Can't get through seemingly permanent dust and grime

Over time, some of that grunge may have chemically reacted with the paint or the plastic surfaces, making it difficult to remove. Stripping and repainting may be the only options.

Remove the shells and wash with mild dishwashing soap and soft brush, then rinse and let dry.

Passing a wet rag removes some dirt but leaves a residue. 

What about blue masking tape?  Or even rubber cement.  Put a dab on a piece of cardboard and let it dry.  Then peel it up and roll it into a ball.  Would it "pick up" the dirt?  Heck, you could even try Silly Putty, I don't believe it would "stick" or cause any harm.

Wes97 posted:

I've got a few dirty postwar Lionel engines and cars, and the decades of grime seem to have a real hold of these cars. I've got a 600 NW2 Switcher with some weird whitish water stains that disappear when I'd wipe it with a damp rag, and would reappear as soon as it's dry.

I've also got a few dirty tenders with brown dust in all the crevices and soapy water, toothbrushes, and canned air don't seem to have any effect on.

Anyone have any suggestions on how to tackle this?

For the tender, dishwasher soap and tooth brush.

He did state he already tried a toothbrush with soapy (detergent?) water and dust-off air to no avail.

Tinplate Art posted:

He did state he already tried a toothbrush with soapy (detergent?) water and dust-off air to no avail.

I did use a toothbrush but I should have specified I may have used a dish soap. Since I can't remember I may try again but I'm really looking to find any kind of soap or cleaning agent that's as strong as it can get without hurting paint or plastic.

Maybe a little lemon pledge and a soft rag.

If repaint is your only alternative, then i usually apply more pressure and stiffer bristles on the brush.  I've never encountered the permanent grime but have seen discoloration due to a reaction.  If decals or lettering are in the area your choices are limited.  You can test the chemical reaction of your cleaner on the inside of the shell.  I always take the shell or casting off and work with it separately. 

The white spots on the engine shell may be light calcium / lime deposits.  Use of white vinegar or lemon juice on dishes removes the deposits.  

I'm not certain if these options are harmful to plastic.  May want to try it on something that has no value to see what if anything it may attack. 

The white may be an instance of the mold release agent, sometimes seen on scout trucks, and (leaching thru the paint) on NYC F3s. If so, it should liquefy with gentle heat from a hair dryer, and then wipe up with a rag.

I had a tender with the dark brown on it. I suspect it is tar from tobacco smoke, fused with decades of cardboard box fuzz inside a warm attic. Just a guess. What I know for certain is that I ended up having to gouge the stuff out with toothpicks, after softening it up with soapy water. The gunk collected in the crevices is only the worst of it. The whole shell had a brownish haze. In the end, I had to go over the whole thing, meticulously, three times to get it to where I was happy. That was a prewar Flyer cast metal tender with no coal load and hardly any rivet detail, so you may find yours even harder to clean than mine was. Given the condition of the lettering, I'd be very tempted to just strip and repaint this one, unless there is something special about it that I can't see in the photo.

Try some dishwasher rinse like Finish or Cascade. 

What you have is the result of mold or mildew attacking the paint. Not uncommon on post-war paints. No know fix.