Slight loss in mileage. Many autos oils are low viscosity, 5W-20 or even 0W-20. If you use a heavier oil you may loose mileage. This has to do with the engines crankcase pressure. Heavier oils can increase the engines crankcase pressure and this creates greater resistance on the pistons downward stroke. The piston is pushing against greater pressure. So with Hy-Per Lube being so thick it can also lower your cars mileage. I have noticed a slight loss in mileage but because my truck is 22 years old and has more than 150,000 miles on it, I’m more concerned about the longevity of the engine. I have noticed less oil consumption.