finished product.


Here's are some properties of a unique 5w20 with outstanding performance:

Quote:

Redline 5w20
HTHS Vis, cP @150°C, ASTM D4741 3.3
Density: no longer published?! I recall 0.880-0.890 from previous investigation.


Redline oils are blended differently as far as I know. They start with a base stock that is closer to the viscosity of the finished product, relying on the base oil's natural VI and use little to no VII's for spread. Their oils have arguably THE highest densities of the "synthetic" oils. Now, I remember this from research a long time ago, and it appears the boneheads publishing the Redline litrature have removed their density ratings, including the MSDS. (seriously what is that about). All they have now is ONE specific gravity value for THE ENTIRE motor oil lineup in the MSDS. Does anyone know where I can find the density values for Redline now? I recall the 5w20 being somewhere in the 0.880-0.890 kg/l range which matches perfectly with it's HTHS (and shear stability), despite being a 20 grade.
 
Originally Posted By: addyguy
I do understand what you've said here, but I still think that it is a VERY valid argument that increasing the use of HT/HS specs is not useful at all due to the extreme environment that reading is taken in.

Think about the daily use MOST cars see - start up, putter 3-10 miles to work at low traffic speeds in average weather, with very little revs or throttle use at all. Oil will get warm, but nowhere near 150C.

Even if by some chance the oil DID get that hot, the other part of the equation is the stress part - HT/HS measures protection against heat and stress, usually from high revs. Not a factor in MOST daily driving scenarios.


Oil going trough the bearings or lubricating piston rings sound like a pretty extreme environment to me and it happens with every motor revolution!

What do you think temperature is in bearings and piston ring area?
 
Last edited:
Originally Posted By: river_rat
CATERHAM, can you post a OP vs published HTHS graph with R² correlation from Excel?


An interesting idea, but what I will provide is the raw data of some of the oils I've tested (feel free to play with the info').
All oil pressure readings were made at 6,500 rpm and oil temp' of 95C:

M1 5W-50 ..... KV100 17.5 cSt...HTHS 4.21 cP...OP 92 ...psi
M1 0W-40 ..... KV100 14.0 cSt...HTHS 3.7 .cP...OP 86 ...psi
RL 10W-30 .... KV100 11.0 cSt...HTHS 3.8 .cP...OP 87 ...psi
RL 5W-30 ..... KV100 10.6 cSt...HTHS 3.8 .cP...OP 87 ...psi
GC 0W-30 ..... KV100 12.2 cSt...HTHS 3.5 .cP...OP 83-84 psi
RL 5W-20 ..... KV100 9.1 cSt...HTHS 3.3 .cP...OP 80 ...psi
M1 5W-30 ..... KV100 11.3 cSt...HTHS 3.09 cP...OP 78 ...psi
PP 5W-30 ..... KV100 10.3 cSt...HTHS 3.1 .cP...OP 78 ...psi
RL blend, 3qts 5W-20 and 1qt 0W-10 race oil *
...............KV100 8.2cSt est HTHS 2.85 cP...OP 74 ...psi
Toyota (Nippon Oil) 0W-20 virgin, less than 30 miles on oil
...............KV100 8.8 cSt...HTHS 2.6 .cP...OP 71 ...psi
Toyota 0W-20 used with 150 miles on oil **
...........est KV100 8.0cSt est HTHS 2.4 .cP...OP 65 ...psi

* You can disregard the RL blend if you like as the KV100
spec' is calculated and the HTHS vis is an estimate only, from
RL.
** The high VI (214) Toyota oil lost oil pressure due to oil shear almost immediately in service and then stabilized which I believe must be by design as I've never seen oil shear so fast before. Consiquently I wanted to show the actual OP after just a few miles vs the virgin oil. Of course the KV100 and HTHS spec's are estimates for the used oil.

I would love to test more oils but I don't rack up much in the way of mileage so it's a long process unless I start changing out the oil at rediculously short oil change intervals.
I've corresponded with a few BITOG members who have oil pressure and oil temp' gauges in their vehicles and have encouraged them to start logging their OP readings.
Any other members with oil gauges I'd like to hear from you, so feel free to PM me.

