Continuity mistake: When Doc's about to send Marty back to 1885 from 1955, and Marty's dressed up...when Doc's walking back and forth loading up the car - look at the shadow from the building. You see it changes by several feet in a few seconds as the scene was obviously shot throughout the day. (00:16:35)
Continuity mistake: When Mad Dog is hanging Marty outside the new courthouse, Doc takes aim stood in bright sunlight (when the camera is behind him), but immediately after shooting him down we see Doc from the front, stood in a large shadow. (00:33:48)
Continuity mistake: When Doc and Marty first see each other in 1885, just before they hug, Doc puts his hand on Marty's shoulder, in the next shot it's on his arm. (00:35:15)
Revealing mistake: During the sequence with the Native Americans chasing the Delorean in the beginning, in one shot looking up at the sky you can see contrails from a plane, obviously not around in 1885. (00:19:25)
Visible crew/equipment: In the scene where Marty is chased out of the saloon in 1885 by Buford "Mad Dog" Tannen & his gang, in the shot showing Marty pushing his way between two women, the cameraman can be seen running along with the camera beside him to the left of the screen. (00:32:26)
Factual error: When the red Presto-log is burning, rivets begin to blow out of the locomotive, supposedly from the pressure. The rivets in the boiler, which would be subjected to pressure, are not visible on the outside of a locomotive. The rivets which are seen to blow out in the movie are in the smokebox, an area which is subjected to heat and smoke, but no steam pressure. (01:40:10)
Visible crew/equipment: When Marty is with Jennifer in his new truck, as the camera cranes down to where they're talking, you can see a crewmember with a white shirt and some of the camera and crane. (01:46:10)
Plot hole: Although Marty rips the fuel line, not all the fuel would have drained out of the tank. Only the fuel that was already in the fuel line would have leaked out, meaning it could simply be patched, bled and the engine would run without a problem.
Suggested correction: A cut fuel line could absolutely drain the tank. Even if not a direct route with respect to gravity, it could still create a siphon effect and drain the tank.
Continuity mistake: At the very end Doc comes back to 1985 in the train. When the train is slowing down they cut to Marty and Jennifer on the ground and the shadow of the train is not moving. But when they go back to the train it is still slowing down. (01:48:55)
Revealing mistake: At the end when Needles tries to race Marty, Marty goes backwards and does a reverse 180. When they show the whole truck right when it's turning, you can see the tracks from the previous takes and the dust that helped the truck spin. (01:47:30)
Continuity mistake: Doc comes back from the past. Jennifer walks to stands next to him. In the following shot, she is still approaching Doc to give him the paper from 2015. (01:50:05)
Factual error: Each time one of the special Presto-logs begins to burn the locomotive suddenly accelerates. In real life the logs would heat the water faster and generate more steam, but there would be an appreciable time-lag between the time the logs begin to burn and the engine accelerates. Also, train engines must accelerate slowly. If too much power is applied the drive wheels merely spin on the rails. (01:35:20)
Factual error: In 1885, Hill Valley and its surrounding areas are shown as having a desert climate, when in both 1955 and 1985, the climate is grassland. In reality, Nevada County, California (where Hill Valley is supposed to be located) is and always has been grassland and forests, not arid desert.
Suggested correction: Hill Valley is in Hill County, as stated at the activation of the clock in 1885.
Revealing mistake: At the very end of this film, Doc appears in his locomotive time machine. In every shot the plate which says 'ELB' changes color. From red to orange. You would say this is a change in light angle, but when the locomotive rises and turns, you can see every angle of this plate and in every angle this plate is red. (01:48:55)
Other mistake: When the movie ends and Doc says, "It means your future hasn't been written yet," watch his son Verne behind. He looks towards the camera and seems unhappy, makes a beckoning gesture (presumably at the crew), and points at his crotch. Seemingly, the kid was having a hard time trying not to pee on himself. (01:50:39)
Continuity mistake: When Marty arrives in 1885 and runs into the Indians, he comes to a slow rolling stop. But the digital speedometer on the dashboard shows that he is still traveling about 70 miles per hour. (00:18:55)
Revealing mistake: In the overhead shot of the train explosion, you can tell which explosion is 'real' and which one is fake - the second explosion appears out of nowhere from the first one. (01:42:00)
Continuity mistake: While at the dance Marty is showing off at the shooting gallery. After shooting all the targets he twirls the gun and hands it back to the booth operator with the barrel in his left hand. Very the next frame shows the gun in his right hand. (00:54:28)
Continuity mistake: When Marty is inside the cave (where he hides the DeLorean), keep a close eye on the huge landscape and very large mountains behind Marty when he is screaming at the bear. The entire background changes when he runs out of the cave to just a few hundred yards of ground before it drops down, where Marty falls into the fence. What happened to the vast landscape and mountains? (00:20:30)
Audio problem: When the very first song ends during the Festival scene, keep an eye on the guitarist to the right. His hand is still moving but no sound is coming out of his guitar. (00:56:55)
