HTHS

[MolaKule]

High-Temperature High-Shear is a relatively new Test and Specification.

1. What is the temperature at which HTHS is measured?
2. What is the shear rate at which it is measured?
3. Why was this spec introduced?

 

[Christopher R. Wise]

1) 302F
2) cP ?
3)????

 

[sbc350gearhead]

3)Sustained high speed operation on the autobahn?

 

[DavoNF]

1) -15C
2) Cp
3) Dunno

 

[moribundman]

1. What is the temperature at which HTHS is measured?
150 degree C

2. What is the shear rate at which it is measured?
10/second, measured in "mPas" (milli Pascal seconds, which is numerically identical with "cp" (centi Poise).

3. Why was this spec introduced?
Sufficiently high enough HTHS viscosity ensures that lubrication in bearings does not suffer under high pressure and high temperatures.

 

[jason07-1zzfe]

1) 150C
2) 1 X 10^6s^-1
3) widespread use of multi-grades?

4) QOTD for you: what exactly does #2 mean? And what are the applicational differences between all the test methods: D4624,D4683,D4741? Obviously they are with a capillary viscometer,tapered bearing, and tapered plug respectively. But, do they have different results or different application interpretations?

 

[userfriendly]

Try mechanical and sliding load capacity on hot parts such as flat tappet followers on camshafts and Diesel injectors.

 

[MolaKule]

Jason,

This is the specified shear rate at which HTHS is measured, in number of shears/second.

In other words, The oil is brought to the specified temp and then sheared at so many times per second to determine the true viscosity under these conditions.

 

[MolaKule]

Answers:

1. The temperature for an HTHS measurement is done at 150C or 302 F, which is the average peak temperature likely to be encountered in a bearing.

2. The oil is mechanically sheared at a rate of 1 x10^6 shearing operations/second.

3. Minimum Oil Film Thickness measurements (MOFT) of operating engines did not correleate well with actual wear in service. A method was devised by which the oil temperature would be elevated to worst case and sheared to determine the optimum viscosity which better correlated with wear.

Three Exxon Researchers found that a minimum HTHS of about 2.8 mPA.s was the MINIMUM HTHS viscosity needed for normal wear, with the higher the HTHS being better for minimum wear. IN general, the higher the viscosity, the greater the HTHS.

For example, in a fleet of taxicabs using a GM 4.3L V6 engine, if the HTHS was 2.35, the startup film was 0.097um and 2.56 um at running; if the HTHS was 2.98, cP, the Startup oil film thickness was 1.231 um while the running film thickness was 3.22 um.

In Dynomometer wear tests using four GM 3.8L engines, the wear mass of a connecting rod bearing was as follows:

HTHS 2.1
mass loss (gm.) - 190

HTHS 3.2
mass loss (gm.) - 28

For "mains" bearings:


HTHS 2.1
mass loss (gm.) - 150

HTHS 3.2
mass loss (gm.) - 40

A jump in HTHS by about +1.5 results in approximately 1/5 the wear. Now this relationship is not linear and flattens as one nears a 40+ weight oil.

I should also mention that this test showed little differences in wear between a high quality 5W20 and a 10W30 for oils of close HTHS. For example, The average wear of one of the 3.8L V6's showed a total wear of the Connecting Rod bearings as 48.4 grams for the 5W20 verses 44.3 grams for the 10W30. For a 10W40 oil, the wear was 39 grams!!!

[Mola's comment: I think this test verifies my earlier comments that most daily driver engines can use any oil from a high quality 5W20 to a 15W40 fleet oil.]

Summary: It was found that HTHS correlates better with wear values found in actual oil analysis and actual tear-down measurements than does measuring the oil film thickness in situ.

[ November 12, 2003, 04:50 PM: Message edited by: MolaKule ]

 

[buster]

Very interesting MK! I'd add that the UOA's have shown what you have stated in that a 5w-20 to 40wt oils are sufficient for most daily drivers.

 

[Leo]

Awesome report there Molakule.

So basically at lower temps/sheer rates, the bearing wear would be very similar across a 20-40wt oil?

