What Does Engine Oil Shear Value Mean?
4 Answers
Engine oil shear value indicates the oil film strength of engine oil under high shear conditions at 150℃. The higher the value, the greater the strength. Below is an introduction to related content: 1. German cars: Most German cars require HTHS to be greater than 3.5. 2. French cars: Most French cars require HTHS to be greater than 3.2. 3. Others: American, Japanese, Chinese, and Korean cars generally have a basic HTHS requirement of around 2.9. 4. Frequent aggressive driving or long-distance high RPM: For example, driving frequently above 3000 RPM, the requirement for HTHS should be increased. It is recommended to use engine oil with HTHS>3.5.
Oil shear value actually refers to the oil's resistance to being forcefully squeezed between components. Take the crankshaft bearings and cylinder walls as examples—they endure tens of thousands of compressions per minute. If the oil can't withstand the high temperature and speed, thins out, and the oil film breaks, it's disastrous: metal grinds directly against metal. That's why for high-revving or turbocharged cars, I always recommend paying attention to the HTHS (High-Temperature High-Shear) viscosity parameter—make sure to choose oil with a value above 3.5cP. I've seen cases where people used low-shear oil improperly, resulting in grooves worn into the camshaft. The repair costs were painful.
I understand the oil shear value as the oil's pressure resistance toughness. Imagine the moment when the piston rings scrape against the cylinder walls, the oil must withstand pressure tens of thousands of times higher than gravity within five thousandths of a second. A low value means the oil film is prone to rupture, especially during summer traffic jams when water temperatures soar and the oil thins out—the engine's rattling noise is a warning signal. For maintaining my German turbocharged car, I always check for the ACEA C3 certification, which explicitly requires a shear value ≥3.5. Here's a handy tip: oils with VW502/505 or BMW Longlife-04 certification on the cap generally meet the shear value standards.
Plain English explanation: Shear value refers to the oil's ability to resist being squeezed flat. When gears mesh, they generate scissor-like forces. Oil with high shear value acts like a strong rubber band—it quickly rebounds after being stretched to prevent dry friction. This parameter is especially critical for older vehicles—I've seen a 120,000-km Buick where valve noise disappeared immediately after switching to high-shear 5W40. Beware of marketing hype: some so-called full-synthetic oils actually test at just 2.9 shear value, worse than mineral oil. How to read packaging: In API SN ratings, later letters (e.g., SP) generally indicate higher shear values.
