Mechanical inclinations have, for various reasons, traditionally been forte of men. The Wrench Wench is a girl who sets out to change all that. This can sometimes extend to pure electronic devices, but a Wrench Wench is more likely to be found with a blowtorch and ratchet set. She will always be confident about her own work, but because she's technically an enormous geek she sometimes has trouble with other things. She might also have Machine Empathy and can diagnose problems just by listening to the motor. She has been known to be Curious as a Monkey in the presence of new and interesting machines — or Constantly Curious, if inspection is impossible.
Usually too self confident to ever need a Beautiful All Along plot, but very likely to have at least one She Cleans Up Nicely moment even though she's often an Unkempt Beauty anyway.
Can be used as a contrast to show that she's not as feminine as she first appears. She's often a Ms Fix It. Can also be The Blacksmith. When a Wrench Wench's talents go above and beyond the practical or realistic, she's also a Gadgeteer Genius. If it's computers and the Internet instead of mechanics, she's a Hackette. If her skills wax more technical than mechanical, chances are she's a Hot Scientist, though overlap can exist when dealing with things like mecha and androids which encompass both elements.
The less objectifying version of Hood Ornament Hottie, where the woman may be dressed or posed as if she was the mechanic, but actually isn't. A subtrope of The Engineer.
Ikuyo in Hanaukyō Maid Tai is the hand maid of the main character's Maid Corps and invents all sorts of inventions for the main character, which unfortunately have a tendency to explode or malfunction.
Miyuki Kobayakawa of You're Under Arrest! practically built her mini patrol car from the ground up, and maintains Natsumi's motorcycles.
Leyte in Tengen Toppa Gurren Lagann is the chief mechanic for team Dai-Gurren and is responsible for the majority of the upgrades to the mechs and the battleship.
Kana in Haibane Renmei is a tomboy who works in a clocktower and loves to work on machines.
Fio from Porco Rosso - who turns out to be the heiress of four generations of female aircraft builders. (Her great-grandmother wields a mean tinsmithing hammer.) The entire workforce of Piccolo Aviation are women, since the men are all abroad looking for work.
Rally Vincent in Gunsmith Catsis a gunsmith after all, and she's shown teaching May in the manga. She's never shown working on her own cars though, though she does wank over its capabilities at times.
Charlotte E. Yeager from Strike Witches. Before joining the witches she worked on motorcycles and airplanes, consequentially her striker unit is heavily modified. Even after joining the witches she spends her spare time in the machine shop and making further modifications to her striker unit.
Nae Aki in Medarot Spirits; she never was anything near fanservicey, but, in another hand, had Ikki slightly fawning over her. Justified by the fact that she's the granddaughter of Dr. Aki, the modern Medarot inventor. Thing is, if you considers the series' existence at all.
Hilde Schbeiker from Gundam Wing, who has her own scrapyard and is quite proficient with computers.
Bulma from Dragon Ball is this. She's handy with gadgets, and, along with her father, is usually responsible for creating spaceships, as well as Trunks' time machine.
Rikako Ota from Wangan Midnight, the daughter of RGO shop owner Kazuo Ota. She could dismantle and rebuilt a whole engine by herself down to the crankshaft, and is in fact slated to inherit her father's shop..
Miki Jounouchi from Future GPX Cyber Formula is a tomboy and chief mechanic for her racing team. She once takes out the damaged turbine engine from Super Asurada AKF-11 while it is still hot and injures her hands for doing that.
Chinatsu from Jormungand is a villainous example. When she's not gunning people down as part of her hitman duties, she apparently likes to build complex mechanical torture devices... including one designed to shoot a bound captive in the knee. In the same spot. 27 times.
Nanvel Candlestick from Burn Up W/Excess. Quirky but genius inventor and still as busty as most of her squad.
Kay and Hazel, the female leads in Swing Shift, both become wrench wenches after joining a munitions facility during World War II.
As bizarre as it may sound, Disney seems to be taking Tinker Bell, of all characters, in this direction with her CGI movie. The reasoning is actually fairly logical—why else would she be named Tinker Bell? Plus, the novel Peter Pan is based on states that Tinker Bell is a tinker who mends the pots and pans. It's not like Disney pulled this out of nowhere.
