HTHS vis spec trumps the Kinematic 100C vis spec'

[Shannow]

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.


Yep, the bearing doesn't need ANY pressure to operate as a hydrodynamically lubricated bearing. I've seen big bearings actually operate under suction on the oil feed in side, where the low pressure side of the bearing sucks on the supply control orifice.

The pressure is the mechanism through which sufficient oil to replenish and cool the bearing is supplied to the bearing.

The 10 psi per 1,000 Revs is an old Small Block race rule of thumb to ensure that there is sufficient oil volume to keep the bearing fed at the most remote drilling of the oil galleries, when the pressure set point is controlled at the oil feed in point.

If pressure were controlled at the worst bearing, then the recommendation would be a fraction of that.

 

[Tempest]

Originally Posted By: CATERHAM

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.

Thanks for the info. Unfortunately, none of the cars I drive have an OP gauge to test all of this with.

What you state here makes perfect sense, though. As the pressure increases it will eventually trip the relief valve and you won't get any higher. It wouldn't surprise me if the valve is open a little even before one gets to max pressure.

 

[Tempest]

Quote:
I've seen big bearings actually operate under suction on the oil feed in side, where the low pressure side of the bearing sucks on the supply control orifice.


I service an evap. cooler and these have plain bronze bearings on the fan with an oil reservoir around them. This unit is about 6 years old with the original bearings and it hardly uses any oil (a few drop a year). The RPM's are fairly low. This is one reason why all of this oil pressure talk around the forums is perplexing.

Pushing a bunch more oil than is required for AW in order to provide cooling also makes perfect sense.

 

[river_rat]

Originally Posted By: CATERHAM
Oil pressure doesn't increase linearly with rpm.

Mine does. Or nearly so, until the relief starts opening at 85-90 psi. That only happens at lower than full temp.
Then I get almost exactly 17.2 psi/1000 rpm between 1000 and 5000 rpm on my Tacoma 4 cylinder truck with 5W-30 at full temperature.

 

[river_rat]

I should add this is with Amsoil ASL: HTHS 3.2...and yes the gauge is quite accurate across this^^^ entire range, as I checked calibration just before its recent installation.

 

[CATERHAM]

Hi Doug,

Well I don't know if other BITOG members appreciated the detailed info' on the lubrication of the Porsche engine but I sure do since I have one! Thanks a lot.

I didn't know the 928's oil pump's pressure relief setting was as high as 8 bar (116 psi). It's the same as for a freinds Acura NSX which has a higher rev limit of 8,000 rpm to the 928's. Lighter oil is specified as well, a 3.1 cP 5W-30 and the minimum "test" OP spec's are lower at 10 psi for idle and 50 psi (3.4 bar) at 3,000 rpm.
And it's nice that the factory OP gauge is not pegged (unlike the Porsche) so you will see 8 bar on the gauge if you rev the engine cold. It's a good self imposed check to encourage short shifting until you get some heat into the oil.
I wish Porsche didn't peg the gauge at 5 bar, which I believe they still do on the newer models as it really limits the gauge's usefulness.

You said; "Following OP via the temperature and OP gauges can be an imperfect science".
It can if the factory gauges are inacurate or incomplete, consiquently one must often install accurate aftermarket gauges. But if you're an oil nerd like I am it's well worth the effort.

What is imprecise is comparing different oils based on their SAE grade alone. There is just too much variation within an SAE grade or even between two grades in some cases. I mean who would have thought a 5W-20 was heavier than most 5W-30's, but that's the case with RL's POE based, VII free 5W-20. In fact that's the case with most ester based oil's, they punch above their weight so to speak

 

[CATERHAM]

river_rat, thanks for the great graphs.

I think you've summed it up well when you said;

"the correlation between HTHS and OP is nearly perfect, while the correlation regarding Kv @ 100C are only related as far as the fact that thicker oils tend to have higher HTHS values."

 

[21Rouge]

Originally Posted By: CATERHAM
"the correlation between HTHS and OP is nearly perfect, while the correlation regarding Kv @ 100C are only related as far as the fact that thicker oils tend to have higher HTHS values."


So with this statement maybe we are seeing the beginning of a shift away from the importance of the Kv # at 100C?

 

[mechtech2]

Concerning lubrication, ball bearings are way different in their needs than a plain bearing . They require very little.
Bronze oilite bearings are self lubricating, and are used for different purposes/loadings than a car engine's plain bearings.

