"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 October 28th, 1995.
Mr. Junkett, a vehicle maintenance inspector, isn't pleased when he inspects the bus. So he tells Ms. Frizzle that the bus is going to the junk yard to have it condemned. To prove that the bus 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 of the engine, Mr. Junkett finally condemns the bus. He leaves to get a tow truck, and Ms. Frizzle and the class shrink and go inside the bus to follow the gas to the engine find out the problem. They make it inside the gas tank and the class wonder how they will get from there to the engine. Ms. Frizzle inflates a duck raft and the class row through the fuel system. 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 rest of the class are moving out of the fuel tank and into the fuel line, only to come across a sticky substance. They eventually find out it is peanut butter and was from the peanut butter sandwich Mr. Junkett was eating while inspecting the bus' engine. When the class clear the pipe, the gas begins flowing and Liz turns the key to start the engine, sending the class into the fuel pump leading them to the carburetor. When the engine still doesn't start, the class discover an opening overhead and learn that it takes air for things to burn and the engine needs gas and air to run since the running engine burns gas. The class then learn that it was Mr. Junkett's peanut butter sandwich covering the opening.
With the tow truck getting closer, they move 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 everyone inside the engine float around the air. The class (with the exception of Arnold) fall into the valve leading to the cylinder Liz watches the screen nervously as the class heads to the cylinder which leads to her to hide under the bus meanwhile outside, Arnold wonders where everybody went but is almost caught while Mr. Junkett examines the engine one last time. The tow truck starts up and tows the bus away with it leaving Mr. Junkett behind, Mr. Junkett tries to catch up to it as it drives around the mountain but a car comes out of nowhere and he jumps out it's way but ends up rolling off a edge of a hill then left hanging on to a root. During the tow to the junkyard, Liz is still hiding under the bus and Arnold , who is still out on the engine informs the class, that the bus is being towed away and Liz is informed by this once she makes it back inside the bus after crawling from under it Ms. Frizzles orders for Liz to turn the key, just as Liz is about to do so, she collapses due to exhaustion. The tow truck makes it into the junkyard and the bus is prepared to be crushed. It is hoisted by the crane and lands in between the car crusher.Arnold tells the class if they don't get out, they will be smashed Ms Frizzle tells Liz she needs to turn the key, Liz turns the key 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 Ms. Frizzle tells the class the cylinder is where 3 ingredients come together in order to get the engine started. When the bus is about to get crushed, the class then learns that the engine burns gas and have to find a way to get it to burn. 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 learn that it was the peanut butter that was keeping the spark plug from running. So Carlos cleans out the spark plug and the class ends up going through the exhaust pipe and the metallic maze known as "The Muffler" (according to Ms. Frizzle).
The class exit the exhaust pipe and grow into their normal human size just in time to notice the huge block suspended from a rope about to crush the bus. Liz starts the engine and the bus transforms into a hot rod. The bus drives away right before the block crashes down, with the rest of the class taking a ride. They thank Liz for saving the bus from being crushed and find that Arnold in still shrunken in size, Liz activates the screen as he falls inside the carburetor, through the cylinder, and finally exiting the exhaust pipe right before growing back to his normal, human size.
The class later save Mr. Junkett from falling off the edge of the mountain with a crane from the bus transformed into a tow truck. Ms. Frizzle transforms the bus into its regular appearance and Mr. Junkett apologizes to Ms. Frizzle and the class. Ms. Frizzle also states that, "A good engine is worth the price of ignition". The bus then drives to Mr. Junkett's 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.
- This is the first (and only) time Ms. Frizzle gets angry.
- 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 the class 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 hat 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 would disappear in between shots.
- The class' suits are color-coded (except Ms. Frizzle's) and do not have the school logo.
- When the suits come down from the ceiling of the bus, Tim's was not shown.
- Mr. Junkett puts a "CONDEMNED" banner on the bus but in later scenes, it is gone.
- When Carlos says "Lines 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 hat.
- Ralphie's head is noticeably twitching while brushing himself after the class comes out of 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 went inside the bus' engine, the hood would be closed or open in some shots.
- In one scene when the piston was going down, Ralphie, Tim, and Dorothy Ann are missing.
- In one scene as the class falls through the exhaust pipe, Wanda and Carlos are nowhere to be seen.
- At the end of the episode, Liz is nowhere to be seen when Mr. Junkett gets on the bus.
- It is revealed that Arnold hates the smell of gasoline.
- This one of the few episodes that has never been released on VHS. However a DVD was made in 2014.
- Instead of the usual bus-shaped blinking light on the monitor to show where the class is, a blinking circle is shown due to the class being inside the bus' engine.
- This is the last episode to air before Halloween.
- At the beginning of the episode, if you look real carefully, an invisible screw and bolt can be seen on the ground in the shot with Liz looking under the bus.