Sorry, I might not have been clear there: I'm talking about the film thickness. The film thickness, under a given load and relative sliding speed goes UP as viscosity gets higher/oil temp gets cooler.
That's a basic hydrodynamic law, the film strength is a bit more complex, I think. Oils can have additives that wil make a film "stronger" ie less prone to rupture under load spikes/extreme pressure etc, and that's when you get into the magical mystical additives that the OE suppliers are so protective about.

But in purely hydrodynamic terms, if an oil's thicker, it's going to take more load to break the film. Nothing to do with how "good" the oil is, just how thick it is. Once the film's broken and you get metal-to-metal contact it's not a fair comparison.
The reported test is actually pretty harsh, since there are few areas of the engine where you actually see such loading - almost point contact, and sliding, rather than rolling contact.

 

Oil film strength is primarily determined by an oils additive package, that's why you see such a wide variation in film strength between different brands of oil, even with the same viscosity. Royal Purple's proprietary "Synerlec" extreme pressure additive, is likely the best on the market.

The oil wedge action that many of us think of regarding rod, mains, and cam bearings, takes place mostly in those areas. That is, areas where you a round shaft spinning in a concentric bearing with a reasonable clearance for oil to form that wedge to keep the parts seperated. And you only have that, once oil pressure is established, you DON'T have it on start-up. During start-up and in most other areas of the engine, you see oil shearing action (as was done in the test), not the wedge action. That's why the test WAS VALID for our engines.

Anyway, here is a summary of the test:

1. ROYAL PURPLE Racing Oil full syn 20W50 withstands 295,722 psi

2. ROYAL PURPLE Street Oil full syn 10W40 withstands 131,432psi

3.VALVOLINE DURABLEND semi-syn 10W40 withstands 23,858psi

4. PENNZOIL semi-syn 10W40 withstands 9,200psi

5/6. Tie RED LINE full syn 5W40 withstands 6,389psi

5/6. Tie MOBIL semi-syn 10W40 withstands 6,389psi

7. SHELL semi-syn 15W50 withstands 2,920psi

8. SHELL full syn 5W40 withstands 2,567psi

9. CASTROL full syn 0W40 withstands 2,011psi

10. MOBIL 1 full syn 0W40 withstands 1,540psi


Oil film strength is what protects an engine from wear and/or failure by preventing metal to metal contact.

You can see that cold viscosity alone didn’t really factor in all that much, because #2 was 10W40, while #7 was 15W50. You can also see that full syn vs semi-syn didn’t factor in much, because #1 and #10 were both full syn. So, looking at this chart, you just have to decide what you are willing to live with.

 

Yes, no doubt individual maker's additives are responsible for some of the load carrying variation within a viscosity grade. Looks like the Royal Purple does appear to be doing something right, additive wise.


Don't forget that these grade numbers ARE NOT direct measurements of viscosity, but "brackets", and two oils of the same grade can and do have measurably different viscosities. So this goes a little way to explaining the load bearing differences between the apparently similar graded oils.
But look at that list - the two poorest performers are the the 0W's, the best is the "thickest", 20W50! There's a bit of cross over in the middle but I stick by my original point that we're looking at results that are clouded by the effect of viscosity.

A "proper" wear test must have a TIME dimension, ie how much material is removed in a given time. There's no mention of how long the wheel and bearing were allowed to run against each other after the film ruptured, and I wonder if it was even controlled. Using the wear scar length in that equation is misguided for that reason. I wish there was an explanation of what that equation was based on, they just seem to state it as a given. Of course the wear scar is going to be longer, if the oil's film ruptured at a higher loading. Something's not right there for a start.

With regard to startup, in fact, it's a bit of a misnomer that you NEED oil pressure (ie from the pump) to keep a journal bearing happy - in fact it builds it's OWN pressurised film with just a tiny amount of residual oil, when you think about the amount of oil needed to fully flood the clearance space in a journal bearing, it ain't much! Provided there's some residual oil around from the last run, the bearing should build up a wedge pretty quickly at startup (there's always going to be some contact tho..)
The purpose of the pump's pressurised oil flow is more to flush the heat out of the bearing, and to make sure there's always much more oil available than demanded.

