Reasons for disappearing smoke are clean and clear

Dear Car Talk:

I’m 71 years old and have noticed that very few passenger vehicles on the roads today smoke from the exhaust pipe anymore.

Years ago, it was very common to see cars, even relatively new models, smoking like a mosquito fogger. Why is that? I doubt it’s because of better maintenance nowadays. — Frank

Yeah, my brother used to drive a ‘74 Chevy Mosquito Fogger. You’re absolutely right, Frank. It’s unusual, and even somewhat offensive now to get stuck behind a car that’s blowing smoke out the tailpipe. Why is that? I give credit to three major developments. The Clean Air Act, Japanese cars, and better oil technology.

Let’s start with the Clean Air Act of 1970. Forced to clean up their tailpipe emissions, car makers phased out carburetors. Carburetors were crude devices. They weren’t much better than pouring gasoline into the cylinders from a boot. When excess gasoline went into the cylinders, it couldn’t be combusted completely, and came out the tailpipe as black smoke (and smog-producing hydrocarbons).

Over the next decade or so, fuel injection replaced carburetors. Fuel injection measures the fuel much more precisely, and when combined with computer controls and instantaneous feedback from sensors, it really solved that “excess fuel” problem.

The second reason for smoke was poor manufacturing tolerances. Tolerances are the spaces between parts — also known as “slop.” The more slop, the poorer the manufacturing. Japanese companies, particularly Honda and Toyota in the ‘70s and ‘80s, revolutionized engine manufacturing, with much tighter tolerances. That made their engines more reliable and longer lasting. It also left less slop between the pistons and the cylinder walls. When there is slop between the pistons and cylinders, lots of oil remains on the cylinder walls between piston strokes, and gets burned up with the gasoline. That oil also comes out the tailpipe, as blue grey smoke.

In fact, my late brother used to pull his ‘74 Mosquito Fogger into a gas station and ask the attendant to “fill the oil and check the gas.” But once the Japanese jumped ahead in quality, the rest of the world knew they had to catch up, so eventually, all cars ended up with better tolerances.

Finally, oil used to be a lot thicker. You may remember 50 weight oil, or 10W40. That thicker oil was harder for the rings to scrape off the cylinder walls, so it was more likely to get combusted and turned into smoke.

Now, we have oils that are not only lighter, but better at lubricating, too. And because they’re lighter and thinner, less of that oil adheres to the cylinder walls, meaning less gets burned up and sent out the tailpipe as smoke.

Now, if you write again in 10 years and ask me the same question, I’ll probably add the rise of electric vehicles to my answer. You’ll never see any smoke coming from an electric vehicle. Unless the battery catches fire.