Why You Should Change your Oil every 9,000 miles

There’s a lot of religion and dogma about motor oils – both on the street and on the track. We thought we would apply some science to it. We’ll explain why it’s okay to change your oil every 9,000 miles with some oils and every 5,000 with others. The differences will surprise you.

When you pull apart an engine that’s had super cheap oil changes at the manufacturer’s recommended interval (normally 6,000 miles or more), you can instantly tell. Some engines will have clumps that feel like canned mushrooms in your oil (gross!). In spots, it will burn and deposit a thick coating on parts (think about the bottom of a pot of chili that was left on the stove too long). Clumps or solids are REALLY bad for the engine. The engine needs oil at the proper thickness to function. If it’s clumpy, it won’t flow to all the parts. Small passages might get blocked entirely.

Better performing conventional oils do the same but break down at much higher temperatures and over longer periods of time.

Also, remember the old myth that states you should change your oil every 3,000 miles? Even the worst oil will last 3,000 miles in your average car. But why not spend a few dollars more and change the oil half as often?

What about synthetic oil?

Marketers will have you believe it’s up to 15,000 miles or more. While that might be true for some engines, heat and chemical breakdown normally isn’t the limiting factor for synthetic oils. The limiting factor becomes contaminates.

Newer engines are much better at burning everything and leave less “stuff”. So, while I wouldn’t go 15,000 miles between full synthetic oil changes in a 1964 Cadillac, I might consider it in a new hot hatchback.

So, what do we recommend?

Thanks to attorneys, I can’t tell you which oils are terrible. I can tell you that Castrol GTX is a good conventional oil for daily drivers without turbos. There’s a reason why you see it called out by name on the refill cap of some high-end cars. I use Mobile1 for full synthetic when it’s needed, but I haven’t tested a lot of other oils. We’ve found that it’s the only oil that holds up.

 

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