Mary in The Muppets is very good at working with cars and electricity.
Jimmy Neutron's mother is seen working under the family car at one point.
She also pointed out a flaw in one of Jimmy's inventions and explains it in full Techno Babble. It turns out she was very right.
The main character of C. E. Murphy's Urban Shaman trilogy is one of these, being a dedicated car enthusiast who restored a 1969 Mustang all by herself, and worked as a mechanic for the Seattle Police Dept. She even continues to use the idea of fixing a car to work her healing magics (fixing a broken windshield, replacing a flat tire, using windshield wipers to clear her vision, etc.).
Nadia Chernyshevski of the Red Mars Trilogy was a nuclear engineer in Siberia before her job building mankind's first base on Mars. Her skills in solving technological problems earned her the nickname "Universal Solvent".
Mercy Thompson, a.k.a. Mercedes the Volkswagen mechanic. She got started at 16 when she was sent to do community service fixing up cars, and now she owns and runs her own garage.
Samella Connel from Douglas Hill's Col Sec Trilogy, although her particular talent seems to be mostly with computer hardware and programming.
Dagny Taggart, the main heroine of Atlas Shrugged, can't live without her railroad, is not too keen on pointless parties that other rich girls go to and has a very masculine dress code.
Linda Connor, from Swedish SF author Anders Blixt's dieselpunk spy adventure Iskriget (The Ice War), is a trained mechanic with a solid professional reputation in her home town. She "saves the day" with her skills at several occasions during the story. She usually wears workmen's clothes and has a male haircut, both for purely practical reasons.
Although Alice has spent most of her life studying sorcery her real gift is with watches and mechanical things, including her creating TheWitch Watch.
As both she and her father are highly ranked engineers, Laeshana from Quest Of The Unaligned has traces of this.
Mac, whose real name is Cindy Mackenzie on Veronica Mars is a computer hacker who helps Veronica with mystery cases.
Kaylee of Firefly and Serenity, as quoted above. Kaylee actually joined the crew because the captain walked in on her having sex with the ship's mechanic in the engine room. She diagnosed the engine's problem while in the act, and fixed it on the spot when Mal showed up. He fired his mechanic and hired her as she was getting dressed.
There are numerous hints (including dialog by the first ship's mechanic) that her major motivation in having sex with him there was to get up close and personal with the ship's engine room and grok it, she being a technophilic homebody / ground-pounder up to that point.
Bester: Engines make her hot, you know?
(Later, after Kaylee fixes the engine in two seconds flat:)
Bester: What'd you do?
Mal: She fixed it! Where'd you learn to do that, miss?
Kaylee: Just do it, is all. My daddy says I got natural talent.
In "Shindig" when Mal and Kaylee go to a ball she cleans up and gets to wear a fancy dress. She becomes an instant hit at the party when many of the men present find out that she works on engines and knows almost anything there is to know about them. Despite the fancy clothes it is still a frontier world and a technical whiz like her is highly respected, and the other female partygoers look to be socialites with little to offer but small talk.
Turns into a CMOF when a young man asks her to dance and everyone else tells him to leave her alone, she's talking about engines!
Gilina Renaez from Farscape is a technical specialist for the private army she works for.
B'Elanna Torres from Star Trek: Voyager. Although Star Trek engine rooms tend to be cleaner than a modern-day operating theatre, she does still manage to get covered in dirt and grease on a fairly regular basis.
Theora Jones of Max Headroom is of the high-tech variety rather than the grease-monkey variety.
Ashley Hammond in the Power Rangers Turbo episode "The Turn of the Wretched Wrench". Conversely, this was the day job of her Japanese counterpart, Natsumi Shinohara from Gekisou Sentai Carranger: she's good enough to dismount a moving bike.
Sanctuary has Dr. Helen Magnus, also played by Amanda Tapping, who again falls under this trope. Very obvious in episode 21, where they get stuck in an old oil rig and need to MacGyver their way out.
