Q. I have a 1999 Audi A6 Quattro with 112,000 miles. The heater blows cold at idle but blows hot when I have my foot on the gas.
The coolant reservoir is full, the fans work, there are no signs of leaks, the dashboard gauge reads normal, and the water pump and thermostat check out fine. What's up?
A. Do you really mean that the heater blows cold? Or do you mean that it blows lukewarm - not hot enough to keep you warm?
You say that this problem happens only at idle, not on the road while in motion. If it is truly cold, there's something awry in the plenum and outside air is making its way in without being heated at all. Or perhaps the heater core is plugged.
I doubt that either is the case, though. If you are really getting air that hasn't been warmed quite enough, that is simply the way it is in some cars. The water pump doesn't route enough hot coolant through the heater core to heat the interior at idle. Why not? Because the water-pump capacity is high enough to keep the engine cool at wide-open throttle, and a high-revving engine simply doesn't spin the pump very fast at idle.
My suggestion is to use "recirculate" mode so you are at least reheating lukewarm interior air instead of fresh, frigid, exterior air.
Running the fan at low or medium will let the air passing through the heater core gain some temperature on its way through. The air coming from the vents will be warmer, if not quite warm enough.
Q. A friend of my mom just bought a new Volvo. The dealership told her that, because it was a turbo, she should never immediately turn off the engine upon coming to a stop. Instead, they told her, the car requires her to idle for two full minutes before turning it off.
A. When turbocharged cars first became common a generation ago, idling for a few minutes was a very good idea.
At shutoff, after the car had been driven hard, the red-hot turbine housing would cook the lubricating oil in the turbo, forming coke deposits in the bearings, which would eventually destroy them.
Within a few years, however, carmakers fixed this by water-cooling the turbo bearings. This kept the oil cool enough to prevent coking.
If this Volvo has a water-cooled turbo, she doesn't need to let it idle. All Volvos made after 1986 have water-cooled bearings.
Q. My car key is sometimes hard to turn in the ignition. What gives?
A. It's a common problem, as evidenced by the fact that twice in the past month I had to go out and help someone get his car started.
Here's the scenario: Get into your car and try to start it. The ignition key won't turn the lock cylinder. Try again, this time twisting the key hard enough to worry about breaking it off. Nope. Now you're going to have to call a tow truck to get your car hauled to the dealership.
Wrong. There's no problem.
You had shut off the engine while holding a little torque on the steering wheel, which left the front wheels slightly skewed. When you took out the key and the locking pin slid home, the steering column tried to straighten itself out. That put pressure on the locking pin, which made the key hard to turn. Simply wiggle the wheel back and forth an inch or two while gently trying to twist the key. This will unload the pin, and off you'll go.
Q. How can I renew my sandblasted headlight lenses? Winter highway driving has caused a poor view in the nighttime because of reduced headlight shine.
A. Funny you should ask. It's too long a process to describe here, but I wrote "How to Polish Your Headlights Like a Pro" for my "Saturday Mechanic" column in the March issue of Popular Mechanics. To read it, go to popularmechanics.com/automotive/how-to/4252611.html.
Mike Allen is a senior editor for Popular Mechanics magazine. Questions may be sent via e-mail to driveit@nytimes.com.
