I have just started again on actual model railroading. I have been collecting for 15 years. None of my numerous engines have been run for more than a test in that period, as I collected them. None have been run at all in the last five years. Should I test them as I prepare to use them? What should I look for in the testing? The majority of my collection is N scale.
Place them on some track and apply power slowly. Some may take a little running before they smooth out. In rare cases, some of the lubricant can dry out and seize up the mechanize. It has to be cleaned out with a solvent and re lubricated. I personally have only seen this happen in Z scale Marklin locomotives.
I've been digging deep in my locomotive box and running locos that haven't seen the light of day for a few years. Most will run just fine after a few minutes of run time. A few have needed a little oil, and none have not run at all. If any make loud screeching noises, they need to be lubed.
Since the engines have not been run, they probably do not need cleaning. Before any significent running, I recommend removing the body shell, and placing a small drop of light weight lube oil on each of the motor bearings, and the drive shaft bearings.
I would put them on the track and start to run them slowly. Try to switch pulsed mode on and off if your throttle allows (I use a MRC Tech 2400). Don't run other trains that would distract your attention. What I do is listen to the engine. Does it make strange noises, is there a bearing screeching, is there a funny smell, does it become hot? I would first try and test it, and then decide about cleaning, lubrication, etc.. My "sickest patients" are some Atlas-Kato engines that suffer of bad electrical contact due to oxidation. So far I could not fix this problem.
