Glossary of Automotive Terms

Click on any letter to find automotive-related entries beginning with that letter.

OCIR
Orange County International Raceway.
Occurrence
Any event that resulted in a loss or damage to the insured or the insured's property.
Octane
The hydrocarbon substance in gasoline that reduces engine knock or pinging, which is a noise caused by premature ignition of fuel in the cylinder combustion chamber. The higher the octane number, the less chance of premature ignition. High octane, which has a rating above 91, is useful only when recommended by the manufacturer.
Odometer
Indicates the number of miles a vehicle has been driven. It is illegal to tamper with the odometer reading.
Odometer Rollback
The illegal practice of rolling a vehicle's odometer back to indicate that it traveled fewer miles than it actually has.
Odometer Rollover
Occurs when the vehicle's mileage exceeds the mechanical limits of the odometer ? usually 99,999 miles. This must be certified by the seller, under the Truth in Mileage Act.
Open-End Lease
Also called a Finance or Equity Lease. The lessee is responsible for the difference between the agreed-upon residual value and the fair market value of the vehicle at the end of the lease, if the vehicle is worth less than anticipated. For example, if the vehicle has a market value of $8,000 at the end of the lease, and the residual value was set at $10,000, then the lessee owes the leasing company the difference of $2,000. The lessee has the right to an independent appraisal of the vehicle, at his or her own expense. The payments for an open-end lease are generally lower than those for a closed-end lease.
Opportunity Cost
The cost of using money one way as opposed to using it in another, more economically advantageous way. For example, the loss of interest experienced as a result of removing money from a savings account to be used as a down payment on a vehicle.
Optional Equipment
Equipment or features that can be added to a particular model which are not part of the standard package. These usually involve additional cost and can be ordered individually or as part of a package.
Over-insurance
When the insurance is more than the risk of peril.
Overdrive
A transmission gear with a ratio below 1:1, which improves fuel economy by reducing engine revolutions per minute at highway speeds. On a five-speed manual transmission, the fourth and fifth gears are overdrive. On a four-speed automatic transmission, the fourth gear is overdrive. When an overdrive gear set is engaged, the output shaft turns at a higher rate than the input shaft, reducing engine revolutions at cruising or highway speeds.
Overhead Cam (OHC)
The camshaft is on top of the cylinder head on overhead-cam engines. Single overhead-cam (SOHC) engines have a single cam above the cylinder head. Dual overhead-cam (DOHC) engines have two cams above the cylinder head. All overhead-cam engines are also overhead-valve (OHV) engines, which means the intake and exhaust valves sit atop the cylinder head.
Oversteer
Occurs when the rear tires lose adhesion under cornering. In motorsports, this is also called loose. Oversteer can lead to a spin if the driver doesn't reduce acceleration. See also Understeer.
Oxygen Sensor
Measures the amount of oxygen in the exhaust.

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