If your chills are multiplying—well, for starters, maybe turn down the AC a notch.

But remembering that Grease came out 45 years ago could also be the culprit, in which case the only prescription is to tell you more about the enduring classic. The result should be a pleasant nostalgic glow, warm as a summer night, though side effects may include hopeless devotion and hallucinating that your guardian angel is Frankie Avalon.

In any case, the 1978 musical was an automatic, systematic and quite possibly hydromatic classic upon arrival and became the top-grossing movie of the year, burnin' up the box office to the tune of $160 million.

John Travolta told E! News in 2018 at a celebration for the film's 40th anniversary that the memory that stood out to him from that time was "meeting Olivia, beyond a shadow of a doubt." Olivia Newton-John, standing beside him, added, "John came to talk me into doing it, and that was a magical, magical day."

At 29 and 23 in Grease, respectively, Newton-John and Travolta weren't exactly the teen sweethearts they were playing (Rydell High was obviously full of adults, part of the film's kitschy charm), but their chemistry as good girl Sandy Olsson and bad boy with a heart Danny Zuko was certainly key to the film's success.

And there are worse things you could do than read on for more secrets about Grease:

The fated pairing of John Travolta and Olivia Newton-John wasn't always a given when it came to casting the roles originated on Broadway in 1972 by Barry Bostwick and Carole Demas.

Linda Ronstadt and Marie Osmond were among the names suggested to play Sandy, Travolta recalled to Entertainment Tonight, "and I said, 'They're wonderful, but every guy in the world wants Olivia Newton-John as their girlfriend.' And I knew that 'cause I felt the same way...And I said, 'If you don't see this, you guys are nuts.'"

Carrie Fisher, Bye Bye Birdie star Ann-Margret and The Partridge Family's Susan Dey were also on the list of possible Sandys.

When producer Allan Carr raised the idea of Newton-John, she didn't immediately say yes. (But when she did, Sandy was rewritten to be Australian.)

"I was very anxious about making another film, because my music career was going well," the "Physical" singer recalled to Vanity Fair in 2016, "and I did not want to mess it up by doing another movie that wasn't good."

Henry Winkler called himself a "damn fool" for turning down the role of Danny Zuko—though his reasoning in the 1970s was that he was already playing a slickly coiffed, leather jacket-wearing cool cat as the Fonz on Happy Days and didn't want to be typecast.

"I go home...and I have a Diet Coke," the Barry star told CNN's Chris Wallace in November 2022. "John Travolta, who has done the movie, goes home and buys a plane."

Travolta had already made Saturday Night Fever when he scored the role of Danny, but it wasn't released until December 1977.

So he wasn't yet a major movie star when they shot Grease in the summer of 1977, though by the time it came out on June 16, 1978, he was—and Oscar-nominated to boot.

But the life-changing projects were essential for Travolta in another way: His girlfriend Diana Hyland had died of cancer on March 27, 1977, and being busy helped.

"It acted as a giant distraction for me," Travolta told Vanity Fair. "It was probably the healthiest thing I could have done was to be in back-to-back movies, because I was very sad."

Frankie Valli sang the title track, but it was written by his fellow falsetto master Barry Gibb—while the Saturday Night Fever soundtrack, anchored by the disco sounds of the Bee Gees, was still in the midst of a 24-week run at No. 1 on the album charts.

The two films shared a producer, Robert Stigwood, who was also the Bee Gees' manager and brought Gibb in at the last minute to replace a song that had already been written.

Director Randal Kleiser was admittedly concerned about starting the whole movie off with a tune that didn't have a 1950s vibe, but "Grease" spent two weeks in the top spot on the Billboard Hot 100 singles chart and was nominated for a Golden Globe, as was "You're the One That I Want." (They lost to Donna Summer's "Last Dance" from Thank God It's Friday.)

"Hopelessly Devoted to You" was the only Grease tune written for the movie (by John Farrar) that ended up nominated for a Best Original Song Oscar (again losing to "Last Dance")—and it was the film's only nomination.

Though Travolta and Newton-John went together like rama-lama-lama-ka-dinga-da-dinga-dong, the original Grease musical saw some intriguing stars come and go.

For starters, the film's Kenickie, Jeff Conaway, had a run on Broadway as Danny, and Travolta played T-Bird member Doody in a touring production.

