HTHS vis spec trumps the Kinematic 100C vis spec'

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Originally Posted By: A_Harman
...As far as "optimum oil pressure" is concerned, the owner's manual for my Camaro states that the normal range of safe oil pressure for the LS1 engine is 20-80psi.


Generally, the oil pressure should be an incremental scale for the plain bearings protection. I hear 10 psi per 1,000 RPM for a performance engine.

20 PSI at 6,000 RPM would be trouble, 60 PSI would be great.

LS1 engines are pretty tough. It can handle a lot and even when they start knocking and the oil pressure is low, they still run forever.

Chevy engines are my favorite, particularly BBC although I have no Chevy vehicles currently.
 
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Originally Posted By: Jeff_in_VABch
Have you guys read High Temperature High Shear Oil Viscosity by James A. Spearot? I studied this about 20 years ago when it came out and have not read it lately, but I dont believe you are understanding HTHS. Also, I believe HTHS relates differently to modern engine assemblies and changes in bearing materials and crankshaft finishes in the last 15 or so years.

In the book there are also examples of where an oil with higher HTHS are capable of causing accelerated wear over one with a lower HTHS viscosity depending on the base fillers.

You can read a few pages of it here for free: http://books.google.com/books?id=XjTaOqEgHeEC&printsec=frontcover#v=onepage&q&f=false

Also, this SAE paper is a MUST read to understand current 20W events, but applies to all oil.

http://www.infineum.com/Documents/Crankc...icants-2010.pdf

Look at the tables and figures, they are great stuff. You can also see the HTHS numbers at both 100 & 150C. The bearing wear numbers look counter intuitive at first until you think about the MOFT and bearing clearances.

Combination of three things lead to metal - metal contact (oil-film breakdown) and subsequent bearing wear and failure:

(1) High torque
(2) Low RPM
(3) Low HTHS viscosity

Diesel engines have higher torques at lower RPMs and require higher HTHS viscosity in order to prevent metal - metal contact.

With gasoline engines, the engine design would dictate the load on the bearings for a given torque output, which would dictate the minimum HTHS required. One should also keep in mind that HTHS viscosity shears as well and a starting HTHS of 2.6 could easily shear to below 2.0, which would likely result in bearing failure in many engines.

Also, different driving conditions exert different loads on the bearings. High acceleration at low speeds could easily result in metal - metal contact, especially with low HTHS.
 
Originally Posted By: Gokhan
[Diesel engines have higher torques at lower RPMs and require higher HTHS viscosity in order to prevent metal - metal contact.



I dont agree on diesel engines needing more HTHS viscosity in relation to crankshaft bearings.

Diesel crankshaft bearings and oiling design is totally different from a gas engine, at least in pickup truck and HD diesels. I dont know anything about very light duty diesels, such as in a car.

Diesel engine bearings are nearly bulletproof and will nearly lubricate themselves with any petroleum liquid. It' a whole different game in a diesel oiling system.

A diesel engine, operating at a much higher compression ratio, uses the heat produced by compression to ignite the fuel. Diesel engines typically have a longer stroke than the bore diameter and to handle this load diesel crankshafts are much larger physically.

Gas engine cranks normally are cast iron and do not usually have hardened bearing surfaces. If they do have hardened surfaces they are likely to be nitrited. Heavy-duty diesel cranks are forged steel and have case hardened bearing surfaces with the most common form of hardening using the induction process. Filets on heavy-duty diesel cranks tend to be larger and the journal diameter and widths are much larger than their gas engine counterparts. That adds to the strength of the crankshaft and bearing package. The bearings are also often pinned rather than crushed to the journal.
 
In the ACEA specification you have to pass the Peugeot TU5 JP+L4 High Temperature Deposits, Ring Sticking and Oil Thickening (CEC L-88-T-02) test .

