Engine Break in Question

[logic23]

Hello, I recently rebuilt a couple 2.5 SOHC 2001 engines.  (new bearings, reground rods and crank and new pistons)

What is the correct procedure for breaking these engines in. 

Automatic transmissions in the cars they're being installed in.

Thanks

[Fairtax4me]

The biggest worry wih modern engines is keeping fresh oil on the cylinder walls so the rings seat properly.

Generally you want to run the engine at about 1,500 rpm for 15-20 minutes while keeping an eye on oil pressure and coolant temps. Then shut it off and let it cool.

 

You can choose to change the oil and filter after the initial run, or wait until after the first drive. After the engine has cooled, start it, let it warm up again at a high idle, (3-5 minutes is fine) then go for an easy drive around the block a few times. Avoid idling (sitting in traffic) for long periods. Try to go about 5-10 miles at mixed speeds, just don't run the engine really hard, keep the RPMs under 3500.

If you have trouble with the engine stalling, disconnect the battery for a few minutes and reconnect it while the engine is still warm. Then start the engine again and let it idle so the ECU learn its idle AF mixture. Don't touch the throttle for about 3-5 minutes. Then take it for a short drive.

 

At this point you'll want to do an oil and filter change (a second if you did one already).

 

After that you should be good to go, just drive easy for about 500 miles. Try not to use more than about 75% throttle. After 500 do another oil change, then you can drive it however you want.

[keith3267]

The old school way of breaking in a rebuilt engine, which worked for manual transmissions of the day, was to take it out on the road and do ten 30-50 (50-80kph) runs in high gear at full throttle.  This would seat everything right away.  Then back to the shop for an oil change.  Its really difficult to reproduce those parameters today.

 

The key is to put as much pressure on the rings as possible to get them to seat.  Never run the engine at a constant RPM for any length of time and do not run at high RPM or allow it to overheat until it is broken in.