10W30 Vs 15W40

10W30 Vs 15W40 Engine Oil If you’re in the market for new engine oil, you’ve probably noticed that there are two different viscosities: 10W30 and 15W40. What does this all mean? The oil’s viscosity determines how quickly it will flow. The lower the number, the easier it will flow. If you’ve got a high-performance engine and …

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