Automotive Glossary


Automotive Glossary

Browse the glossary using this index

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O

O Rings

Circular rubber rings used to seal pipe and other connections.

O2

Oxygen

O2 Sensor

Oxygen sensor, lambda EGO or HEGO sensor to provide exhaust oxygen content signal to the ECM.

O2S

Oxygen Sensor

OBD

On board diagnostic. A connector for diagnostic analysis of a vehicle's electronic systems.

OBD I

Onboard Diagnostics One

OBD II

Onboard Diagnostics Two

Objective

The goal intended to be attained and which is believed to be attainable.

Objective Information

Information that is unbiased and open minded.

Obligatory

Compulsory.

Obscene

Offensive, foul, disgusting.

OC

Oxidation Catalyst.

Occupation

The job that you do. For example, training to be a motor mechanic is training for an occupation.

Octane Rating

The anti-knock property of petrol fuel. The octane rating or number is a comparison against two standard fuels, heptane and iso-octane having values of zero and 100 respectively. Most road vehicles use petrol with octane ratings between 93 and 98.

OD

Outside Diameter

Odometer

Instrument that displays distance travelled by vehicle.

OE

Original Equipment

OEM

Original Equipment Manufacturer.

Offensive

To attack somebody/something.

Office Applications

A package of programs including Word Processor (Word), Spreadsheet (Excel), Presentation (PowerPoint), Email and Organisation (Outlook).

Offset

Any point that is not on the axis of shaft or component.

OHC

Overhead cam - type of valve operating gear. Camshaft in cylinder head above the valves.

Ohm

Electrical unit of resistance.

Ohm's Law

The electrical law, named after its originator, that shows the relationship between electrical pressure in volts, electrical current in amps and the electrical resistance in Ohms is proportional. Volts is equal to amps multiplied by Ohms.

Ohmmeter

A meter for measuring Ohms, the standard unit for electrical resistance.

OHV

Overhead valve - type of valve operating gear. Camshaft in cylinder block connected to valves by push rods and rockers.

Oil Cooler

A small heat exchanged (radiator), which has oil pumped through so that a flow of air will cool it.

Oil Dilution

The thinning of engine oil by fuel flowing down the cylinder walls into the oil pan.

Oil Drillings

Holes through various engine components, such as the crank, to allow oil to flow.

Oil Pan

Sump that holds oil for lubricating the engine.

Oil Pump

An mechanically driven pump used to supply oil pressure.

Oil Seal

A seal that prevents oil loss. Usually described as a radial lip seal but other types are used.

Oil Separator

Plates or baffles used to prevent oil being mixed with air or drawn through air pipes.

Oil Strainer

The mesh filter on the end of an oil pick up pipe.

Oil-Based Paints

Paints which dry by absorbing oxygen from the atmosphere. This 'uptake of oxygen' promotes a chemical reaction which is irreversible.

On Board Diagnostics (OBD)

See OBD

One-way Clutch

An automatic mechanical clutch that permits drive from one shaft to another in one direction only. A drive transmitted to the outer hub of the clutch bypasses the inner hub and the clutch free wheels. This type of clutch allows drive to be transmitted by two alternative routes and at different rotational speeds.

Opacimeter

Smoke meter used to measure the amount of smoke in diesel engine exhaust gases.

Opacity

The ability of a paint film to obliterate the colour or pattern of a surface. Opacity is measured by determining the minimum thickness at which a paint film will completely obscure a black and white pattern.

Opaque

Impervious to light transmission -non-transparent.

Open Circuit

Applied to an electrical circuit when the switch is 'off' or the circuit is not continuous.

Open Coat

A type of abrasive paper coating in which the abrasive particles are scattered in a low density to prevent it from clogging up. Typically found in Production Papers

Open Period

(1) The number of degrees of distributor rotation during which the primary circuit remains open. (2) The number of degrees of crankshaft rotation during which an inlet or exhaust valve remains open.

Open-loop

An electronic control system using a comparison of sensor signals and a pre-programmed map.

Operational Safety

Safety aspects that are operational during use of a vehicle.

Optical Gauge

A measuring instrument that uses light/reflection to align steering (for example).

OPTL

One Person Test Lane. These are lanes authorised by VOSA to conduct testing where the tester has the option of not using an assistant if so desired.


