@edyvw
They go into further discussion of HTHS under the diagram...
View attachment 29536
QUOTE:
"The
High Temperature High Shear (HTHS) describes the
dynamic viscosity at 150°C and under the influence of high shear forces. Viscosity at high temperature and high shear rate (high speed range). Such conditions occur where mechanical components are subject to particularly rapid movements (e.g. crankshaft, cylinder track, etc.).
The
HTHS value is shown in
millipascal seconds (mPas). A higher value indicates a thicker oil film at high temperatures. This oil film would break later under these extreme conditions than those with a lower HTHS value. A higher value would therefore protect the engine more against wear, as the oil film remains permanent and guarantees lubrication. However, a lower HTHS value has the advantage that fuel savings can be achieved due to the lower internal friction and fewer exhaust gases.
HTHS limit values have also been defined in accordance with
SAE and
ACEA standards and several automotive manufacturers. They are intended to ensure that multigrade oils (e.g. 0W-30, 5w30, etc.) with VI improvers (see „viscosity index“) guarantee the necessary lubrication despite extreme temperatures and shear rates.
Such limit values are structured as follows:
ACEA A5, B5: 2,9-3,5 mPas (low HTHS)
ACEA C2: ≥ 2.9 mPas (medium HTHS)
ACEA A3, B3: 3.5 mPas (high HTHS)
Vehicle manufacturers like
VW,
Opel,
BMW,
Mercedes Benz and
Ford require a high or low HTHS value for their engines, depending on the engine type and oil approval. The HTHS value that an engine oil must have for its own vehicle is specified directly by the car manufacturer in the service manual. If an engine oil with the specification ACEA C2 is prescribed, no oil with an
ACEA A5 / B5 specification should be selected, just because it has a lower HTHS value. After all, every engine needs a certain HTHS value for its optimum performance.
For this reason, the HTHS values between the oils can only be compared if they have the same specification(s). As mentioned above, an ACEA A5/B5 engine oil would always have a lower HTHS value than an ACEA A3/B3 engine oil.
In summary, it
cannot be said whether a
high or low HTHS value is better. This answer can only be given if, for example, the specified HTHS limit values (by standards such as ACEA, API, etc.) and the temperatures and shear forces occurring are taken into account.
In simple terms, if a car drives more short distances in urban traffic, lower temperatures and shear forces occur, a lower HTHS value would be advantageous.A fast driven car during long distances would, on the other hand, benefit from a higher HTHS value.
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In short: A comparison of these measured values can only be made if the engine oils have the same specifications or approvals and are therefore subject to the same tolerance intervals.
A higher HTHS value has a positive effect on engine protection at high temperatures and high shear forces (advantageous for driving at higher speed range and long distances). A lower HTHS value has a positive effect on fuel consumption and exhaust emissions at lower temperatures and shear forces."