While we didn't get to see much of it "on panel," DG from Tin Man seemed happiest either drawing or fixing stuff with her robotic foster dad.
In one episode of Home Improvement, car enthusiast Tim gets a new mechanic who is one of these, which leads to him becoming slightly attracted to her. Of course, the fact that she is Jenny McCarthy doesn't hurt, either.
In Degrassi Goes Hollywood fashion model Mia, who tags along on the journey to L.A., later ends up helping fix the broken down bus with her expensive leggings, saying it was an old trick her mom taught her.
The Audiobooks for The Sarah Jane Adventures make this into Sky's way to assist the team, in a much cuter and less fanservicey way. Her ability to sense and understand energy being part of it, but she just understands machinery.
When the family starts fixing up a car for Matt in season 3 of 7th Heaven, it's boy-crazy Lucy who is shown to be an idiot savant when it comes to cars.
In The Protomen (a rock opera based on the Mega Man series), Dr. Light's lover works in a factory. Keeping her safe from a dangerous job is part of his motivation for creating the robots central to the series. Of course, Dr. Wily has other plans.
The entire first verse from Felt's "Dirty Girl" is about this. Lines include "Standin' there holding that drippin' dipstick/With a firm grip, yet so delicate/And the way you took that orange oil rag and wiped it clean/Its guaranteed to get repeated in my dreams" and "Got so lost in your smile when you asked me what the mileage was"
The Beach Boys' "Car Crazy Cutie" is an ode to a woman who shares her beau's enthusiasm for automobiles:
Well, my steady little doll is a real live beauty
And everybody knows she's a car-crazy cutie
She's hip to everything, man, from customs to rails
And axle grease embedded 'neath her fingernails!
Lucca from Chrono Trigger, a machine enthusiast who takes after her father, is one of the earliest video game examples.
Roll Casket in the Mega Man Legends series who a genius mechanic who's in charge of piloting and maintaining her family's airship .
Also, Tron Bonne combines this with a fancy for designing robots, although generally she tends to design new electronics more often than fix old motors.
Led Campbell from Septerra Core is a genius mechanic, her weapon is literally an enormous wrench, and she's so hot that total strangers will give her money or items..
Tali'Zorah from Mass Effect who's part of an alien race called the Quarians. Quarians are the whole race of incredibly skilled engineers. And even among the quarians, she is counted one of the best engineers and geth specialists.
Like most character tropes involving the squad, Fem Shep can qualify for this one too - just make her an engineer.
They are joined by Samantha Traynor in Mass Effect 3, though she's more the communications officer and spends her time cracking code.
Alyx from Half-Life 2 is a Wrench Wench and an Action Girl combined in one. Not only is she a good mechanic, she's also a godly hacker. Where she learned the latter (even touching a Combine computer is punished by summary execution) is a puzzle.
Keira from the Jak and Daxter trilogy. Tess is one as well, only her specialty is weaponry, not vehicles.
Samanya in Red Faction: Guerrilla is the chief engineer of the Red faction organization and creator of all their weapons.
Eva Navarro of Mercenaries 2: World In Flames. She'll build any number of custom PMC vehicles for you, for a price.
The original Ann from Harvest Moon and her Magical Melody incarnation love to tinker with machines and invent things.
Penelope from Sly Cooper 3; specialises in remote-controlled vehicles, so the gang try to hire her on.
Veronica has a bit of this going on as well. She can even function as a mobile Workbench that lets you craft items on the spot.
Licca Kusunoki in Gods Eater Burst fits this to a tee, in charge of maintaining the Far East Branch's God Arcs. complete with oversized gloves and a tendency to hug the protagonist when they do something stupid.
Wave the Swallow in Sonic Riders, who is the one responsible for building the boards for the Babylon Rogues.
When Starkiller first lays eyes on Juno Eclipse in Star Wars: The Force Unleashed, she is working on his ship, The Rogue Shadow. The comics also show her working on other equipment.
Robin from The Iconoclasts is a mechanic in a world where mechanical engineering is illegal.
Touhou Project gives us Rika in it's 2nd installment, who builds tanks, and is rarely seen without her wrench in fanart.
