Dear Car Talk: Is it necessary to rev your Mustang several times before parking it in the garage? My neighbor insists on doing it, especially at 10:30 at night! – Dee
RAY: No, it’s not necessary, Dee.
Have you seen those TV commercials asking men if they have “Low T?” “Have you been feeling fatigued lately? Notice an increase in body fat? Rev your engine excessively?”
That might be what your neighbor is suffering from, Dee. He’s also suffering from NCM; Nostalgic Carburetor Mythology.
In the old days when cars were carbureted – the 1970s and earlier – all carburetors had something called a float bowl. The float bowl is not to be confused with a dessert you’d order at Friendly’s. The float bowl is where the gasoline was stored inside the carburetor while waiting to be released into the cylinders.
There was a myth (probably passed down from your neighbor’s grandfather to his father to him) that if you revved the engine before shutting it off at night, you would fill the float bowl with gasoline and therefore make the car easier to start the next morning.
But that was hogwash, even back then. Well, maybe it was true with his great-grandfather’s Pierce Arrow, but certainly not since.
First of all, the float bowl is already full when you shut off the car. It was designed to stay full, and it would certainly be full when you’re idling in your driveway, not demanding a lot of fuel.
Second, when you start the car the next morning, the fuel pump starts working the moment you crank the engine. So even if your carburetor is old and leaky and you lost some gasoline from your float bowl overnight, the fuel pump would immediately top it up and provide fuel for starting the car.
If your neighbor has a Mustang that’s 50 years old, he’s working off a myth that was never true in the first place. And if he has a Mustang built in the ’80s or later, then he’s got fuel injection, and even the debunked myth doesn’t apply to him.
Either way, there’s absolutely no mechanical reason for him to do this, Dee. Leave a copy of this column on his windshield and suggest he talk to his doctor.
Pump the breaks – this Subaru Outback needs work
Dear Car Talk:
I have a 2004 Subaru Outback, 6-cylinder. It makes a high-pitched humming noise, like millions of crickets, after I drive at freeway speed, but only after about 10 minutes on the road. It stops when I brake, then resumes. Oh, the Outback does have 272,000 miles on it. – Joy
RAY: Congratulations, Joy. It’s nice to see you marking the 50th anniversary of the moon landing by driving this car the equivalent of to the moon and part way back. Unfortunately, all you’ve got to show for it is a brake pad noise.
It sounds like you have a brake pad that’s sticking, causing it to rub against the disc rotor. Normally, the brake pads sit right against the disc rotors, and even touch a little bit, but not enough to slow down the car, or make any noise. Then, when you press the brake pedal, the brake caliper causes the pads to squeeze the spinning disc rotor, which is what stops the car.
Based on your description, it sounds like one of your calipers is sticky. So when you first start driving the car, everything is OK. But after about 10 minutes (and, more importantly, several applications of the brakes), the caliper fails to retract all the way, and leaves a pad pushed up against the rotor.
That’s what’s making the sound of a million crickets – the pad continually rubbing against the disc rotor as the wheel turns. When you actually use the brakes, and the pads are pushed tightly against the rotors, the noise temporarily goes away.
You should get this fixed, Joy. It’ll eventually get worse. The danger is that if your brakes are always lightly applied, you can overheat the brake fluid. And if your brake fluid overheats and boils, it can’t transmit hydraulic pressure, and your brakes won’t work.
Ask your mechanic to check your brakes. In particular, ask them to check for a sticky caliper. But when you go, bring some smelling salts with you. On a car this age, especially if the brakes have been neglected for a long time, you could easily end up needing $1,000 worth of brake work. You could need pads, rotors and a caliper rebuild.
But if that’s what it takes to make the car safe, do it, Joy.
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