Does this look like Zinc Pest?

I have a couple Amtrak Superliners that look like this as well, maybe not as bad but it's there. They still run fine so for now I haven't done anything with them, but I've wondered what it is...

Kind of looks like mold to me, but I'm not an expert.

If the metal is crumbling/cracking  it is zinc pest.

Unless you start to see unexplained distortion or crumbling (which would indeed be zinc pest), it might just be surface white rust, or "wet storage stain". The white rust shows up when zamac / zinc alloy castings are stored in low air circulation areas. (Like in a tightly closed box in an attic or basement ) Everybody has their favorite methods for removing it. Some use vinegar solutions, some use oil. 3-in-1 oil has worked for me on an old Lionel SG casting, but I can't say what would work in your situation.

I think it does look like zinc pest.

The green copper oxidation on the axles suggests it was wet, or stored in a damp location.  That's one of the conditions that is believed to contribute to zinc pest.  And the fact that Bobby has some that have the same problem strongly suggests a bad batch of zamac, or that these trucks as a batch were stored in a wet location before being mounted on the cars and sold to the public.

 I would bring this to MTH's attention, maybe they will send you replacement trucks.  Because if it is zinc pest it will only get worse, and the cars will eventually become unusable.

If it is indded zinc pest it will make for interesting junk load in a gondola. That's what I did with a pair of K-Line trucks with zinc pest. 

I see the white corrosion, which wouldn't be do bad, but the chipping strongly suggests zinc pest. If you can use a magnifying glass or zoom way in with a camera lens, bad zinc shows crystals at the edges where it's cracking.

Looks like corrosion to me - especially since the brass parts are corroding too.  Zinc pest usually leads to crumbling or total failure.

It doesn't look like Zinc Pest to me. Zinc Pest is usually deep into the metal, and causes distortion, swelling, and/or flaking.
It looks like a bit of surface corrosion, probably from getting wet.

Some others have written the same.

MDHeavener,  in your photo there is corrosion on the axles and on the pickup roller bracket, both of which are steel and would not be affected by zinc pest.  Your train needs a good cleaning.

This is zinc pest:

Thanks all that was very helpful information.

Zinc pest, (from German Zinkpest), is a destructive, intercrystalline corrosion process of zinc alloys containing lead impurities.^[1] While impurities of the alloy are the primary cause of the problem, environmental conditions such as high humidity (greater than 65%) may accelerate the process.^[2][3]

It was first discovered to be a problem in 1923,^[1] and primarily affects die-cast zinc articles that were manufactured during the 1930s, 1940s, and early 1950s. The New Jersey Zinc Company developed zamak alloys in 1929 using 99.99% pure zinc metal to avoid the problem, and articles made after 1960 are generally considered free of the risk of zinc pest since the use of purer materials and more controlled manufacturing conditions make zinc pest degradation unlikely.^[2]

Affected objects may show surface irregularities such as blisters or pitting, and they expand, buckle, tear, in an irreversible process that will eventually destroy the object. Due to the expansion process, attached normal material may also be damaged. Zinc pest is dreaded by collectors of old die-cast process model trains, toys, or radios because otherwise valuable items can be rendered worthless but for their residual parts. Engine parts of older vehicles or airplanes, and military medals made of zinc alloys may also be affected.

Zinc pest is different from a superficial white oxidation process ("Weissrost") that may affect some zinc articles, and is not related to tin pest.

My Mantua HO steamer kits from the early 60's were made of "Zamac", or so the ads(?)/reviews said. They are still solid as rocks. I have not seen the term "Zamac" in a long time. Were most Lionel PW steamers and other parts made from this? If not, why not? And why not now, with locos costing $1500? - "Chinese" or not.

Yes, Lionel cast their metal shells, such as steam engine boilers and the GG-1 body from ZAMAC. Many other parts were cast from the same material. It is a very popular material, and as far as I know, still in widespread use when a cast metal part is wanted.  There are a number of different formulations of the alloy, with differing characteristics. I find it interesting that there are only small changes in the composition from one alloy to the next.

From what I have read, much of the early work developing ZAMAC die casting was done for toys and trains.

Here is a site with interesting information on ZAMAC: Eastern Alloys

Here is another: Zinc Alloy Elements

Die casting was also developed for automotive carburetors that became complex castings in 1930s. Not all die cast zinc based alloys are problematic.