The pressure in the bearing and the pressure of oil being fed to it are not directly coupled. The pressure in the bearing is a function of the rotation speed, the oil temp/viscosity, the clearance and the eccentricity and in a well flooded bearing is many times higher than the 30-40 psi that the pump's providing. It has to be to support the tons of load that get hammered down the con-rod.

Think if it this way; you could never support a conrod load (which could reach 1000s of lbs) on the pressure from the pump of 40odd psi. The pressure inside the bearing is many times higher, and largely unrelated to the feed pressure.

 

Went away and got to thinking (dangerous!) - found this on Wikipedia, which suggests this Timken OK load test is not only outdated, but not actually intended for these types of lubricants, and also designed against the current thinking.

http://en.wikipedia.org/wiki/Timken_OK_Load

Note the test is intended for EP lubes, and all the oils here fell well under the EP load measure of 35lbsforce.

I must admit that although I wasn't all that comfortable with the results before reading this, I was willing to give them some credit just for taking the time to do a test. But I think this wiki article makes the results seem even more "curious". Did Royal Purple fund this experiment!?

Full text:



Timken OK Load
From Wikipedia, the free encyclopedia
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Timken OK Load is a qualitative measure that indicates the possible performance of extreme pressure additives (EP Additives) in a lubricating grease or oil. The units of measure are pounds-force or kilograms-force and are determined using a special test machine.

The test machine is based on a machine manufactured by the Timken Company from 1935 to 1972. It is now an industry standard test though the meaning of the qualitative measure has become less useful as the science of tribology has advanced.

The test machine consists of a bearing race mounted on a tapered arbor rotating at high speed. The race is brought into contact with a square steel test block under load. The contact area is flooded with the lubricant being tested. The Timken OK Load is the load at which the spinning bearing race produces a score mark on the test block.

Though Timken no longer manufactures the test machine, Timken OK Loads are still listed on grease and oil property charts. It was once generally assumed that the measure and the film strength of the lubricant were directly related. Today, the primary purpose of the test is to determine whether EP additives are present and functioning. A measure of 35 pounds-force (16 kilograms-force or 155 newtons) or more means that EP additives are present and working.

The Timken OK Load test specification is ASTM 2509.

 

I've seen this test before and like theoUK, I was skeptical of the results, but clearly he his much more knowledgeable than I am in this area. Appreciate the insights you have shared with us!

For a more comprehensive oil test that many of you might find interesting, AMSOIL included Royal Purple in this test of motorcycle oils. The results are somewhat contradictory to the article posted at the top of this thread.
AMSOIL Motorcycle Oil “White Paper” (1 MB pdf file)

 

Subdriver

Thanks. As for my insights, cheers for listening to my ramblings

Thanks for attaching the AMSOIL test data, I've had quick scan through it, will save it for later. Interestingly, I went straight to the wear test page (#13) and noticed that a Mobil 1 test oil performed around the best, with a royal purple oil coming in last! Totally on its head, compared to the first test. As you guys across the pond say, Go figure. Also note that their wear test is carried out for a FIXED time period, speed and load on each oil. Ie the way I think it should be done

It just goes to show that sometimes there's as many outcomes as there are tests. You have to be pretty careful what you believe. As far as we know, both of these tests could be great, or both could be a load of old BS.

You might be interested to know that we're doing fuel economy and friction tests for a major Oil supplier at the moment, on a batch of nominally similar oils, each with different additive packages. Trying to rank them in order of economy/friction benefit. We're working along side another group who are also testing the same oils, but in a slightly different way. In terms of results, our tests, their tests, and the Oil supplier's "industry standard" test each conclude with the oils in DIFFERENT rankings! So who do you believe?! It really is quite a complicated problem. At least in our tests, I'm not the one who's actually selling the oil! So hopefully pretty impartial!

