What is a turbocharger...and is it an asset or a liability?

Dear Car Talk

Dear Car Talk | Dec 01, 1998

Dear Tom and Ray:

I'd like to know something about turbochargers on cars. Specifically, what is a
turbocharger? What does it do and how does it do it? Finally, is it an asset or
a liability on a used car? -- Peter

RAY: Good questions, Peter. A turbocharger is known in the parts department as a
"3BP." That's "triple boat payment," because it usually costs well over $1,000
to replace.

TOM: A turbocharger is basically a high-speed fan driven by the car's own
exhaust pressure. When you step hard on the gas, the exhaust spins the fan very
quickly (at tens of thousands of rpm) and the fan forces extra air into the
cylinders. When you force in more air, you can then burn more gas and end up
with ... more power!

RAY: In theory, it's a great idea. Engineers figured out that, for the average
driver, there are only a few times each day that you really need a lot of power
from your engine -- like when you're getting on a highway or passing a car on a
two-lane road. So why lug around a big V8 or even V6 engine, and pay the gas
mileage and pollution penalties that go along with that, when 97 percent of the
time a smaller engine would be just fine?

TOM: And, the theory goes, to add that extra surge of power when you really need
it, you call on the turbocharger.

RAY: The problem in reality is that the people who buy turbocharged cars tend to
be testosterone-poisoned males who have the turbo working all day long. And
that's hard on a) the turbo, and b) the rest of the car.

TOM: Also, most cars with turbos tell you to let the engine idle for 30 seconds
before you shut it off. And most turbo owners do this for the first week or so
they own the car and then forget about it. That idling time allows the oil to
cool off the turbocharger. If the turbo doesn't cool off, oil can eventually dry
out up there and restrict the passageways. That leads to turbo failure, and the
aforementioned 3BP.

RAY: So since turbos are rarely used judiciously or properly, we caution against
buying one in a used car. Of course, if you find a Mitsubishi 3000GT Turbo for
sale by a little old lady, you can take a chance on it. But even then, I'd be
willing to bet she's known around the nursing home as Grandma Leadfoot.

* * *

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