Hey all, I just changed my oil in my Mazda 6i this past weekend and realized the car calls for 5w-20 however I already bought 5w-30 and put that in. Is this going to be a problem? I know it's a thicker oil but will it cause any type of issue? I'm just wondering if it's one of those deals where I should drain it and put in 5w-20 to avoid any damage. The car seems stronger with the fresh oil so not sure if it's just the oil change (Castrol Syntec Blend) or the thicker oil. Thanks for the input...

 

Well, I'm not exactly an expert, but this is what I have heard regarding the trend over the past 20 years to lower oil viscosity recommendations of car manufacturers for their new models. It is my understanding that engine tollerances have gotten tighter and that lower viscosity oil is required to ensure that the oil can get into these tight spaces. Regardless of the reasons however, I'm fairly confident that the manufacturers have done fairly extensive testing to determine what viscosity protects their engines the best. Considering the length of most car warrantees and the competitiveness of the market, it would only be in their own best interest to do so. So I think it is a good idea to stick with their recommendations.

In theory, a 5W-20 oil should have the viscosity of a cold 5 weight oil when it is cold and the viscosity of a hot 20 weight oil when it is hot. So, a 5W-30 should only be thicker than a 5W-20 oil once it has heated up to normal operating temperature in the engine. Since oil tends to become much thinner when it is hot than when it is cold, multiweight oils are designed to maintain a more consistant viscosity over a wide range of temperatures than single weight oils.

If your car is under warrantee, I would drain the oil and replace it with the recommended viscosity ASAP. If it is no longer under warrantee, I would probably let it go for 3,000 miles.
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