I have noticed some things that I can't understand in the Back To The Future films about the DeLorean.

In part I, when Einstein is sent 1 minute into the future the DeLorean comes back completely frozen. Why wasn't it cold in any of the other times when it was used for time travel?

In part III, the fuel line goes and this prevents it from going up to 88mph which they use a train to get up to 88mph instead. Since the DeLorean was turned into a flying car in part II, why didn't they just have it fly instead of using a train to get it to 88mph?

  • 16
    Didn't the lightning strike which sent DeLorean back to 19th century damage the flying capability as well? Commented Feb 23, 2013 at 8:25
  • 1
    I can't say for sure as I don't have the movie to hand but doesn't Doc Brown make a comment about the ice on the car? Something to the effect of 'energy transference' or some other pseudo-scientific mumbo jumbo?
    – user11295
    Commented Feb 23, 2013 at 9:01
  • @DVK Yes. It is stated in the letter Doc. Brown sends to Marty (and subsequently narrates to him in his younger form after Marty returns to his 1950s Hill Valley residence). Marty has to explain to the younger Doc. Brown that the older version had a hover conversion done. Commented Feb 23, 2013 at 12:02
  • @DVK That's incorrect.. DeLorean was out of gasoline actually. Waste materials could only be used to power Time Circuits..
    – user931
    Commented Feb 23, 2013 at 14:27
  • 4
    Not an in-movie answer, but from the DVD commentary, the real world explanation is that while the production team liked the effect, it just became an enormous hassle to ice down the car with liquid nitrogen for every take. Apparently by the time they got it iced and got everyone in place for the shot, it was almost melted again.
    – Mike Clark
    Commented Aug 13, 2013 at 13:53

5 Answers 5


The formation of ice requires at least 3 things.

  1. Cold
  2. (The normal, linear passage of) Time
  3. Moisture

The time factor is clearly seen in both Einstein's short trip and Marty's trip from 1955 back to 1985 at the end of the movie.

Here is the return of the DeLorean with Einstein just as the car is spinning to a halt.

Einstein's return - 1 - No Ice

But here it is a few moments later.

Einstein's return - 2 - Ice

Here is the car just moments after it has crashed on return from 1955 to 1985. Some mist, but not much ice, if any.

Marty's return from 1955 to 1985 - 1

And by the time the terrorists are coming to get revenge on the Doc., ice is apparent.

Marty's return from 1955 to 1985 - 2

So the Doc. mentioned cold, we've seen the effects of time, the other factor is moisture, or in this case, humidity.

The scenes where Marty goes from 1985 to 1955 are slightly different, in that the car is surrounded by mist, but there is little evidence of ice on it while in the barn. By the time Marty drives it back out of the barn, the effect has vanished.

Here is the first part of the time in the barn, the mist is obvious but there is not much ice, if any.

Marty's trip from 1985 to 1955 - 1 Mist

A few moments later we see that the mist has cleared, and though there is no ice on the car, there is a sheen of moisture on the bonnet and windscreen.

Marty's trip from 1985 to 1955 - 2 Sheen

My conclusion is that in this trip, it was a lot less humid (to gain less ice), & significantly warmer, to melt it faster.

I was going to review the other movies, but I think this explanation covers why the ice might vary according to the trip.

DVK covered the other question, the flying circuits were destroyed by the bolt of lightning that hit the car at the end of Back to the Future 2. Here is the relevant part of the letter read near the start of BttF 3:

Doc. Brown: The lightning bolt that hit the DeLorean caused a gigawatt overload which scrambled the time circuits and activated the flux capacitor and sent me back to 1885.

The overload shorted out the time circuits and destroyed the flying circuits. Unfortunately the car will never fly again.

  • 5
    @SachinShekhar I reviewed it again and added the relevant part of the letter. Note that 'circuits' do not use petrol in any case, but electricity. Given the 'Mr Fusion' generator, if the time circuits were repairable and the flying circuits had not been destroyed, he could have powered them both using the fusion generator and escaped back to 1985. When you have an electrically powered flying capability and great gobs of electrical power, petroleum is irrelevant. Commented Feb 23, 2013 at 14:50
  • 1
    That makes sense now. Thanks! Commented Feb 23, 2013 at 19:20
  • Its possible that time circuits consume full power output of Mr. Fusion, otherwise there was never a need to install gasoline based system. The whole car could be electrical.
    – user931
    Commented Feb 24, 2013 at 2:55
  • 1
    @SachinShekhar "..time circuits consume full power output" Possible yes, but highly improbable. But even if they did, it would be trivial to take a flying car to several kilometers/miles altitude, switch off the flying circuits, drop to 88 MPH to do the time jump & ..switch the flying circuits back on after the jump. Note that power (e.g. gigawatts) is not equal to energy (gigawatt hours). Power is a flow rate of energy. BTW - though I thought your answer was quite low quality (especially the first part re the ice), I did not down-vote it (in case you are wondering). Commented Feb 24, 2013 at 3:47
  • 1
    "The flying system wouldn't be designed to take power from Mr. Fusion" So what? Changing a cable from the engine to Mr Fusion would be trivial. Commented Feb 24, 2013 at 13:40

The out-of-universe reason for the disappearing ice was explained in the commentary track to the first movie (transcript here) with writer Bob Gale and producer Neil Canton, and Gale also suggested the in-universe reason could have something to do with the switch from the plutonium power generator to Mr. Fusion:

Bob Gale: I believe this was liquid nitrogen that we had sprayed all over the car to ice it up.

