Mexican overdrive 

Taking an automobile out of gear or shifting into neutral while on a decline in an effort to improve fuel economy.

After cresting the top of the hill, Juan shifted his pick-up into Mexican overdrive.

Mexican overdrive by keefer March 3, 2004

Mexican overdrive 

technique of letting a car roll downhill in neutral or even with the engine off.

Mexican overdrive by Anonymous April 25, 2003

Mexican Overdrive 

Putting a car into neutral going down a long hill because your top gear is not high enough to prevent over-revving or because your injectors do not shut off under deceleration

The racers in the Carrera Panamerica in Mexico discovered their cars would go faster rolling down the long mountain grades in Mexican Overdrive than in gear.

Mexican Overdrive by vactrac November 16, 2010

Mexican Overdrive 

When a driver shifts a vehicle into neutral while going downhill, to make the vehicle go faster than if it were in gear.

Buddy I was goin' down that fuckin' hill there on up the road and I just came bombin' down it in mexican overdrive. Fuck that rig goes fast.

Mexican Overdrive by fuckingiver69 November 15, 2018