Other Broadway Dannys in the 1970s included Peter Gallagher, Patrick Swayze and Treat Williams, while Richard Gere starred in the original West End production in 1973.

Grease originally took place in Chicago, where Jim Jacobs and Warren Casey wrote and first staged the musical, but the movie version was set in Los Angeles.

Venice High School (bleachers and other exterior campus shots), John Marshall High in Los Feliz (graduation carnival) and Huntington Park High (the gym dance) stood in for Rydell High, and the iconic drag race scene was shot in the L.A. River Basin between the 1st Street Bridge and 6th Street Viaduct.

Those bridges are familiar from dozens of movies, including The Naked Gun, Terminator 2: Judgment Day and Furious 7.

Stockard Channing, who beat out Lucille Ball's daughter Lucie Arnaz for the role of Rizzo, was the eldest of the so-called teen cast at 33.

"I would get up close to them and see if they had any crow's-feet around their eyes and that would show they were beyond the surreal age that we had determined would work," Kleiser, who had previously directed Travolta in the 1976 TV movie The Boy in the Plastic Bubble and was the actor's personal pick to make Grease, told Vanity Fair in 2016. "High-school kids could not have crow's feet."

In Grease: The Director's Notebook, Kleiser detailed how cinematographer Bill Butler used soft lighting on 29-year-old Newton-John to erase any lines on her face—"not that Olivia had many," he noted.

It got so hot in the gym where they spent five days shooting the school dance—without air conditioning and unable to leave the windows open due to the stench from the meatpacking plant next door—that Michael Tucci (T-Bird member and "so-called mooner" Sonny) fainted and was rushed to the ER.

Rumor has it Elvis Presley passed on playing Teen Angel, the role that went to Frankie Avalon—who was so afraid of heights the crew put mattresses on either side of the staircase he descended while crooning "Beauty School Dropout," just in case.

Presley died Aug. 16, 1977, at Graceland while they were still filming Grease in L.A.

In the stage version, "Grease Lightning" is Kenickie's song—but Travolta was able to swing it so he could sing it instead.

"I have to be completely honest with you," the actor told Vanity Fair. "I wanted the number. And because I had clout, I could get the number."

Conaway, who died of pneumonia exacerbated by chronic drug abuse in 2011, wasn't particularly happy about it and neither was choreographer Patricia Birch.

"It's Kenickie's goddamned number!" she told the magazine. "I was upset with it, because I thought Jeff needed a number. John was very good doing it, but it should have been Kenickie—it was Kenickie's car!"

Steven Ford, the youngest son and third child of former President Gerald Ford, was originally cast as jock Tom but got a case of cold feet and dropped out—even though the character literally only needed to look handsome and mouth "Hi" and "How are you?"

The production quickly cast 19-year-old Lorenzo Lamas as Sandy's boyfriend-for-a-minute whose "brains are in his biceps." He had to dye his dark hair blond so he would contrast more with Danny. But, Lamas recalled to Vanity Fair, "I would have dyed it purple to be in that movie."

Ellen Travolta—perhaps best known for playing Scott Baio's mom on Charles in Charge—is John's older sister by 15 years (he's the youngest of five). 

You can see her among the waitresses gathered around the TV at The Frosty Palace, the diner hangout that was recently reconstructed for the Paramount+ prequel series Grease: Rise of the Pink Ladies.

Newton-John was unrecognizable when she first walked out in her "goodbye to Sandra Dee" teased curls, skintight leggings and leather jacket (which the actress, who passed away in 2022, continued to wear to Grease press events decades later). 

Didi Conn, who played beauty school dropout Frenchie, recalled to ET that her Australian co-star first tried on the bad-girl look at night when they were on set shooting the drive-in scene, and nobody realized who she was.

"It was a natural reaction," Travolta told ET about Danny being brought to his knees by his first glimpse at Sandy's makeover. "It was so much fun to see her dressed up in that garb."

The 1982 sequel Grease 2, starring Michelle Pfeiffer and Maxwell Caulfield, has its fierce defenders, but it isn't widely, shall we say...beloved.

Alas, producer Carr's original idea for a follow-up—Summer School, which would have seen the T-Birds and Pink Ladies reunite for Rizzo and Kenickie's wedding—was not the one that got made.