Neil Canton: It was also a problem keeping it on the car... it would drip off several times before we were ready to go.

Bob Gale: This is the iciest you'll ever see the DeLorean. You'll notice as the movie goes on, when the DeLorean reappears from a time trip, there's less and less ice on it, and finally by the time we're into the sequels there basically isn't any. I figured we used Mr. Fusion as an excuse why we weren't gonna have ice on the car anymore - great idea, great visual, and a pain in the ass to shoot.

The other part of the question is covered in Andrew Thompson's answer, with the quote from Doc's letter saying the lightning "destroyed the flying circuits".


As much as every one of us would like to justify the lack of ice formation on the car... apart from the first time travel trip it was never brought up in conversation or shown. The first time the car gets so cold doc can't even touch it. that much ice just forming out humidity in air means the car was very very cold. Later time travels the car doesn't ever freeze over untouchably like that. it looks like it was a wow-factor added in the first scene and because it didn't have relevance to the story they ignored it later on.

  • I could be wrong, but I think the first trip in the mall parking lot might be the only time we see someone actually attempt to touch the outer surface of the DeLorean within the first few seconds of its arrival. In the 1955 barn Marty sits in the car regaining his bearings for a moment; upon returning to 1985, he rushes to the Doc... Einstein's trip is also immediately followed by a brake-locking stop. So we can probably infer that all the other trips gave the car enough time (30 seconds?) to warm up again. Commented Oct 20, 2015 at 19:55
  • Sure, but that iced look is never repeated.
    – Gomes
    Commented Oct 25, 2015 at 4:46
  • I disagree I'm currently watching bttf 2 and there is ice when they go back from 1985 to 1955. I don't understand why they didn't notice the ice when Biff travelled from 1955 to 2015. I guess there are some logical mistakes, but it's ok, the films are still great.
    – faysou
    Commented Dec 10, 2023 at 17:03

Hoverconversion circuits. As in computer circuits. Unavailable even in 1955. Time travel circuits may be repairable in 1955 (hence the primitive vacuum tubes patched together by 1955 doc when the DeLorean jumps in the drive-in parking lot and brings them to the old west) but antigravity circuits would have taken technology that harnesses the fourth fundamental force unavailable to all versions of doc browns regardless of propulsion method.

  • Welcome to SciFi.SE! I'm afraid I don't quite understand how this is supposed to answer the question. First of all, what do "hoverconversion circuits" and "antigravity circuits" have to do with the DeLorean not always being covered in ice? Second of all, what's your source for this information?
    – F1Krazy
    Commented Jan 7, 2020 at 13:59
  • 1
    @F1Krazy I believe this is answering the "why didn't it fly in 1885?" part of the question; this seems to imply the flying capability was damaged and not repairable in that time.
    – DavidW
    Commented Jan 7, 2020 at 14:02
  • @DavidW I didn't realise the question was actually asking two different questions.
    – F1Krazy
    Commented Jan 7, 2020 at 14:03

First part of your question:

Why wasn't it cold in any of the other times when it was used for time travel?

A Plot Hole.

Second part of your question:

Since the DeLorean was turned into a flying car in part 2, why didn't they just have it fly instead of using a train to get it to 88mph?

From Wikipedia article of Back to the future Part III (Plot section):

Marty arrives on September 2, 1885, in the middle of a United States Cavalry pursuit of Indians. While evading the pursuit, the DeLorean's fuel line is torn, forcing Marty to hide the car in a cave and walk to Hill Valley.


Doc agrees to leave 1885, but with the DeLorean out of gasoline and no more available, there is no way to accelerate the car to 88 miles per hour.

Waste materials could only be used to power Time Circuits. Flying required gasoline.

  • 2
    "Doc agrees to leave 1885, but with the DeLorean out of gasoline and no more available, there is no way to accelerate the car to 88 miles per hour." The flying circuits used electrical power! See the edit at the end of my answer and subsequent comment in same answer. Commented Feb 23, 2013 at 14:53
  • It's not clear that those were electrical circuits or not. Even if they were electrical, then what? Gasoline might have required to produce enormous amount of electrical power (future engine) which you couldn't create outside in 1885.
    – user931
    Commented Feb 24, 2013 at 3:03
  • 1
    "It's not clear that those were electrical circuits or not.: Well they sure aren't a 'County Court Circuit'. "Gasoline might have required to produce enormous amount of electrical power (future engine)" Running on 'future gasoline'? Even if you combusted the entire fuel load in a single instant with 100% efficiency, it would not provide so much as 1% of the '2.21 gigawatts' required by the time flux capacitor (hence we can presume Mr Fusion is able to provide at least that much power). I feel you are clutching at straws. Commented Feb 24, 2013 at 3:20
  • 1
    The Mr. Fusion was to replace the original Plutonium reactor that fueled the time circuits originally. The flying capability was referred to as a "Hover Conversion", it was still powered by the internal combustion engine of the Delorean.
    – Monty129
    Commented Feb 24, 2013 at 18:11
  • 1
    When the DeLorean was struck by lighting in Part 2 it damaged the flying circuits, 1885 Doc Brown says this in his letter which the current Doc Brown reads aloud and is astonished that it could fly. as such it couldn't fly when it first went back to 1885, it was never repaired before Marty received the letter as to where it was left and it was never repaired before it's second trip back to 1885 because the parts to repair it never became available. as such a torn fuel line had nothing to do with the flying capabilities
    – Memor-X
    Commented Jul 14, 2014 at 5:03

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.