Makeshift Mechanics

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Sunday, April 19, 2009

Dear Tom and Ray:

My daughter-in-law just sent her son out to wash her car's brakes. She said that when her brakes start to squeak, she gets her son to wash the accumulated dust out and they stop squeaking. She said you can see the water coming out black for a while, then when the water comes out clear, the dust is gone. Is this for real? -- Marie

RAY: We've never heard of this either, Marie.

TOM: What she's having her kid do can't really hurt the brakes, unless it's done while the brakes are hot. Then the cold water could warp the rotors.

RAY: But otherwise, it's a harmless exercise -- the brakes are designed to shed rain and road water -- I'm just not sure it's doing much good.

TOM: Right. You can put the hose on the outside of the wheel and rinse off any loose dust on that side of the brakes. But it would be very hard to get to the other side (the inboard side) of the brakes.

RAY: Normally, when someone comes into our shop with squeaking brakes, we remove the rotors and all the pads, and deglaze everything with an abrasive. But who knows? Maybe the hose is doing a much more rudimentary version of that.

TOM: And if it works, why not?

Dear Tom and Ray:

A group of us get together at a diner for coffee most mornings. Recently I made a critical error and told the guys that I had put a piece of cardboard in front of my radiator for the winter. So, when it's 20 below zero, my Toyota warms up quickly. My friend -- our resident pseudo-engineer -- explained that the thermostat in the cooling system handles all that stuff, and that any participation on my part, by adding cardboard, is completely unnecessary. He convinced the group that he was right. But is he? -- Joe

TOM: No. He has his head up his radiator hose, Joe.

RAY: Here's a basic description of how the system works. Most engines run most efficiently at about 200 degrees Fahrenheit. So the coolant just stays inside the engine -- and does not get sent through the radiator -- until that temperature is reached.

TOM: Then the thermostat opens, allowing some of the hot engine coolant to flow through the radiator, where it gets cooled off by the cold air blowing through it. By opening and closing like that, the thermostat keeps the engine in its most efficient temperature range.

RAY: When the ambient temperature is very low, it takes longer for the engine to reach operating temperature. And then, when the thermostat finally opens and allows the coolant to flow into the radiator, the ice-cold coolant that had been sitting in the radiator then gets pushed into the engine, lowering the engine temperature far more than necessary.

TOM: So when it's bitterly cold out and you cover up the grill with cardboard, you're preventing the frigid outside air from blowing through it, and keeping the coolant inside the radiator from dropping to the temperature of the outside air.

RAY: On another note, we made a dumb mistake a couple of weeks ago. We were trying to help a woman whose mechanic had put coolant in her windshield-washer reservoir, and it was greasing up her windshield. We told her to drain the washer reservoir, and then add some windshield-washer concentrate.

TOM: But we apparently wrote "coolant reservoir" instead of "windshield-washer reservoir." We apologize for any confusion.

Got a question about cars? Write to Click & Clack in care of The Post, or e-mail them by visiting the Car Talk Web site at http://www.cartalk.com.

2009 by Tom and Ray Magliozzi and Doug Berman


© 2009 The Washington Post Company

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