I encourage all members to consider installing oil gauges, particularly those that have regular UOA's done. A set of oil gauges will provide a wealth of info that UOA simply can't provide and it's a one time expense unlike UOA's.
 
Very cool that you took such careful oil pressure measurements.

I plotted oil pressure vs KV@100C and the linear trendline's R-squared value was only 0.617 (not very good correlation).

The trendline for oil pressure vs HTHS viscosity had an R-squared value of 0.9852, which is quite good!

Note: I did not include the Red Line blend for the reason you said.
 
Originally Posted By: CATERHAM
Originally Posted By: river_rat
CATERHAM, can you post a OP vs published HTHS graph with R² correlation from Excel?


An interesting idea, but what I will provide is the raw data of some of the oils I've tested (feel free to play with the info').
All oil pressure readings were made at 6,500 rpm and oil temp' of 95C:

M1 5W-50 ..... KV100 17.5 cSt...HTHS 4.21 cP...OP 92 ...psi
M1 0W-40 ..... KV100 14.0 cSt...HTHS 3.7 .cP...OP 86 ...psi
RL 10W-30 .... KV100 11.0 cSt...HTHS 3.8 .cP...OP 87 ...psi
RL 5W-30 ..... KV100 10.6 cSt...HTHS 3.8 .cP...OP 87 ...psi
GC 0W-30 ..... KV100 12.2 cSt...HTHS 3.5 .cP...OP 83-84 psi
RL 5W-20 ..... KV100 9.1 cSt...HTHS 3.3 .cP...OP 80 ...psi
M1 5W-30 ..... KV100 11.3 cSt...HTHS 3.09 cP...OP 78 ...psi
PP 5W-30 ..... KV100 10.3 cSt...HTHS 3.1 .cP...OP 78 ...psi
RL blend, 3qts 5W-20 and 1qt 0W-10 race oil *
...............KV100 8.2cSt est HTHS 2.85 cP...OP 74 ...psi
Toyota (Nippon Oil) 0W-20 virgin, less than 30 miles on oil
...............KV100 8.8 cSt...HTHS 2.6 .cP...OP 71 ...psi
Toyota 0W-20 used with 150 miles on oil **
...........est KV100 8.0cSt est HTHS 2.4 .cP...OP 65 ...psi

* You can disregard the RL blend if you like as the KV100
spec' is calculated and the HTHS vis is an estimate only, from
RL.
** The high VI (214) Toyota oil lost oil pressure due to oil shear almost immediately in service and then stabilized which I believe must be by design as I've never seen oil shear so fast before. Consiquently I wanted to show the actual OP after just a few miles vs the virgin oil. Of course the KV100 and HTHS spec's are estimates for the used oil.

I would love to test more oils but I don't rack up much in the way of mileage so it's a long process unless I start changing out the oil at rediculously short oil change intervals.
I've corresponded with a few BITOG members who have oil pressure and oil temp' gauges in their vehicles and have encouraged them to start logging their OP readings.
Any other members with oil gauges I'd like to hear from you, so feel free to PM me.

I encourage all members to consider installing oil gauges, particularly those that have regular UOA's done. A set of oil gauges will provide a wealth of info that UOA simply can't provide and it's a one time expense unlike UOA's.


the question then becomes how many psi @ 6500rpm is enough for adequate engine protection?

is 10 psi per 1000 rpm enough?
 
Hi zoomzoom,

10psi/1000 rpm is actually a conservative mimimum OP guide if you don't know the actually spec' for your engine. In fact I've never seen a actual engine spec' quite that high.
The oil testing that I did (do) is on my Caterham (Vauxhall/Opel engine) but the minimum oil pressure spec' for my BMW is 59 psi which works out to be just over 9psi/1000 rpm. And that spec' is for maximum load (viscosity requirement) conditions. Back out of the throttle and you've just likely halved the viscosity requirements for your engine. That's one reason why it's almost impossible to run an oil too light on the street in any application.

