Key Takeaways
- HTHS is a performance metric, not a general description of oil thickness.
- It is especially important in highly loaded engine contacts.
- Two oils with similar VI can still differ meaningfully in HTHS viscosity.
Definition
HTHS viscosity stands for High-Temperature High-Shear viscosity. It describes how a lubricant behaves under elevated temperature and severe shear conditions that are closer to real loaded contacts than ordinary kinematic viscosity measurements.
This metric is especially important in engine lubrication because it helps indicate the lubricant film’s ability to maintain separation in areas such as bearings and valve train contacts. It is typically discussed in units of mPa·s and is commonly referenced alongside engine-oil specifications.
Why It Is Different From KV40 Or KV100
Kinematic viscosity measurements at 40°C or 100°C are still essential, but they do not represent the same stress state as a hot, highly sheared lubricant film. HTHS gives a more application-focused view of lubricant behavior under demanding operating conditions.
Why Formulators Watch It Closely
HTHS sits at the center of many tradeoffs involving wear protection, fuel economy, and specification compliance. Lower HTHS can support efficiency in some categories, while higher HTHS may be preferred where thicker loaded films are needed.
Why It Matters
HTHS viscosity is especially relevant in engine-oil discussions, specification compliance work, and any evaluation of wear-protection versus efficiency tradeoffs under real operating stress.
Related Concepts
HTHS Viscosity compared with Viscosity Index (VI)