Indianapolis Colts head coach Jim Caldwell isn't holding anything back for Super Bowl week -- including his wallet -- 'cause dude just dropped a monstrous tip after a coaches dinner in Florida this week.

TMZ has learned Coach Caldwell hit Grille 66 & Bar in Ft. Lauderdale on Tuesday night where he and his crew gorged themselves on stone crabs, shrimp, oysters, and "several" orders of the surf and turf.

A source connected to the situation tells TMZ Caldwell and Co. racked up a $2,500 bill -- but left a $1,000 tip ... that's 40%.

TMZ spoke with restaurant manager Peter Brennen who wouldn't confirm the numbers but did admit he was "very generous."

We called the Colts for comment ... but apparently, they're a little too preoccupied at the moment.