Kawashiro Nitori from Touhou 10 Mountain of Faith, like most kappa in the series, is a Magitek engineer who dons optical camouflage, extendible robots arms, and missiles. She's really fond of human technology that falls across the Great Hakurei Border and, according to common fanart, has her own lines of electronics.
and is actively working on a spacecraft able to make the journey to Jupiter within her guardian's lifetime.
Borderlands 2 gives us an unusual example, Ellie. Although she is one of the most obese characters in the game, speaking to other characters and listening to audiologs reveals that there are some poeple on Pandora who like it that way.
Pella the dwarf, from Looking for Group. She fashions Rayd a replacement arm after the Black Dwarves dismember him while torturing. Rayd then uses it to "keep a promise" that he made them in a subsequent battle with the Black Dwarves.
Faye from Questionable Content recently entered these waters when she built a mini T-Rex that poops espresso, and was originally going for a two-ton T-rex with Hemi power.
Dora, too, has managed to do similar, but from a more computer nerd end of the spectrum, like fixing Pintsize back together after an unfortunate cake mix incident.
Marigold builds her PCs, has taken over the Pintsize fixing, is a webmaster as her real job, and seems to be rather skilled at all things computer.
Shelly from Wapsi Square worked at a garage earlier in the strip's run.
Katherine Blanco from Survival of the Fittest version three was the best mechanic in her school until she was killed by a hornet's sting on the island.
Sharon from Darwin's Soldiers used to work in the magnetic materials research division at Pelvanida. After she got fired, she worked as an electrician and a mechanic in Southport.
Tex, actually, of Red vs. Blue. She's repaired Sheila at least twice, built a bomb out of spare parts (including some more ... personal items), and even upgraded her own armor while wearing it. Apparently, this was part of her Freelancer training. It tends to be overshadowed by her repeatedly kicking everyones' asses, though.
There are quite a few female gadgeteers, devisers and general scientists in the Whateley Universe, but special mention goes to Loophole, whose power is 'understanding rules'. Any and all rules.
Gretchen Grundler and Ashley Spinelli in Recess. Spinelli was taught by her older brother how to work on cars and helped fix a broken down bus in one episode. "Regular, or ratchet?"
Sari from Transformers Animated, in a way. Pre-upgrade, she's the Allspark's deputized Angel of Phlebotinum, then post-upgrade she shows a real talent for Cyber-diagnostics.
Molly from Oban Star Racers is a competent mechanic. She even figured out the problem with a pod-racer when it had previously stumped a professional.
Cover Girl from G.I. Joe (especially in her Devil's Due comic incarnation). After all, when your primary duty is as a missile tank driver, it pays to know how to keep your fighting vehicle in good condition.
Ahsoka has apparently taken a level of this over the course of the series' sporadic timeline; by the time of the Mortistrilogy of episodes, she's capable of fixing a badly crashed shuttle by herself and modifying it as needed.
Mike Holmes has made a point of supporting women going into construction trades on his shows Holmes On Homes and its sequels. He hired Corin "Pinky" Ames on air after she completed an internship with him, and Kate Campbell and Mike's daughter Sherry are regular members of his crew.
There are self-help bike repair shops in Germany (and possibly other places in Europe) where you have to repair your bike by yourself and only pay for the materials used. They are run by volunteers who help you if you're stuck, and many of these volunteers are girls who do this in their free time.
Ada Lovelace, the first computer programmer. In the first half of the 19th century (she was Lord Byron's daughter). That's right: even before the first computer - she invented algorithms for Charles Babbage's Analytical Engine, which is considered the "ancestor" of modern computers.
Note that her mother directed her education towards maths (and music) since she thought the "poetic tendencies" from a typical woman's education of the day were "dangerous" (which is to say she thought poets were trouble; having married Lord Byron, she was probably right)—a course of action with which Lord Byron totally agreed, since young Ada was excellent at maths. Lovelace was nevertheless as feminine as the age required, marrying a count and giving him three children.
Pornstar Phoenix Marie is a lovely and feminine woman ...who rebuilds classic cars, rides and maintains Harleys and plays soccer and baseball in her spare time.