This is such a debated thing. Ask any dealer or non-engineering person and they will say that technologies so good these days that running in is no longer necessary.

IMO that is total bollocks.

Yes the technology is there to machine metal to tolerances of many microns but the tooling, technology and time to do so would push the cost of producing a car like the Fiesta up by many, many thousands of pounds.

At the end of the day when you have moving parts that work against each other (particularly metal against metal) then there is always some bedding in to be done. Mainly this is the piston rings, oil control rings, crank bearings as well as dozens of other components. It is therefore important that:

- The car is warmed gently but promtly - don't just leave it idling on the drive
- Be gentle on the revs until full operating temperature is achieved. Remember that even if the water temperature is up to normal the oil temperature is still waaaaay behind!

The above two apply even once run in.

During the 1000mile running in period I personally:

First 500miles
- Don't rev passed 3.5k except on very rare occasions just allow it to 'blip' up to 4-5k. Keep this brief, say in second gear.
- Don't allow the engine to labour in any gear. By this I mean don't have the engine struggling in a gear e.g. 1000rpm in 3rd
- Don't use full throttle.

500-1000miles
- Same as before but up it by 1000rpm. 4.5k through the gears and allow it to blip up (occasionally!) to 6k.

After that, have fun. By the way, jumping on the M25 and doing a couple of laps doesn't count. Varying speeds are the key to a well run in engine.


This is the way I personally do it. You have to remember that you won't really reap the benefits unless you keep the car for several years. If you rag it hard from the start cars do seem to run quicker but in later life it will use more oil and probably sound less sweet.