My 1998 Ford Taurus LX did this and it was just low on engine coolant. My aunts 2001 Nissan Altima SE sedan did the same thing and it was also low on coolant. I thought that was quite strange for a 2001 car, with 28K miles.

__________________
2004 Toyota Sequoia Limited 4wd
1991 Lincoln Town Car Executive
1991 Cadillac Sedan DeVille
1988 Mercedes 300SEL
1972 Chevrolet Caprice Kingswood Estate 9-passenger wagon
1973 Pontiac Grand Ville
(Prior MB's: 1974 240D, 1985 380SE, 1984 190D, 1993 400SEL)