Finger-drawn "wash me" signs pop up on grimy cars in winter.

Donna Pirotte doesn't let that happen to her sport-utility vehicle, especially when salt and sand rule the roads. Friends always comment on her shiny SUV. And it's black, no less, the most challenging car color to keep clean.

"I make it a priority because that's how I was raised," Pirotte says. "My dad always said a car is the second biggest investment you'll make, and a car is a reflection of a person. I agree, but it's become increasingly hard in recent years, with having three kids."

Mark Thorsby, executive director of the International Carwash Association based in Chicago, recommends Kansas and Missouri motorists wash their cars at least three times a month in the winter.

People should wash the car as soon as possible after a snowfall. "Winter is the nastiest time of year for a car's surface," he says. "So if it isn't washed and then it warms up, the greater the corrosive activity."

In the Midwest, people need the undercarriage wash, Thorsby says. But people can skip the underbody rust inhibitors. "They're an imprecise product," he says. "So they're not terribly effective."

A few days after a snowfall, auto supply managers say they sell a lot of spray-on wheel cleaners. Customers tell them they don't want their wheels to rust. Armor All Car Wash wipes are also one of the top sellers in winter. People can use them while their car is parked inside the garage, but they're best for spot cleaning or wiping off a car surface when it's just a little dirty.

Auto dealerships keep their cars squeaky clean year-round. They polish cars in the beginning of winter and after winter. They wash them every few days, too. "When it comes to drying cars in the winter, it's a good idea for people to wipe off the weather strips around doors so they don't freeze shut," says Rich Frost, service manager of Cable-Dahmer Chevrolet in Independence, Mo.

Car interiors also need extra care during winter. Ice-melting chemicals eventually rot plastic, leather, vinyl and fabric. The salty water also damages the carpeting and floor mats unless they're vacuumed soon after they're wet, Thorsby says.

An incentive for cleaning a car in winter is the resale value. A well-maintained interior and exterior adds about $1,500 to the value of a used car, according to Kelley Blue Book. So when winter is over, the expense of getting a car's carpet steam-cleaned is probably worth it.

So how does Pirotte keep her black SUV gleaming during the cold months? Like other clean-car enthusiasts, Pirotte has a game plan:

After it snows, she heads to a professional car wash between 10:30 and 11 a.m. or mid-afternoon on a work day to avoid long lines of dirty cars. If lines are long anyway, she heads to a self-service car wash.

Her favorite accepts credit cards, unlike many self-service places that require quarters or crisp dollar bills for the change machine. She uses a pre-wash rinse, then the power wash, spraying one section at a time from top to bottom.

To dry the car, she uses the giant dryer at the car wash. She carries an old towel with her to wipe up the spots the dryer didn't reach.

She uses disposable wipes to make her grimy gray tires black again. She spends about five minutes on the task. "It makes a huge difference," she says.