OIl Viscosity Question

[PolarWhite]

Please, when will we ever outgrow this old school thinking? You NEVER EVER put anything in your car except what is written in the manual or on the oil cap. Some manuals even state that using other weights such as 10/40 or 20/50 will void the warranty. No where in your manual or any other vehicle manual does it say that the weight of oil depends on whether it is winter or summer. That is old school crap that your grandpa told you. Motor oil and engines of today do not even resemble the engines of yester year. You don't need a think gunky oil to fill in the gaps in the engine. Please tell him to stick to the correct oil. He is also hurting his gas mileage because 10/40 is not energy conserving.