But sometimes their dealers find common cause.
This summer, the Chevy and Ford dealerships in Ludington, Mich., launched a joint ad campaign. Their message: Buy from a local dealership that gives back to the community.
Chevy dealer Mike Urka, who owns Urka Auto Center, gives credit for the idea to Ford dealer Chris Zeppenfeld of Great Lakes Ford, just down the road.
Zeppenfeld told me he wanted to remind residents they don't need to go to a big city for a great deal. Ludington, population 8,400, is on Lake Michigan, 60 miles north of Muskegon and 90 miles south of Traverse City.
The newspaper ad includes a photo of Urka and Zeppenfeld on the beach, posing with two trucks and the Ludington lighthouse. The text lists more than 70 community organizations they support.
Urka's dealership took a double-barreled hit when Chrysler canceled his Jeep franchise and General Motors took away Cadillac, each of which accounted for about 10 percent of his volume. He's down to Buick and Chevy.
The dealers told me their sales are off more than 30 percent because of the economy. But they say the ads have increased floor traffic. Better yet, other local businesses have voiced support for the buy-local campaign, which means there should be benefits for years to come -- for Ford and Chevy.
You can reach Edward Lapham at firstname.lastname@example.org