I have let 'er rip in the past. Now I will run them at 1/4 throttle for a couple minutes, then 1/2, then 3/4, finally full throttle, again for a couple of minutes. There may be debate as to how long the intervals would be but a little is better than nothing.
With it easier to make things to tight tollerance, there is less need to break-in.
After this short run time, listen carefully to the lok. If there is some squealing, a touch of oil may be needed.
There are a few topics covering lubrication on this great forum if you are the rare one that has a new lok that needs oiling right away.

Enjoy!

Thanks for the advice guys. I ran both engines fowards/backwards for about 15 minutes at about half speed and all seems (and sounds) fine.....

I usually do the same procedure for old or new locomotives. First I turn the wheels by hand to see if it is locked up. If it is loosing the casing and turning the wheels will free them preventing gear damage. I then oil the locomotive per instructions if I have them or else I oil the gears, wheel axels, and bearings/rotor. Then I run the locomotive at various speeds and also in reverse. Marklin used to use a oil that turned to wax, I had a crane freeze up because of this. I also oil my rolling stock in fact Marklin recommends this as they do not oil this at the factory. It also helps to keep a log of all your equipment when maintenance is done and what was done.

I don't run in my locos as I'm kind of doing it all the time. I mean I don't run them with fast speeds as it don't look prototypical. The only exceptions are my digitalised 3077 rail Zeppelin (with 6080 decoder) and E103 39579 with C-Sinus motor. They both have to go fast like their prototypes, but I have bought both of them as second hand.

I have one C-Sinus motored loco that don't go as fast as it should when comparing to it's prototype. It is DB E19 (39190). It's prototypes top speed was 180 km/h and my 39190 don't run so fast speed in it's 1:87 scale. Maybe my 39579 E103 don't run either 250 km/h or 283 km/h prototypical speed in it's 1:87 scale, but enough for me. 39190 don't run faster than say below 140-150 km/h if even so fast... Both locos top speed is adjusted to maximum speed setting.

I have adjusted top speed lower than max. speed in many other of my locos. I use all my locos except some 31859 or 31860 Crocodiles, so they don't get very much running time per loco. That kind of running-in period must do good for gears etc. My method works for me though. One thing is different in my "procedure". I use my locos to actually pull wagons, usually 10-30 per freight train or 5-10 per passenger train. This is done from new to get some load to motors and gears. This way the parts run in to the usage they were designed to.

PS. Does anybody know how long loco running should we excpect from these newer locos that have still brushes (drum commutator motor DCM)? Is it weeks, months or even years running time before service time for new brushes and so on? I know that Märklin recommends lubrication after 40 hours of running. In my use and different locos it can take years before this 40 hours running time is ended per loco...

Regards,
Janne

Hi!
Top speed for DB E 19 was 140 km/h (it was 180 km/h until the early '50s).

DB had no E 103 class. The top speed of their 103 class was 200 km/h (few locos were modified for higher speeds, but AFAIK not 103 137).