Orange cables

These indicate high voltages – take care.

Orange Peel

An irregularity in the surface of a paint film resulting from the inability of the wet film to "level out" after being applied, caused by a lack of flow. Orange peel appears as a characteristically uneven or dimpled surface to the eye, but usually feels smooth to the touch.

Orbital Sander

Type of sander that uses a circular motion to accomplish the sanding of different materials.

Organic Materials

Compounds composed of carbon, hydrogen, and other elements with chain or ring structures.

Orifice

A hole, usually with a precise drilling diameter to control a fluid flow or spray.

OS

Oxygen Sensor

Oscillate

To move or swing from one place to another (e.g. side to side).

Oscillator

An electronic circuit that produces as signal of a set frequency.

Oscilloscope

Also shortened to ‘scope'. An instrument that draws an image to represent changes in voltage over a set time period.

Otto Cycle

An alternative term for the four stroke engine cycle using the name of its inventor.

Out-of-round

A term used to describe a component that should be perfectly round or cylindrical but is not. Usually caused by wear but can be from faulty machining.

Outdoor Exposure

The most realistic way to measure the behaviour of a paint film. Manufacturers paint sample panels and leave them exposed to the elements for long periods of time, and inspect them at intervals to measure the effects of the exposure.

Outer Races

The outside rings of ball or roller bearings.

Outgoing Telephone Call

To make a telephone call to somebody.

Outlet Ports

Used to describe any port that allows a gas or liquid to leave. Exhaust ports are a good example.

Output

Power or data that comes out from a mechanical unit or electronic control module. Usually adapted or modified by the unit or module to suit a particular purpose.

Output Circuit

The battery charging circuit for the electrical current from a generator.

Output Device

A device that allows information from the computer to be displayed. Egg, monitor, printer.

Output Shaft

Shaft that outputs drive from a gearbox to a propshaft or final drive.

Oven

Equipment used to bake paint finishes. Originally developed by vehicle manufacturers, whose applied finishes may require temperatures as high as 180°C to cure. In the refinishing industry, ovens are used to bake sprayed coatings at varying temperatures up to 80°C, producing fully-cured finishes in as little as 20 minutes.

Over-thin

To add more thinner or reducer to a paint than is normally necessary for application. This is sometimes done in order to lower the paint viscosity, to aid in blending, or to achieve a special colour effect with metallics or pearlescents

Overall Painting

A type of refinish task in which the entire car is completely repainted.

Overall Ratio

The term used to describe the output ratio of a series of mechanical components such as gears or levers.

Overbake

The result of curing a paint film at too high temperature, or for longer than the specified time. The film often becomes too hard and brittle.

Overdrive Gear

A gear drive that increases the rotational speed of the output shaft above that of the input shaft.

Overdrive Unit

A separate unit that at one time was fitted on the output shaft of a gearbox. It produces a higher gear ratio.

Overlap

The area of coverage in which one spray pass is extended over and partly covered by the next pass.

Overlap (Valve)

The term used to describe the angle of crankshaft rotation when the inlet and exhaust valves are both open.

Overrun

Movement of vehicle when engine is not under power. Engine braking.

Overrun Clutch

(1) A clutch on a starter drive pinion that prevents the engine from driving the starter motor after the engine has started. (2) A one-way clutch in an automatic transmission.

Overspray

An overlap of dry spray particles landing on areas that were not meant to be painted, or on previously painted areas where they do not blend in.

Oversteer

Steering condition of a turning vehicle when the vehicle attempts to turn by a greater degree than the steered position taken by the driver. A difficult driving condition requiring opposite lock to control.

Oxidation

The chemical combination of oxygen and the binder of synthetic-enamel type paints which leads to drying. Also refers to the destructive combination of oxygen with a dry paint film leading to age degradation, or the destructive combination of oxygen and metal commonly known as Corrosion.

Oxygenated Solvent

An organic solvent containing oxygen as part of the molecular structure. Alcohols and ketones are oxygenated compounds often used as paint solvents.

Ozone

A colourless gas (O3) soluble in alkalis and cold water; a strong oxidizing agent; can be produced by electric discharge in oxygen or by the action of ultraviolet radiation on oxygen in the stratosphere (where it acts as a screen for ultraviolet radiation).


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