Breaking in a New Truck

I’m buying a new diesel jeep next year and I have a couple of questions.

I have heard (but never read in an owner’s manual) that when you first buy a vehicle you should not exceed a certain speed for X number of kilometres. Apparently the engine metal needs time to be tempered or something. Is this true? And is it the same for both diesel and gasoline engines?

I have also heard (again, never read) that vehicles which aren’t sometimes driven at high speeds will never reach their full power potential. So, I guess, if Granny gives you her old car and she’s never driven faster than 60km/hr then you’re not going to be able to fly down the expressway at 140 or anything. Does anyone know if this is true?

I just bought a new car, and my owner’s manual says not to exceed 4000rpm for the first 1200 miles. When my mom got her new car a couple years ago, her owner’s manual said not to exceed 50mph for the first 500 miles.

I can verify that owner’s manuals do indeed tell you to give the car time to break in, but I’m not exactly clear on why. I figure I better follow along though because I don’t want any problems with the car. I’m sure someone much more knowledgeable in cars will come along soon.

These two Car Talk columns address those questions:


Your owner’s manual and the dealer can tell you the manufacturere’s recommendations. Modern manufacturing techniques have just about eliminated the “break in” for most engines. An oil change after 500 miles is common. And most manufacturers will tell you not to run at constant speed for long periods during the first 500 miles but rather to vary the ripm during driving.

But again, follow the directions in the owner’s manual.

Thanks, that’s useful information.