I know you track your S4 and see oil temps in the 275-280F range.
But you're running a polymer free oil (which means zero shear)with an HTHS vis of approx' 4.2 cP. It would be nice if you had an OP gauge just for confirmation purposes but I'm sure you have more than adequate OP at those elevated oil temps'.
Of course if you had an OP gauge you could precisely fine tune your oil selection. Perhaps RL's 5W-30 alone is thick enough or RL's 0W-40 both of which would be better for street use particularly in the winter.
 
The hydrodynamic wedge is formed by the rotation of the bearings, NOT the oil pump. So, really how important is oil pressure? What you are actually measuring is the back pressure caused by the resistance of flow through the entire engine, not pressure in the bearings.

Does higher pressure really = higher flow?
 
As I've mentioned a number of times an OP gauge actually measures back pressure (resistance to flow) and is therefore a proxy for the operational viscosity of the oil in an engine; and it is the bearings that are the main contributor to the resistance to flow.

The higher the OP reading the thicker the oil and the slower the flow through the engine. Ideally speaking to maximize oil flow you don't want the oil pressure reading any higher than the design specification for the engine. But you definately don't want it lower and risk the chance of bearing wiping under high load conditions.
 
Quote:
Oil pressure is caused by the resistance of the oil to flow (viscosity) under the pumping action of the oil pump. With wide oil galleries and low viscosity oil, flow would be rapid and oil pressure low - a very desirable condition for minimizing wear. Conversely, under the same pumping conditions; with narrow oil galleries (by design or by blockage) and high viscosity oil, the oil flow will be slow & oil pressure will be high, hence resulting in less efficient lubrication.

Quote:
Influence of Viscosity
The only property of engine oil that can affect engine oil pressure is the oil’s viscosity, and oil viscosity is temperature related. However, engine oil viscosity has less effect on oil pressure when the engine is in good mechanical conditions. At normal driving speeds, there should be little difference in oil pressure between an SAE 10W 30 and SAE 20W 50 engine oil if the engine is in good mechanical condition. If engine oil pressure responds to a change in SAE grades, this is usually an indication that the engine is in need of mechanical attention.

http://www.valvolinecummins.com/Tips-Engine-Oil-Pressure.asp
 
Quote:
Highs and Lows
Low-viscosity oils flow better than high-viscosity types. The lighter-weight fluid is easier to pump and therefore circulates faster through the engine's various galleries. Low-viscosity oils also maintain a lower oil pressure, but the oil pump delivers a greater volume through the galleries than it would with thicker (higher-viscosity) oils. Heavier oils also tend to operate at higher temperatures because the oil pump has to work harder to force the lubricant through the system. Oil does not compress readily, so the added pressure increases the temperature. In the end, high-viscosity oils tend to maintain a higher oil pressure, but the pump tends to delivers a smaller volume of oil.

http://www.automedia.com/Engine_Oil/ccr20100101eo/1
 
Quote:
the question then becomes how many psi @ 6500rpm is enough for adequate engine protection?

is 10 psi per 1000 rpm enough?

This is something that I have never figured out.

Wheel bearings and cartridge bearings have zero flow and zero pressure, yet they seem to last a very long time. (Yes they are closed bearings but that is another matter.)

Now, why does oil pressure go up as engine RPM's go up? Higher volume being pushed into the same area. BUT, there must be a restriction preventing that extra oil from going some place. SO, that means there is a back log of extra oil that is not needed by the bearings causing higher pressure.

So how does this 10psi per 1000 rpm come about? It just doesn't make sense to me and we know that the oil pump does not produce the hydrodynamic film. Rotational motion of the bearing does.
 
Hi,
CATERHAM - This has been a worthwhile Thread - thanks! I would like to add a few comments that may be of interest

1 - You said this:
"and it is the bearings that are the main contributor to the resistance to flow."

