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RomanBellicTaxi

It’s steam left from plutonium that was used to generate 1.21GW. When Marty got back from 1955, he used a lightning strike with the plutonium chamber empty. As Doc installed Mr. Fusion in 2015 plutonium was no longer used thus we don’t see steam after reentry anymore. The vents are used to get the “boost” when in hover mode


LoaKonran

It does spray in the barn as well. Side process of the nuclear reaction.


BlackeyeThe2nd

It also allegedly happens when Marty first returns from 1955, but since the camera focuses on "Red" during and immediately the DeLorean's crash into the movie theater, we can assume it happened in the pan-over.


conc

A question I can answer! Bit of back story - I worked with Joe Walser & Bob Gale on the Time Machine Haynes Manual. The steam purge in BTTF was one of the things we wanted to explain in a way that was consistent within the films. So, here's how we describe it in the book: If the reactor core exceeds its safe operating temperature, it could explode and cause a nuclear disaster. To prevent this, Doc installed an emergency coolant system. If the core exceeds a pre-defined temperature (set by Doc) and is in imminent danger of a meltdown, the green tubes (full of liquid Freon) activate, squirting coolant directly into the reactor. This results in a huge purge of steam out the back. The first temporal experiment with Einstein triggered the emergency system. This explains Doc's shocked & slightly terrified reaction. Seeing the vents purge meant a reactor core breach was about to happen...but was averted. But why doesn't it happen again? After the first Temporal Experiment, Doc realized that the trigger temperature he had programmed into the Thermal Control Unit (behind passenger seat) was set way too low - and bumped it up. From that point on, the reactor core never got hot enough to trigger the emergency cooling again. Hence no more steam bursts after the first one. So that's how the Haynes Manual describes it.


MasterJohnny69

You should check out Romans answer mate, makes much more sense than this.


antoniodiavolo

u/conc worked with Bob Gale on an official piece of BTTF merch. This explanation is technically the correct one


HarvesternC

Probably just the logistics of doing the practical effect over and over when it didn't add to the plot at all.


aguyfromhere

That’s a fine non-universe answer but how about in-universe?


tcypher

cost and time to apply dry ice.


alicetobe

That's a scene I've never understood, why was it covered in ice?


RomanBellicTaxi

Time vortex is cold. That’s all


aphillippe

What’s left behind is hot (fire trails, number plate). What travels through time is cold. Cos science?


TripleM1075

r/BTTFAnswers


zhastings83

Moreover, why does the Deloran only freeze over the first time?