Procedure Fixture
Peugeot TU5 JP+L4 1.5-liter inline four-cylinder
engine with a modified oil sump, mounted on a
procedure stand with a dynamometer.
Procedure Parameters
The procedure runs six, 12-hour two-phase cycles,
for a total procedure duration of 72 hours. Phase 1
(11 hours 50 minutes) is at wide open throttle, 5600
rpm, 150C and 110C oil and coolant
temperatures. Phase 2 is at idle for 10 minutes.

More reading here:
http://www.swri.org/4org/d08/Abstracts/SpecLube.pdf
 
Originally Posted By: Jeff_in_VABch
I dont agree on diesel engines needing more HTHS viscosity in relation to crankshaft bearings.

They do. The minimum HTHS required by API for gasoline engines is 2.6 and for diesel engines it is 3.5.

The reason is that the minimum oil-film thickness (MOFT) inside the bearing is inversely proportional to torque and directly proportional to RPM and HTHS. Since diesel engines produce a lot of torque at low RPM, they need higher HTHS to maintain a sufficient minum oil-film thickness (MOFT) to prevent metal - metal contact (known as boundary lubrication -- with no oil film between metal parts and only antiwear additives fighting against wear).

See Page 12 and nearby pages of this link as a reference.
 
Originally Posted By: CATERHAM
...The valve train has the lowest viscosity demands in an engine, high rapid flow is what's important, particularly at start up.

Why is that?
 
Truly a great thread! I remember reading it when I first joined but was so confused at all the terminology being thrown out that I dared not respond. Now that I've been here for a while and learned A LOT about oil, kind of a blessing and a curse
48.gif
, I feel like I can ask a question.

Caterham,
You've put a ton of thought and effort into this, it is abundantly clear by this thread and your posts in other threads relating to HTHS. My question is this though:

Bob just bought himself a car and it recommends 5w30. It is his daily driver, gets up at 7 and drives 8 miles to work and drives back home the same 8 miles at 5. He'll take the occasional drive out to the lake for some fishing, once a week him and the wife go to the store, once every month or two they'll make the 2 hour drive to see the in-laws. Why on earth should he take the time to look at the HTHS values of individual 5w30 oils that meet his spec? Will a 5w30 with an HTHS of 3.1 do anything different for his engine than a 5w30 with an HTHS of 3.4? Will it affect his engine longevity? What does Bob gain by taking HTHS into consideration?
 
The valvetrain is an area of boundary/mixed lubrication, hence the need for phosphorus and other boundard lubricants.
"Dry" conditions are not uncommon and most valvetrain wear occurs on start-up and during low rpm running.
To minimize valvetrain wear over the life of an engine rapid oil flow to the camshaft is critical and in that regard the lighter the oil the better.
 
Originally Posted By: RamFan
My question is this:

Bob just bought himself a car and it recommends 5w30. It is his daily driver, gets up at 7 and drives 8 miles to work and drives back home the same 8 miles at 5. He'll take the occasional drive out to the lake for some fishing, once a week him and the wife go to the store, once every month or two they'll make the 2 hour drive to see the in-laws. Why on earth should he take the time to look at the HTHS values of individual 5w30 oils that meet his spec? Will a 5w30 with an HTHS of 3.1 do anything different for his engine than a 5w30 with an HTHS of 3.4? Will it affect his engine longevity? What does Bob gain by taking HTHS into consideration?

A good question.
Of course Bob doesn't need to know what the HTHSV is or for that matter what the KV100 is of the 5W-30 motor oil he is selecting for his car. Besides neither of the two viscosity measurements is revealed on the bottle of any brand of 5W-30 motor oil or any SAE oil grade for that matter.

As it turns out, the decision to run an oil with a HTHSV in the 3.1cP area has been made for Bob since that is what it typically for an OTC 5W-30 oil. He'd have to go out of his way to find a heavier 3.4cP oil and it would have to be synthetic and be labelled as "Euro" or "heavy duty" so it's not likely Bob is going to choose a heavier than necessary 30wt oil.