Perhaps it may be more accurate to say "and it is the bearings that are one of the major contributors to the resistance to flow"

Other major contributors are the valve train and various actuators along with a few more according to engine design - but these will do here

2 - Following OP via the temperature and the OP gauges can be an imperfect science but again it will do in here

In the case of the complex V8 DOHC 48 valve Porsche 928 engine some facts may interest readers. The data below was presented to the 928 community on Rennlist several years ago. It was presented by me to try and get the message that thickest is not always better - the mandated viscosities will be shown to be better as long as the data presented is accurate. Engine driveability is directly affected!

The 928 series engines have hydraulic valve actuators and the Factory specified minimum OP is 5b @ 5000rpm with the oil at 90-100C or above (MY89 and later 5b @ 4000rpm). No idle OP is specified, the system by-pass is actuated at 8b and the oil/water intercooler is activated progressively from 87C
Typical hot OP is >1.5b at idle and >4b at 1700rpm

The following averaged data emerged from many 928 vehicles/engines and many OP readings with "hot" engine temperatures (after at least 20 mins run time and engine temp at "normal")

a - Idle OP

0W=2b, 5W=2.03b, 10W=2.42b, 15W=2.47b, 20W=2.64b
Porsche accept that 1.5b at hot is "normal" as it is in later Porsche engine families!

928 engines typically peg the gauge at 5b with cold lubricant

b - Typical OP at speed

0W & 5W-40 synthetics showed 5bar at 2300rpm (>4b at 2000)
15W-50 synthetics showed 5b at around 2000rpm
20W-50 lubricants showed 5b at/around 1700rpm
M1 15W-50 (the most popular lubricant choice) showed 3b at idle and 5b at 2000rpm

Typical on road engine speed is around 2000rpm - so it can be seen then that a SAE40 lubricant has much better flow at this speed than the heavier SAE50

Over the design life of the 928 engine family Porsche reduced the highest viscosity lubricant Approved from 20W-50 mineral to a 0W-40 synthetic

Many Owners on the advice of their "skilled mechanic" used 20w-50 or even 25W-50 mineral lubricants and typically this was "to keep up the idle OP"! Of course driveability and fuel efficiency suffered!

These engines work quite well on a 15W-50 synthetic but run and rev better on a 0W or 5W-40 lubricant. They are HTHS vis "sensitive" and require at least 3.5cP (ACEA - A3)

The "normal" operating temperature of the 928 lubricant is around 90-93C bringing the bulk lubricant viscosity to around SAE50 - as CATERHAM has alluded to

It is very difficult to persuade people that better and more linear flow is indeed better than excessive pressure
 
It appears that the correlation between HTHS and oil pressure is nearly perfect, while the correlation regarding kV @ 100C are only related as far as the fact that thicker oils tend to average higher HTHS values.
Interesting.

HTHSvsOP.jpg
 
Quote:
It should be noted that the relationship between HTHSV and engine performance have a dependency on engine design. Some of these design criteria would be oil flow rate, bearing clearances, and finish of contact surfaces which have likely changed since the correlation work of the 1980's.

http://mceinriassoc.com/id61.html
 
Originally Posted By: Tempest
Quote:
the question then becomes how many psi @ 6500rpm is enough for adequate engine protection?

is 10 psi per 1000 rpm enough?

This is something that I have never figured out.

Wheel bearings and cartridge bearings have zero flow and zero pressure, yet they seem to last a very long time. (Yes they are closed bearings but that is another matter.)

Now, why does oil pressure go up as engine RPM's go up? Higher volume being pushed into the same area. BUT, there must be a restriction preventing that extra oil from going some place. SO, that means there is a back log of extra oil that is not needed by the bearings causing higher pressure.

So how does this 10psi per 1000 rpm come about? It just doesn't make sense to me and we know that the oil pump does not produce the hydrodynamic film. Rotational motion of the bearing does.



Oil pressure doesn't increase linearly with rpm.
Depending on the oil pump, 80% of maximum pressure will be acheived at relatively low elevated rev's; say 2,500 rpm. 90% at 3,500 rpm, and something like 95% at 5,000 rpm. Maximum OP may not be acheived until 6,500 rpm or much lower with no further pressure increase as the rev's continue to rise.
 
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