When it comes to crud on rails and wheels, I’ve learned a thing or two over the years.

1. The number-one producer of rail & wheel crud is the electrolysis effect of passing current through dissimilar metals. Where our current-drawing locomotive wheels (of one metal) meet the rails (of another metal), a very fine powdery oxide is formed. In "a Perfect World", this oxide would just powder over the edge of the rails and never be a bother to anyone. These days, most of our rails are made from nickel-silver because the oxides of this metal are a bit more conductive than the oxides of brass and, therefore, nickel-silver just seems to stay cleaner longer. You all have probably seen advertisements for locos with nickel-silver wheels and the ads from Northwest Short Lines for replacement/substitute nickel-silver wheels. This is, generally, a very good trend because it puts both rails and wheels of the same metal at the point of current pick-up and minimizes the oxide production. (Nickel-silver wheels on non-power rolling stock don’t really prevent anything, but they’re nice to look at).
   
2. In our Non-Perfect World, over-lubrication, humidity, cooking vapors, smoking, forced hot air heating, wood stoves and fireplaces all contribute to an environment in which the oxides tend to bind together and also to wheels and rails. Conditions vary, from layout to layout, and the mess can be seen as decreased engine performance, headlight flickering, scratchy sound systems, spotty DCC operation, film that’s almost invisible, a thick "tire" on rolling stock wheels and, in some cases, crossings and switches that stall out the engine because the points seem to concentrate a build-up of crud in those places.
   
3. "Normal" house dust, dander, baby dust bunnies, cat hair, smoke particles and sawdust all get mixed into the formula and bind with the oxide crud to, in some cases, create a truly impressive challenge.
   
4. Scratches on the rail heads or wheels, from abrasive cleaning, gives the crud a place to "root" to and build up from there and will be seen as patches of crud in various places along the way.
   
5. Non-powered rolling stock wheels (metal or plastic) are a vast storehouse of accumulated crud. I agree that plastic seems to accumulate faster than metal, but it’s all a matter of degree. A thorough cleaning of the rails is a positive thing, but with dirty wheels, the effect is negated very quickly because of re-deposit back onto the rails.

My solution, for many years, to all of this has been to use non-abrasive rail & wheel cleaners. The most efficient arrangement has always been to run a "wet" one ahead of the engine, to ensure that it never has the opportunity to stall on crud spots, and a "dry" one at the back to pick up all that dislodged wheel dirt that was loosened by running through a film of cleaning fluid. The drivers are automatically and thoroughly cleaned and the following storehouse of wheel dirt is eliminated, as well. It usually takes several passes (and in worst case - several roller covers) to get it all.

NOTE - It doesn’t do much good to clean only until the engine runs well - and then not finish the job. (Do the job right and get ALL of the rail and wheel dirt).

There has been controversy for years as to what fluids are best, but here are some researched guidelines.

1. Water based fluids sort of work. ‘Problem is - they leave residues that don’t go away, that tend to bind the oxides together and then harden and only cause the need to clean more often. This class of fluids includes Windex, 409, Fantastic, Simple Green and that "blue stuff" that you see in hobby stores. Some of that stuff can corrode rail joiners and the pivot area of switches where it has seeped inside or underneath.
2. Oil based fluids can be very useful, if the right oils are used. First rule of oils is to NEVER use an automotive lubricant. As an example, the removal of 10W30 from the rails and wheels is nearly impossible and that stuff is really slippery. The best oils to use (if you like oil) are ones like Wahl’s Clipper Oil, Sewing Machine oil or Starrett oil. These are all highly refined mineral (instrument) oils, are relatively thin and will NOT lead to corrosion problems. There is a "legend" that these oils are conductive, but that is absolutely not true. What IS true is that these oils tend to soften or liquefy the cruds that we contend with so that locomotive wheels do get good direct electrical contact with the rails through the oily film. These oils take "forever" to dry, so the effect is fairly long lasting. A light film of any of these oils can be quite useful in preventing oxidation of the rails on a layout that will be left unused for some time in a corrosive atmosphere (laundry room, salt air, etc.) and these oils can easily be removed from rails and wheels with a good (solvent) track cleaning fluid.
3. Solvent based fluids are, usually, the most efficient to use and (good or bad) there are a great plenty to choose from. Some solvents are just plain dangerous to use and/or can attack the plastics that are an integral part of model railroading. These "bad" solvents include lacquer thinners, acetone, naphtha, tri-chlor, carbon tetrachloride, etc. and are, of course, to be avoided. Fast-evaporating solvents such as Tuner Cleaners, alcohols, Contact Cleaners, etc. work well for as long as they are fluid but, by their nature, they are gone again almost immediately. I have found that the best solvents to use are the (non-toxic and non-explosive) slowly evaporating fluids such as mineral spirits, white spirits, Goo Gone, Aero-Locomotive Works Fluid, etc. These fluids stay fluid long enough to do the job well and leave a clean metal-to-metal contact for the locomotive drivers resulting in maximum traction, excellent electrical contact and great slow-speed operation. The idea is to clean your rails and wheels right down to the "molecules" (without harming anything) and not leaving any unwanted or harmful films or residues.

Smooth slow speed operation of trains is a combination of many factors, not the least of which is clean rails and wheels. Over the years, I’ve had several "cheap" locomotives that would do two-ties-to-the-minute speed and this is how I do it.