I have attempted in this thread is to assist fellow BITOGers who have already been afflicted with the motor oil bug and want to try some none specified oils or they simply want to be able to accurately compare the differences (if any) in terms of an oils viscosity as would be realized when actually used in their vehicle's engine.

The first thing most people learn about when it comes to comparing the viscosity spec's of different oils from the info they would get from a PDS, is the kinematic 100C viscosity in centistokes. Since 100C is operating temperature, it would seem to make sense that if one oil brand has a higher KV100 spec' it would therefore be thicker at operating temperature in your engine than an oil with a lower KV100 spec'.

I have pointed out that that is not necessarily the case, and if you want to make an accurate comparison you must turn to the unlikely HTHSV spec' and it is the HTHSV that is the true measure of how thick or thin an oil is at operating temperature.
And to add one further point, if both oils have the same HTHSV and the same viscosity index's, the will have identical operational viscosities at all temperatures at least as low as
0C.
 
Originally Posted By: RamFan

Bob just bought himself a car and it recommends 5w30. It is his daily driver, gets up at 7 and drives 8 miles to work and drives back home the same 8 miles at 5. He'll take the occasional drive out to the lake for some fishing, once a week him and the wife go to the store, once every month or two they'll make the 2 hour drive to see the in-laws. Why on earth should he take the time to look at the HTHS values of individual 5w30 oils that meet his spec? Will a 5w30 with an HTHS of 3.1 do anything different for his engine than a 5w30 with an HTHS of 3.4? Will it affect his engine longevity? What does Bob gain by taking HTHS into consideration?


We don't deal with just average Bob guys here. We deal with Bob Is The Oil Guys...
lol.gif


The fact is probably 95% of the stuff discussed here won't matter a hill of beans to the average engines life. The fact that we are says to me that we already care more than the average person so we talk about things that the average person doesn't.

I think Caterham's post regarding the valvetrain at least partially answers your question. Will 3.1 vs 3.4 affect Bob's engine longeviy...probably not. Could 3.1 get Bob closer the the "ideal" lubricant for his engine and opperating conditions, providing the best mix of protection and efficiency? Possibly.
 
Caterham,

Okay, I'll confess up-front that I read your first post very carefully but promptly skipped to the last page to ask my question.

Are viscosity-improved oils technically shear-thinning fluids? If you search this term on Wikipedia you'll see what I mean.

Water, for instance, is not shear-sensitive. It has the same viscosity regardless of how much shear stress it is experiencing. Of course its viscosity will change with temperature. I suppose we also need to get our textbooks out and remind ourselves what the definition of viscosity is. I come from the polymer industry, and polymers are highly shear-sensitive materials. If molten polymer is being pushed quickly through a channel or the channel is small, then it experiences a high shear stress and will thin out. Injection molding processes often have shear rates in the neighborhood of 10,000 reciprocal seconds or more, causing some polymers, like nylon, to drop in viscosity by a factor of 10 or more. There are also shear-thickening "fluids," such as wet sand.

I was always under the impression that oil was an ideal, or non shear-sensitive, fluid. If it isn't, then it makes perfect sense to me that more sophisticated instruments (HTHS) would be necessary to simulate its response at service temperature AND under service pressure/shear. Plus, dropping a ball through a column of oil may be a repeatable measurement but it's certainly not as precise as a rheometer which can actually put the oil under a constant shear stress (such as a parallel-plate rheometer).

Now I think I need to read up on how hydrodynamic lubrication works!!
 
The question is: Are viscosity-improved oils technically shear-thinning fluids?

The answer is yes, but to differing degrees, depending on the type and amount of Viscosity Improver used. The origin of the HTHS test is related directly to this. In the 1960's it was found that despite high viscosities that were measured in falling-ball kinematic viscometers, some multi-viscosity oils with high VII content were not protecting engine bearings as well as straight-weight oils of the same high-temperature rating. So the HTHS test was developed in which the test oil is heated to 150C and subjected to a shear rate of 1,000,000 reciprocal seconds (surface velocity divided by oil film thickness). It was indeed found that multi-grade oils lost a higher percentage of their viscosity than mono-grades when subjected to higher shear rates than in the falling-ball test.