 

[Doug Hillary]

Hi,
CATERHAM - Thanks for the comments. I have long pushed the importance of using at least the OEM's minimum mandated HTHS viscosity when using non Approved lubricants. It is of course a cornerstone of the ACEA's system - ACEA is an amagam of the vehicle/engine manufacturers - unlike the API! The API only moved to the minimum HTHS requirement in the 1970-80s via the US diesel engine manufacturers which mandated a 3.7cP rating for their Approved HDEOs (probably driven by CAT)

The 928's engine will remain in lubrication system bypass for well over 5 minutes when using M1 15W-50 (a lubricant with excellent flow properties) from a cold start (dyno results)

The 928 "project" was done to allow Owners to understand why a 2b reading at hot idle was better than the 5b that had been idicated to them by their independent expert Porsche mechanic(s)! This was common in the US and elsewhere. I first became aware of this widespread misinformation in the Snowy Mountains here in OZ during a Rally. At least one 928S4 Owner had been using 25W-50 mineral lubricant on the advice from his independent servicing expert! His OP gauge never left the 5b mark. This meant that the lubrication system was in by pass from around 1200rpm and the flow rates through the ring pack and valve gear was very slow indeed - increasing the risk of higher localised wear rates and the chance of unwanted deposits

The 928 project also involved many UOAs and IR temeprature readings

The only reason I use the 5W-40 lubricant I do in my M96 Porsche engine is its superior HTHS viscosity. My M96 runs hotter than most due to some intentional modifications. This is not needed in the Benz engine

Correct flow at temperatures below 60C or so is extremely important in many of the more complex engines produced today

 

[river_rat]

Originally Posted By: CATERHAM
river_rat, thanks for the great graphs.

I think you've summed it up well when you said;

"the correlation between HTHS and OP is nearly perfect, while the correlation regarding Kv @ 100C are only related as far as the fact that thicker oils tend to have higher HTHS values."


Sorry about having to kind of squint to see the numbers.
The correlation for the HTHS graph reads 0.994 and 0.7312 for the KV graph.
Basically then, the HTHS value gives a 99.4% accurate predition of the expected oil pressure in this engine, in this test, vs 73.12%.

 

[Y_K]

Thank you, gentlemen for the meaningful thread and excellent illustrations of your take on the matrix.

 

[CATERHAM]

Originally Posted By: 21Rouge
Originally Posted By: CATERHAM
"the correlation between HTHS and OP is nearly perfect, while the correlation regarding Kv @ 100C are only related as far as the fact that thicker oils tend to have higher HTHS values."


So with this statement maybe we are seeing the beginning of a shift away from the importance of the Kv # at 100C?


I fear only among the motor oil cognoscenti.

A solution is to do away with the kinematic method of measuring and reporting an oil's viscosity but that won't happen unless someone finds an inexpensive way to incorporate shear and pressure into the 100C vis' spec', the same methodology that's done for the HTHS spec'.

 

[21Rouge]

Originally Posted By: river_rat
"the correlation between HTHS and OP is nearly perfect, while the correlation regarding Kv @ 100C are only related as far as the fact that thicker oils tend to have higher HTHS values."


Originally Posted By: 21Rouge
So with this statement maybe we are seeing the beginning of a shift away from the importance of the Kv # at 100C?


Originally Posted By: CATERHAM
I fear only among the motor oil cognoscenti.


CATERHAM I would be willing to bet that the term cognoscenti has never been used in conjunction with the phrase "motor oil"!

 

[river_rat]

I love that word. It makes me feel like we should be wearing dark sunglasses and going to party where the bouncer only lets you in if you are "on the list."

 

[zoomzoom]

Originally Posted By: Doug Hillary
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


great info Doug!

now what I would like to know is what happens when you are tracking your car and oil temperature are in 250-280F range..would 40wt still be fine?

 

[Doug Hillary]

Hi,
zoomzoom – As you know the purpose of the Thread was to establish where HS viscosity sits in relationship to Kinematic viscosity at 100C. Establishing some relationship to OP was also sought

In answer to your question, IME a lubricant that meets at least the minimum HTHS viscosity would be the winner as long as the minimum allowed OP is maintained – and some SAE40 lubricants of course share the same minimum HTHS viscosity as the SAE50 grade. In this case the SAE40 lubricant is likely to have the best flow characteristics over a wide temperature range which aids cooling. Porsche 928 engines that have failed when racing have almost invariably suffered from oil starvation (no dry sump) during high cornering forces! The viscosity mattered very little – at the margins a higher HTHS viscosity synthetic lubricant may have prolonged life a little!!