Anyway, thanks Subdriver and 540RAT for providing some good food for thought! The debate, and dead-horse-flogging, will no doubt rage on

Theo

 

Each to his own, but if you want max protection for real high performance/race engines, the extra Royal Purple film strength starts to look real good. As I said earlier, big blocks tend to lose roller lifters, and the extra film strength may be what is needed to make them live. Royal Purple's early products were developed for similar problems with industrial machinery, which it cured.

Plenty of hardcore dragracers use 0W? Royal Purple racing oil, which is of course very thin, so they barely hold any oil pressure. They do it for max hp that the thin oil helps with, yet the internals look like new when taken apart.

Racing Engine builder Joe Sherman got an extra 30hp in a 600hp small block Chevy just by switching from Valvoline 20W50 dino racing oil to Royal Purple 5W30 racing oil. He never saw that in any other oil. He uses it all the time in his shop and has nothing but good things to say about it. The best film strength and more hp, I'd say that was rather impressive myself.

Their street oil meets recent API requirements as well as GM's own GM4718M oil requirement for Corvette's, GTO's and others. So it must be pretty good on that count as well, because not all oil meets that requirement.

I have been using Royal Purple 5W30 street oil in two of my late model cars for some time now without issue. One is just a 200hp V6 daily driver, and the other is a 550hp supercharged V8 muscle car. They have been just fine, and in fact the supercharged engine's idle went up 100 rpm. A few other people I know, have been using it as well, and also like it just fine.

So the question I have for you naysayers is, what oil do you use in your own engines? And if the tech specs on an oil is not how you decide which oil to run, just how did you decide on that particular oil? About all that is left is guesswork and marketing hype, right?

 

Just curious.... Did you buy 20W50 oil in your "favorite" brand, as well? Or just with the Royal Purple. More viscous oil has better film strength. If your "old" brand was 10W30, the test won't mean anything. That's not to say that Royal Purple isn't a very good oil...I'm just saying that a bad test is just that....a bad test. You can't learn anything from it. If the variables in the test were the same, I would go along with your conclusions.

 

540rat..

As I said before, that magazine test definitely showed the Royal Purple stuff to be capable of holding higher load before film rupture. Whether or not their testing method was flawed, that does definitely say something good about that oil. I don't doubt the quality of the stuff, my only problem was with the way they undertook their testing.

Personally, I'm not "naysaying" with respect to the Royal Purple oil, only the test method (see above!)

As for oils which I use, I drive two cars, a 20-year old 140,000mile VW Golf, and the 90,000 mile vette. With the Golf, the sheer age and lack of value of the thing just doesn't warrant spending too much on synthetics, so I go for a mineral variety from my local VW aftermarket specialist (not dealer) which meets the VW specs laid down for this car. (I forget which numbers the specs are). Its a 20W40, because I want to keep some oil pressure in this old engine.

As for the vette, again I don't go crazy, because this engine's due for a rebuild some time soon. I stick with a "decent" Castrol 20W40 mineral. Once that engine's been rebuilt, I'd start to look carefully into a good synthetic to use, but until that time it's really a waste of money throwing expensive stuff at it. I've rebuilt all the other "oil-using" bits of the vette, diff, p/s pump, autobox and after that I've stuck with GM fluids.

If i'd invested much time and money in either of my engines, I'd want to use some decent stuff. But even then it's hard to decide, as so often all you have to go on is the hype. That's why tests like those shown here are so welcome...... but only when they've been carried out with some decent scientific rigour!

 

How would YOU do it, so that it would be scientific enough for you?

 

Well there's the problem. There's no denying that, as I said above, it's very hard to know.

To be totally honest, to make it scientific enough, I'd want some good laboratory wear testing to be done. But of course that's not exactly something we can just knock off in the garage. When it came to the crunch, if I was really seriously contemplating what would be a good oil, then I'd be searching through as many technical papers as I could, preferably from independent (ie not affiliated with brand "x" or "y") researchers, so probably SAE publications (or our UK equivalent, the IMechE) However, even then you'll often only find that a particular additive is good for wear, rather than a particular brand. And with the oil co's being so cagey about their magic ingredients it's hard to buy an actual oil based on the choice of what's in it, 'cos you might never be able to find out!