And also, for a modified turbo car, a 40wt would be more ideal since the bearing load would be greater?

 

[TooSlick]

The problem with running thin oils is under high load, low rpm conditions. In this case, you don't develop sufficient oil pressure to prevent intermittant contact of the crankshaft and main/rod bearings. If you tend to lug your engine, don't use thin oils ...

Engines running at high rpms and low loads do just fine with thin oils. Hence, there are sound technical reasons why Acura/Honda can recommend 0w-20 and 5w-20 grades for the bulk of their engines.

Motorcycles are a different story, since the oil is shared between the transmission/engine - this causes significant shearing - and they run much higher oil temps ....So they stick to the 10w-40/20w-50 grades.

Tooslick

 

[MolaKule]

I think one also has to take into account that as the engine ages the clearances open up and the need for slightly higher viscosities is warranted.

I have seen this in my '92 Burb V8 engine as it crossed the 175,000 mile mark, the 5W30 oil loss was going up (about 16 oz between changes) and the 10W30's were put in place. However, at 280,000 miles, the engine does not use any oil with the 10W30 and compression is excellent with no leak down.

 

[Dr. T]

TooSlick, that wouldn't explain the BMW M3 and the Ferrari Enzo requiring a 10-60.

I think high revs and high bhp/L engines require a better HT/HS than ever before and than pushrod, high displacement engines.

 

[MolaKule]

Dr T, you bring up another question:

Why don't all automakers publish minimum HTHS's for their engine oil requirements?

 

[MolaKule]

That's the dig: Trying to weed out the specs in the specs.

Some additional Info:

http://www.tytlabs.co.jp/office/elibrary/ereview/rev324epdf/e324ab_tohyama.html

 

[TooSlick]

'Kule,

The HT/HS requirements are embedded in most of the European specifications. For example, VW 502/505 and MB 229.3 are loosely based on ACEA "A3/B4"
, so you know they require a HT/HS of at least 3.5 Cp @ 150C. The new ACEA A5/B5 calls for low vis oils with HT/HS of 2.9-3.4 Cp.

SAE/API require a HT/HS of at least 2.9 Cp for xw-30/0w-40/5w-40/10w-40 oils and 2.6 Cp for xw-20 oils ....The CI-4 rated, 10w-30/15w-40 diesel oils require a HT/HS of at least 3.5 Cp/3.7 Cp, respectively.

I'm sure you know all this stuff already ....

 

[TallPaul]

According to the 2002 API Engine Oil Classifications chart a 40 weight oil will have a high-sheer-rate viscosity (cP) @ 150C min of 2.9 for an 0w40, 5w40, and 10w40, but will have a high-sheer-rate viscosity of 3.7 for a 15w40, 20w40, and 25w40 (never heard of that one). So I am thinking that a heavier base oil is used for 15w- and 20w- oils vs the 0w-, 5w-, and 10w-. This split only occurs on in the table for the 40 weight oil. The table shows a high-sheer-rate viscosity of 2.9 also for a 30 weight oil and 3.7 also for 50 and 60 weight, but a 20 weight is listed as only 2.6, suggesting an even lighter base oil for say a 5w20 than for a 5w30. So does a 5w30 and a 10w30 have the same HTHS? I like to think that a 10w30 has a heavier base oil than a 5w30 as the low sheer-rate kinematic viscosity at 100C would suggest. I even had an oil company technician tell me that a 10w40 may have a thicker base oil than a 10w30. This would make sense to minimize the wider viscosity spread of the 10w40. Hope I am not going too far off the focus of the topic (or rambling too much), but I am trying to learn.

 

[userfriendly]

TallP...
I think you are on the right track, not to mention the pesty mono-grades which are more representive of the base oil, and shear stable.
The bearing clearance topic was discussed somewhere else on this board. The thread was called "Loose tolerance engines" or something like that.
K

 

[OilAnal]

What makes an oil with the almost equal vis#s to another have different HTHS numbers? For example, Mobil1 is less than Amsoil with both being mostly PAO content as I understand?