Whilst I can’t provide you any more details, a number of BMWs used 0W-20 synthetic lubricants supplied by Castrol and FUCHS during the recent ADAC 24hr event at the Nurburgring

The Porsche Museum in Zuffenhausen uses 15W-40 and 20W-50 mineral lubricants in its older engines. These are warmed to 80C before any serious activity occurs! Of course M1 0W-40 is used in its modern race cars

The Porsche 928 engine had some lubrication system modifications during its long production life. These included changes to engine castings and seals to prevention sucking air, a larger oil pump to assist oil pressure at hot idle and the repositioning of the oil cooler and at the same time changing it from a oil to water intercooler to an oil to air version. During this time the preferred oil viscosity changed from a 20W-50 (max viscosity-mineral) to a 10W-30 synthetic until finally settling on a 5W-40 synthetic. The minimum HTHS viscosity was 3.5cP and no SAE30 lubricant was Approved for this engine after 1999

Of course Porsche’s Approval process includes extended viscosity test periods at 100C and 150C (to ACEA’s criteria) with a minimum Kinematic viscosity of 11.3Cst at 100C

Ultimately, much depends on the lubricant’s structure and its abilities/durability against temporary and permanent shear test criteria! IMO using at least the minimum HTHS viscosity mandated by the engine manufacturer should always be a prime consideration in any lubricant choice

 

[AMRoberts]

Trying to get my brain wrapped around this thread ...

Originally Posted By: Doug Hillary
... I have long pushed the importance of using at least the OEM's minimum mandated HTHS viscosity when using non Approved lubricants. It is of course a cornerstone of the ACEA's system

So if I look at the Mobil 1 High Mileage oils, the reason (or at least one reason) why the 5W-30 isn't rated as ACEA A3/B3 or A3/B4 is HTHS viscosity < 3.5, correct?

Thus even though the viscosity chart in the 2007 MB MB Factory Approved Service Products document that Oldwolf posted shows 5W-30 as acceptable across a wide temperature range, this particular 5W-30 would be a less-than-ideal choice for my 1995 E320, given that the document specifies A3/B3 for 1997 and earlier?

Originally Posted By: Doug Hillary
...The only reason I use the 5W-40 lubricant I do in my M96 Porsche engine is its superior HTHS viscosity. My M96 runs hotter than most due to some intentional modifications. This is not needed in the Benz engine

Mobil's PDS for the 0W-40 lists HTHS viscosity as 3.7. I couldn't find a specification for the Delvac 1 ... Is it substantially higher?

 

[BobFout]

Originally Posted By: AMRoberts
Trying to get my brain wrapped around this thread ...

Originally Posted By: Doug Hillary
... I have long pushed the importance of using at least the OEM's minimum mandated HTHS viscosity when using non Approved lubricants. It is of course a cornerstone of the ACEA's system

So if I look at the Mobil 1 High Mileage oils, the reason (or at least one reason) why the 5W-30 isn't rated as ACEA A3/B3 or A3/B4 is HTHS viscosity < 3.5, correct?

Thus even though the viscosity chart in the 2007 MB MB Factory Approved Service Products document that Oldwolf posted shows 5W-30 as acceptable across a wide temperature range, this particular 5W-30 would be a less-than-ideal choice for my 1995 E320, given that the document specifies A3/B3 for 1997 and earlier?

Originally Posted By: Doug Hillary
...The only reason I use the 5W-40 lubricant I do in my M96 Porsche engine is its superior HTHS viscosity. My M96 runs hotter than most due to some intentional modifications. This is not needed in the Benz engine

Mobil's PDS for the 0W-40 lists HTHS viscosity as 3.7. I couldn't find a specification for the Delvac 1 ... Is it substantially higher?


TDT's HTHS is 3.9, I would not expect D1, or D1 ESP, to be too much different.

 

[CATERHAM]

Originally Posted By: CATERHAM
Originally Posted By: 21Rouge
Originally Posted By: CATERHAM
"the correlation between HTHS and OP is nearly perfect, while the correlation regarding Kv @ 100C are only related as far as the fact that thicker oils tend to have higher HTHS values."


So with this statement maybe we are seeing the beginning of a shift away from the importance of the Kv # at 100C?


I fear only among the motor oil cognoscenti.

A solution is to do away with the kinematic method of measuring and reporting an oil's viscosity but that won't happen unless someone finds an inexpensive way to incorporate shear and pressure into the 100C vis' spec', the same methodology that's done for the HTHS spec'.


Actually James Spearot suggested doing away with the kinematic
measure 20 years ago (see material starting on page 44 from his paper "Spearot on Relating HTHS Viscosity to Engine Operation":

http://books.google.com/books?id=Fu-99Mc...p;q&f=false

"the development and widespread use of viscosity index (VI) improver additives has rendered kinematic viscosities technically obsolete; their primary use today being that of a tool for marketing engine oils"