"Revving Up" is the eighth episode of season two and the twenty-first episode overall of the animated children's series The Magic School Bus. It originally aired on November 26th, 1995.
Mr. Junkett, a vehicle maintenance inspector, isn't pleased when he inspects the bus. So he tells Ms. Frizzle that it is going to the junk yard to be condemned. To prove that it is fine, Ms. Frizzle and the class take him on a drive, in which it eventually breaks down after a ride around the hill. When Ms. Frizzle fails to find the problem with the engine, Mr. Junkett finally condemns the bus. He leaves to get a tow truck, and Ms. Frizzle and the class don bodysuits, shrink, and go inside the bus to follow the gas to the engine and find out the problem. They make it inside the gas tank and wonder how they will get from there to the engine. Ms. Frizzle inflates a duck raft and they row through the gas tank. Little do they know, however, Mr. Junkett is on his way with a tow truck ready to take the bus to the junkyard.
Meanwhile, back inside the bus, Ms. Frizzle tells Liz through the screen monitor that she and the class are moving out of the gas tank and into the fuel line, only to come across a sticky substance. They eventually find out it is peanut butter and from the sandwich Mr. Junkett was eating while inspecting the bus. When they clear the line, the gas begins flowing and Liz turns the key to start the engine, sending the class into the fuel pump and leading them to the carburetor. When the engine still doesn't start, they discover an opening at the top and learn that it takes air for things to burn and the engine needs that and gas to run since it burns gas while running. They then learn that it is Mr. Junkett's peanut butter sandwich covering the opening.
With the tow truck getting closer, the class moves the sandwich (and almost Arnold) off the top of the carburetor, only for the tow truck to attempt to tow the bus. Liz desperately turns the key and the class floats around the air. They (minus Arnold) fall into the valve leading to the cylinder. Liz watches the screen nervously as they head to the cylinder which leads her to hide under the bus.
Meanwhile, outside, Arnold wonders where everybody went but is almost caught while Mr. Junkett examines the bus one last time. The tow truck starts up and tows it away leaving Mr. Junkett behind. He tries to catch up to the tow truck as it drives around the mountain but a car comes out of nowhere. He jumps out of its way but ends up rolling off an edge of a hill and left hanging onto a root.
During the tow to the junkyard, Liz is still hiding under the bus, and Arnold is still out on the engine. He informs his classmates, that the bus is being towed away. Liz is informed by this once she makes it back inside after crawling out from under it. Ms. Frizzles orders her to turn the key, but just as she is about to do so, she collapses from exhaustion.
The tow truck makes it into the junkyard and the bus is prepared to be crushed. It is hoisted in between the car crusher by the crane. Arnold tells his classmates if they don't get out, they will be smashed. Ms Frizzle tells Liz she needs to turn the key. She does so and steps on the gas pedal, which makes the piston move. Keesha smells the gas entering the cylinder. Ms. Frizzle tells the class that what goes down must go up when it comes to engine pistons and that the cylinder is where three ingredients come together in order to get the engine started.
When the bus is about to get crushed, the class learns that the engine burns gas and try to find a way to get it to do so. Dorothy Ann reads in her book that gasoline burns very easily, so one should be careful around it. Wanda then learns that the three ingredients of a running engine are gas, air, and a spark. The class then learns that it was the peanut butter that was keeping the spark plug from running. So Carlos cleans it off (only for the peanut butter to stick to him in the process), and the class goes through the exhaust pipe and the metallic maze known as the muffler.
The class exits the exhaust pipe and return to normal size just in time to notice the huge block suspended from a rope about to crush the bus. Liz starts the engine and it transforms into a hot rod. It drives away right before the block crashes down, with the class taking a ride. They thank Liz for saving it from being crushed and find that Arnold is still out on the engine. Liz activates the screen as he falls into the carburetor, goes through the cylinder, and finally exits the exhaust pipe right before returning to normal size.
The class later saves Mr. Junkett from falling off the edge of the hill with a crane from the bus, which had transformed into a tow truck. Ms. Frizzle transforms it back into its regular appearance and Mr. Junkett apologizes to her and the class. She also states that, "A good engine is worth the price of ignition." The bus then drives Mr. Junkett to his speech afterwards.
Transformations the bus used
- Hot Rod
- Tow Truck
- When Liz was hiding under the bus, her eyes are white instead of yellow.
- Carlos does not say any puns in this episode.
- Phoebe does not say "At my old school..." in this episode.
- Dorothy Ann does not have her book bag in this episode, however, she is seen holding a book in a later scene in the cylinder.
- When the bus was being towed away, the doors could be seen on both sides.
- In a couple scenes Arnold could be spotted even though he was out on the engine telling his classmates what was going on (similar to "For Lunch").
- When the class is heading for the valve that leads to the exhaust system, Phoebe's gloves change from red to yellow.
- In one scene in the carburetor, Ralphie's gloves were red and Phoebe's suit keeps flashing to the color of his.
- When Ralphie is asking where Liz is, his cap is missing.
- When Carlos gets the peanut butter off the spark plug, he has some on his suit but in the next shot, it disappears.
- When Keesha asks "Just how big is this fire going to be?", Phoebe is in Dorothy Ann's suit.
- In some scenes when the class was in the cylinder, the gas and air disappear in between shots.
- The class' suits (except Ms. Frizzle's) are color-coded and do not have the school logo.
- When the suits come down from the bus' ceiling, Tim's is not shown.
- Mr. Junkett puts a "CONDEMNED" banner on the bus but in later scenes, it is gone. It may have fallen off later on.
- When Carlos says "Line's clear, Ms. Frizzle!", his suit is the same color as Ralphie's and Dorothy Ann's gloves are pink.
- If you look carefully at the top of the screen when Arnold hides behind the spark plug, Mr. Junkett is not wearing his cap.
- Ralphie's head is noticeably twitching while brushing himself after the class comes out of the engine.
- When the class falls off their stack and tell Arnold to look out, Ralphie and Tim can be seen falling through the carburetor valve even though it was shut.
- In some scenes before the class goes inside the bus' engine, the hood would be closed or open in some shots.
- In one scene when the cylinder is going down, Ralphie, Tim, and Dorothy Ann are missing.
- In one scene as the class falls through the exhaust pipe, Wanda and Carlos are missing.
- At the end of the episode, Liz is missing when Mr. Junkett gets on the bus.
- It is revealed that Arnold hates the smell of gasoline.
- This episode was one of the few that never got released on VHS, but were released on DVD and streaming services later in the 2000s and 2010s. Previous episodes were "Meets the Rot Squad", "All Dried Up", and "Wet All Over".
- Instead of the usual bus-shaped blinking light on the monitor to show where the class is, a blinking circle is shown due to them being inside the bus' engine.
- This is the last episode to air before Halloween in 1995.
- At the beginning of the episode, an invisible screw and bolt can be seen on the ground in the shot with Liz looking under the bus.
- When Mr. Junkett says that the Bus has acid on the paint (For Lunch), dented fenders, and that the roof looks like it was hit by a meteorite (Gets Lost in Space), he references the episodes in Season 1 in which the Bus was badly damaged.
- When Dorothy Ann wears her suit along with her classmates, her hair turns dishwater blonde.
- This is one of the few times where the Bus had been referred to by its full name, "The Magic School Bus".
- When the kids (sans Arnold) get out of the Bus's exhaust pipe, Ralphie's voice is deeper due to his voice actor hitting puberty.