Evaluating Oil Viscosity Claims: Data vs Opinion

The speaker critically examines claims made by another channel regarding engine oil viscosity grades, referencing both industry standards and a dataset exceeding 10,000 used oil samples from Speed Diagnostics. Three primary claims are addressed:

1. For identical engines, the US-recommended viscosity grade differs from other countries due to Corporate Average Fuel Economy (CAFE) requirements. This is confirmed, as seen in previous videos covering 0W8 oil for Toyota Corolla and the GM L87 recall, where engines in the US use 0W20 while other countries recommend higher viscosity grades like 5W30. Lower viscosity in the US is selected to meet fuel economy targets, but OE recommendations outside the US validate that higher viscosity can be used safely.

2. The assertion that 0W20 oils shear down and lose viscosity faster than 5W30 is refuted by data from over 10,000 used oil samples. The analysis finds 5W30 oils are "twice as likely to shear out of grade than 0W20 oils," with over 40% versus 20%. While both can shear out of grade, when 0W20 stays within grade, wear protection is slightly better than 5W30, though differences are not statistically significant. However, once 0W20 shears out of grade, wear increases, making shear stability more critical than grade alone. The split between numbers in oil grade is flagged as important; a wider split (e.g., 0W20 vs 5W20) usually means less shear stability.

3. A claim that 5W30 oil produced "40% less wear than 0W20" in identical engine tests lacks substantiation. No supporting used oil analysis data, mileage, oil brand, or specs were provided. Speed Diagnostics data shows brand and shear stability vary, with some brands staying in grade and others not. Real-world findings indicate 0W20 can match 5W30 for protection if viscosity stays in grade. Higher viscosity doesn't always reduce wear, and in fact may sometimes increase it.

Key recommendations: Always start with OEM oil recommendations, and use oil analysis to determine real wear rates (e.g., "less than five parts per million per 1000 miles" for wear metals is optimal). If oil shears out of grade or wear metals rise, switch brands or opt for an oil with a narrower viscosity split. Shorter oil change intervals do not guarantee grade retention. Fuel dilution and injector health significantly impact real-world viscosity.

The central takeaway: prioritize used oil analysis data over unsupported opinions and claims; seek oils with proven shear stability.