Putting rejected clunkers back on the road.

This weekend marks the new model year for the people who buy cars we donate to charity.

The cash-for-clunkers program in Washington on Friday changed some of the models that qualify for the federally-created trade-in plan. The feds are scratching 78 models off the list for which they'll pay as much as $4,500 and adding 86 others in their stead.

Officials at www.cars.gov also tweaked guidelines for consumers' rights and dealers' obligations under the program to keep things humming while dealers worry about how soon they'll be repaid for money they fronted to buyers.

Charities who previously relied on donated clunkers have been worried the last couple weeks that those contributions might nosedive because drivers will trade their aging bolt-buckets into the government program instead. Some low-income Californians even called a protest to call attention to harm they expect to suffer as a result.

Some donations have fallen off, but the Associated Press reports that other charities find some contributions are increasing because people are turning in vehicles that the CARS program rejects. More than 150 agencies, including at least three in the Kansas City area, count on clunkers to help low income families find affordable cars for getting to work and basic needs, says Opportunity Cars, a national clearing house for such groups.

Drivers looking for cash-for-clunkers trade-in money also need to watch out for a widening variety of scams involving the program, warn the Federal Trade Commission and the Better Business Bureau.

As always, do the math before you commit to any cash-for-clunkers deal and crank your changed insurance, tax and other costs into the equation. It's your best defense against disappointment at best or a ripoff at worst.