Mark Day (born September 21, 1961 in Clarksville, Tennessee) is a former NASCAR driver, racing for a number of years in NASCAR's higher division. In addition, his family currently owns the #05 31-W Racing Chevy in the Busch Series. That team races in that series on a part-time basis and full-time in the ARCA RE/MAX Series.

Day only made one career CTS start. It came at Nashville Speedway USA in the #50 R & Z Motorsports truck. He started 23rd, but only managed 31st in the thirty-four car field. This is after he had mechanical woes.

Day made his debut in 1997, running five races for his family's 31-W Insulation team. He made his debut in the inaugural race at Texas, starting 37th. A mid-race wreck claimed his car and gave him a finish of 36th. It did not get much better for Day. He best finish on the year would end up being 31st at Talladega and had only a best start of 36th at Bristol. Simply put, it was not Day's dream season.

Day would scale down to one race for 1998 and for the rest of the years of his career, for that matter. He started 40th and finished 36th at Pikes Peak. He only competed fifty laps due to engine failure.

Day's one start in 1999 turned out to be just as poor. After starting 34th in the August Bristol race, Day managed 41st after a crash early in the event.

Another crash sideline Day in his 2000 start. He started 24th at Nashville, and this would turn out to be his best career start. He only finished 40th, however, due to a major late-race crash.

Day closed out his Busch career in 2001, finishing it with two consecutive starts. He did not finish either, but ironically, Day had his best career finish in that. After a 36th finish at Texas, Day was crashed out early of the inaugural event at Nashville Superspeedway. However, it turned up to be a 31st-place finish and his best career showing.

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