Saturday, March 30, 2013

More Car Talk "Chemistry"

Regular readers know my fascination for all things NPR, and Car Talk in particular. This week's broadcast had me rolling in the aisles for a different reason: some cover-your-eyes-awful chemistry.
A "white residue" in the engine?
Get the peanut butter!

Let's set the scene: Tom and Ray had taken a call from Ann, who begged that they were her "last hope" for an aging, ailing Subaru wagon. Ann's son apparently noted a funny white "mist" coming out of the car a few months ago. After several expensive repairs (heater core, radiator), a white, powdery substance was still forming in the engine block.

The guys considered that a single engine part had failed, perhaps something plastic or rubber, but discarded that theory since previous repairs had not fixed the problem. Then Tom suggested that the car might be continuously producing the white residue, perhaps through combustion gases which found their way into the radiator fluid through a leaky gasket.

Tom short-listed some potential combustion "bad actors" - carbon, carbon dioxide, carbon monoxide, nitrous oxide. Aha! The nitrous oxide must be forming nitric acid, thus corroding the engine block. "It's Chemistry 101!" he exclaimed.

Except...not. I know that nitrogen dioxide or NOemissions from cars generate nitric acid in the presence of water, but last I checked, whipped cream cans and dental offices everywhere remained safe from acidic corrosion.

Undaunted, through admitting "I have no idea, I'm just making it up," Tom pressed on: perhaps a salt, such as copper nitrate (a blue solid) or, even better, copper carbonate ("It just sounds more white, like sodium bicarbonate") gummed up the works. Maybe, since the heater core was made from aluminum, that was the culprit?

Tom: "What about aluminum carbonate, A-L two C-O three!"
...or, maybe Al2(CO3)3?

Finally, Ray chimed in: "MIT's on Line 1, they want their diploma back."

Happy Saturday,

Note: I paraphrased this conversation as best I could, since the recording hasn't yet appeared online. When it does, you can hear the full 3/30/13 episode at


  1. Ok smartiepants, then what WAS the substance?

    1. Oh, I'm right there with them on it being a metal salt. Off the top of my head, white, flocculent salts that could form under those conditions?

      aluminum hydroxide
      alumina (aluminum oxide)
      dry copper sulfate
      various zinc salts (from washers, fasteners, clamps)
      various magnesium salts

      No dice on copper nitrate, copper oxide, copper carbonate, or iron salts, since most of those would be colored (blue, black, green, or red)

      A quick test for solubility would help a lot. Does it go into water? Acid?
      It's likely a metal salt. Greasier solvent, like propanol or paint thinner? It's likely a plasticizer from a dissolving hose or gasket.

  2. Pretty sure most of this conversation left a lot of listeners baffled. But if you do think about it, everything that makes a car run is chemistry. From the anti-freeze and coolants to fuel combustion -- we just don't recognize all the scientific jargon. Haha!