In general, if you could extrapolate the KV100 spec to 150C, and convert to dynamic viscosity, you would find that the ratio of HTHS to the dynamic viscosity at 150C decreases as the viscosity spread increases. I have done this for the various grades of Redline oils, and the 40-weight data is interesting:

Grade, HTHS/DV150
0w40 = .752
5w40 = .909
10w40 = .967
15w40 = .987

for Redline's 50-weights:
Grade, HTHS/DV150
5w50 = .875
15w50 = .935
20w50 = .995

So in general, the wider the viscosity spread, the more viscosity loss there will be due to temporary shear as an oil passes between moving surfaces.
 
Originally Posted By: A_Harman

So in general, the wider the viscosity spread, the more viscosity loss there will be due to temporary shear as an oil passes between moving surfaces.

Except the HTHSV spec' already takes temporary shear into account so one doesn't have to be concerned about it.
One should choose an oil based first on it's HTHS viscosity and secondarily on it's 0W, 5W etc rating and viscosity index.
And while a high VI is always better, how it is acheived; i.e., the amount of polymer thickeners used and their quality, should be taken into account to access permanent shear stability.
 
Originally Posted By: CATERHAM
Originally Posted By: A_Harman

So in general, the wider the viscosity spread, the more viscosity loss there will be due to temporary shear as an oil passes between moving surfaces.

Except the HTHSV spec' already takes temporary shear into account so one doesn't have to be concerned about it.


Yes, it's still the HTHS spec that tells how well an oil will protect in extreme conditions. But I do wonder how well HTHS holds up after an oil has 3000+ miles. I think that lower viscosity spread would be better, but don't have any data on aged HTHS to look at.
 
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HTHSV is an accurate measure of how thick or thin an oil is in an operating IC engine. The fact that it is measured at 150C (it is also measured occational at 100C) throws some people as being some sort of extreme measure only but it shouldn't.
Viscosity change with temperature is virtually linear from 150C down to 100C and even lower to 80C with lighter 20wt and 30wt oils. That's an additional reason why one can totally ignore the KV100 spec' in comparing the expected operational viscosity of different oils at normal operating temp's.

Asking "how well HTHS [viscosity] holds up" in service is the wrong question. HTHS is simply a measure of viscosity which has nothing to do with oil shear. Having said that, what's cool about HTHSV is that is correlates with oil pressure, so if you notice a drop in OP as the miles rack up you know you've got a loss of viscosity which is due to either oil shear and/or fuel dilution, Either way it would be a reduction in the HTHSV of the oil.

Additionally, I really don't like the laymans phrase "viscosity spread" as derived from the SAE oil grade. It's not part of a tribologist's vernacular as the temperature variation is too extreme. An oil's viscosity index has much more relevance in the discussion of oil shear and as a predictor of what can be expected; i.e., high VI finished oils tend to shear more than low VI finished oils. Again whether that holds true has everything to do with the natural VI of the base oils used and the amount and quality of the VIIs that may contain.
 
Supposing we have two oils, with the same value and the same HTHS value and same VI, but with different grade, example:
5w30 with VI 170 and HTHS 3.6
5w40 with VI 170 and HTHS 3.6

Ambient temperature is the same (68°F).
The action of the two oils will be the same?
What changes is the flow of the pressure?
 
Hi Vincenzo,

Yes the two oils will have the same viscosity characteristics with the same oil pressure gauge readings and he same pressurized oil flow rates through an operating engine at all temp's down to at least 0C.
Since the 40wt oil will have a higher KV100 that could be an indication of more VIIs are being used in it's formulation and therefore it may be more shear prone in service.
 
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