Do you still need to "blow out the cobs" from time to time?

Dear Car Talk

Dear Car Talk | Sep 01, 2009

Dear Tom and Ray:

I know we are supposed to drive our cars gently ... accelerate gently, brake gently, etc. But is there any benefit from occasional and brief full-throttle blast, for, say, a mile or so? As a boy in the 1960s, I recall my dad and my friends' dads making reference to "blowing out the cobs," like it was something the family sedan needed every now and then. It may have been a reference to something else that sounded like cobs -- I'm not really sure. So, my question is multi-part: Are you familiar with this expression? Do you know the correct version and its origin? Was it ever good for a car? Should we be doing it today? I hope you can clear up this "cob" mystery.

-- Terry

P.S. As a teenage driver, I saw to it that the engine in Dad's car was completely free of cobs.

RAY: Great question, Terry. You must have grown up in the Midwest, where corn seedlings often got blown by the wind into people's exhaust pipes. And due to the heat and moisture there, corn stalks would often sprout and, ultimately, produce corn.

TOM: And you had to drive fast once in a while to "blow out the cobs." This was most problematic in August and September, during harvest season, of course.

RAY: We're pulling your leg, Terry. The phrase is "blow out the carbs," as in "carburetors." And here are the likely explanations:

TOM: Back in the 1960s, some high-performance cars had four-barrel carburetors. If you drove slowly around town, you'd use only two of the barrels. In order to exercise the other barrels -- the high-speed barrels -- and keep them from potentially sticking, you'd have to get the car out on the highway and accelerate hard for at least a short time.

RAY: The other explanation is that, since carburetors ran so rich, the extra fuel they poured in would lead to carbon buildup on the pistons. And the thought was that by running full throttle, you could heat up the pistons and burn off some of the carbon. So the carbon may have been the "carbs" that some people were referring to.

TOM: But mostly, "blowing out the carbs" was an excuse to drive fast -- as you ably figured out on your own, Terry. And it's certainly not necessary now. In fact, it's dangerous, and a waste of fuel.

RAY: All cars now have fuel injection, in which the fuel is carefully and precisely metered by the computer. So there are no carburetors to blow out, and there shouldn't be any carbon buildup on the pistons.

TOM: So if a policeman stops you for speeding, saying you're "blowing out the carb" will not get you very far, Terry.

RAY: Yeah. You might have better luck telling him you're trying to make it to the farmer's market before it closes, because they're having a "blowout on cobs."

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