Decent research information is available, but at a cost. You can download pretty much any paper you want from SAE (again for price). (I have the slight advantage of being in the industry and can access some of this information slightly more easily). And a good chunk of it doesn't require you to be a lubrication expert to understand it.

For the regular petrolhead, I think the only "solid" thing you have to go on is the specs that a certain oil is advertised to meet or exceed, ie the OEM-type spec. You have to hope these tests are pretty rigourous and carried out in a controlled way. Everything else is, by its very nature, either hearsay or marketing hype.

That's probably part of the problem, why defining a "good" oil is so difficult, since there's very little quantifiable information out there.
You can say a particular cam or heads makes good power by measuring it on the dyno, it's not like you can make a similar measurement of the "goodness" of an oil, other than perhaps the reduction in friction it gives you (but that still doesn't tell you how it will look after your rockers after 100,000 miles!)


I'm sorry not to be able to give a more definitive answer, but there just isn't one.
So given the lack of information, tests like that magazine one have the potential to be really useful, and I'm sure that particular one was carried out in good faith, but we've already been over my feelings about certain bits of it.
I should add that I DON'T think the test showed Royal Purple to be unfairly better than it is, kind of the other way round: I think the performance of the OTHER oils is cast in a disproportionately POOR light by showing those big wear scars. That was not a proper wear test.

I've not had a proper look at the other paper that was posted, need a spare ten minutes to digest it....

 

Um, Ok.

There's nothing logical about the choice to own a C3 vette (specially not in this country when juice is about ten USD a gallon!), it's pretty much as you describe it, a total "heart-before-head" decision. I knew next to F-all about them and mine was only the second one I'd ever seen "in the flesh". Despite all my ramblings above about making informed decisions, I'm still basically a big kid at heart and think these cars about the coolest things on the planet

I've had her since I was 22, with no regrets, and despite all the ****ling little issues there's not much better than whipping the top off and going for a blast.

As for the Golf... Jeez, that thing cost me 200 quid at a point when I needed some cheapo day to day transport and I never look at it as a good investment! It's going to be run into the ground. But given that it's virtually indestructable and, it think, carved out of a solid billet of German Qualitat, I always get the impression it will live forever! I looks like a turd tho. And handles like one. And accelerates a little bit slower than one. Imagine, red-brown paint with a brown-on-brown interior. Niiice. Although oddly I'm quite fond of her too...

 

I use have been using Mobil 1 since I rebuilt my big block, and it has given me no problems through all my track days, sitting all winter, street driving, etc. What made me choose Mobil 1? I had an old Suzuki 500cc motorcycle when I was in high school. During a ride in the desert, the drain plug came out and all the oil with it. I had no idea until the engine siezed up. My dad went back to camp, brought back some more Mobil 1 and a spark plug to replace the drain plug (same thread) and the engine started right up. I rode the bike for another couple of years before selling it to my cousin. He road it for some more years, and the engine never had a problem.

I use a Castrol synthetic for my VW diesel because it meets the VW spec. If they catch you using oil that doesn't meet the spec, your warranty is void. It's expensive and hard to find, but the oil only has to be changed every 10,000 miles.

I use the stock Valvoline Blue oil for my Dodge diesel because it's what Cummins uses from the factory. I know what kind of testing goes into the truck and engine, so I use the same oil Cummins/Dodge use. It gets changed every 3000 miles because of the driving I do.

I think the test can be used as a reference point, but so much goes on in the engine that the test doesn't measure. For one thing, what happens to the oil when it's been sitting in the car through huge temp changes overnight, or for a few weeks? How does the resulting condensation affect the oil's lubricating ability?

Like many, I think you need to try some oils and then actually look inside the engine. That can be tough for a second/fun car, so at some point you need to make a decision and live with it.

Ken