The Insight uses the thinnest motor oil of any car we work on. Generally, thinner oil will reduce drag and improve mileage. This is not the only reason to follow Honda’s oil viscosity recommendations. The bearing clearances on the Insight are very tight, in order to "hold" the very thin oil. Thicker, higher viscosity, oil may not be able to fit into the small bearing gaps used on the Insight. A wrong oil choice at a quick oil changer could do some serious damage to your engine. Currently, the ONLY vendor of 0W20 oil is Honda, so that’s where we buy our 0W20 oil.