Site hosted by Build your free website today!


A  B  C  D  E  F  G  H  I
 J  K  L  M  N  O  P  Q
R  S  T  U  V  W  X  Y  Z

Odometer see Speedometer

OEM  See original equipment manufacturer.

Ohm The unit of electrical resistance. One volt applied to a resistance of one ohm will produce a current of one amp. Ohmmeter An instrument for measuring electrical resistance.

Oil A substance that lubricates and cools the moving parts of the engine and reduces the formation of rust and corrosion. It can contain additives which fights the corrosion of bearings, keeps small particles in suspension, reduces engine wear, and reduces oxidization, minimizes carbon, lacquer, and gum formation. Oil comes in varying viscosity weights suitable for efficient operation in cold and hot weather and for engines in varying states of wear.

Oil Filler Cap The oil filler cap is a plastic or metal cap that covers an opening into the valve cover. It allows you to add oil when the dipstick indicates that you need it. Some cars have the crankcase vented through the filler cap. Oil which is added through the filler passes down through openings in the head into the oil sump at the bottom of the engine.

Oil Gauge The Oil Gauge lets you know the pressure in the oil pump; and is a direct indicator of the condition of your engine. If the oil gauge gives very low readings, it means that your oil pressure has dropped. The engine would soon grind to a halt if the oil is not forced into the nooks and crannies that need to be oiled.

Oil Pan  The pan that is bolted to the bottom of an engine. Oil returns to this pan after circulating throughout an engine to provide lubrication, as well as some cooling effects. Most oil pans are open inside, but high-performance pans can feature trap doors and baffles to control the oil during aggressive driving and keep it close to the oil pump pickup. Another product that can help control engine oil is a windage tray or a crank scraper.

Oil Pump  An engine-driven pump that delivers oil, under pressure, to the engine's moving parts.

Oil Ring  The lowermost piston ring that scrapes off excess oil from the cylinder walls and returns it to the oil pan via vents in the ring and piston.

Operating Coil see Limiting Coil

O-Ring A type of sealing ring made of a special rubber-like material; in use, the O-ring is compressed into a groove to provide the sealing action.

Original Equipment Manufacturer   A company that makes cars and/or trucks. Abbreviated OEM.


Generally speaking, overdrive (O/D) is the highest gear in the transmission. On most cars the automatic transmission has 3 speeds and overdrive (fourth speed). Overdrive allows the engine to have less rpm with higher speed for better fuel efficiency. When you switch it on, you allow the transmission to shift into overdrive mode after a certain speed has been reached (usually 30-40 mph depending on the load). When it's off, you limit transmission shifting to third speed.In normal driving conditions the overdrive should be always on.You may need to switch it off if you drive in a mountainous area. [The automatic transmission automatically shifts from O/D to 3rd gear when it feels more load. When it feels less load it shifts back to O/D, but under certain conditions, e.g., driving uphill or towing a trailer, the transmission cannot decide whether to stay in O/D or shift into 3rd speed and it starts shifting back and forth. That's the time when you may switch the O/D off and help the transmission to decide] .

You also may need to switch it off when you want to slow down using the engine braking, for example, if you're driving downhill. For more details, check your owner's manual.

Overhead Cam (ohc) Engine  An engine with the camshaft(s) located on top of the cylinder head(s).

Overhead Valve (ohv) Engine An engine with the valves located in the cylinder head, but with the camshaft located in the engine block.

Oxygen Sensor  The oxygen sensor(s) are installed in the exhaust pipe

of the vehicle. The sensor measures the oxygen level in the exhaust gases (how bad the emission is) and gives feedback to the vehicle computer, which in turn adjusts the air/fuel ratio to keep the emission low at maximum engine efficiency. If you're having problems with the emission, the oxygen sensor is one of the first things to blame.

 Also called a Lambda sensor.


A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z

Main Menu


Click the arrow above to go back where you just linked from


Contact Us

The objective of this Web Page is to familiarize you with basic auto maintenance
-  in some common emergencies -
not to make you an expert in auto mechanics

DISCLAIMER: PLEASE READ - By printing, downloading, or using you agree to our full terms. Review the full terms by clicking here. Below is a summary of some of the terms. If you do not agree to the full terms, do not use the information. We are only publishers of this material, not authors. Information may have errors or be outdated. Some information is from historical sources or represents opinions of the author. It is for research purposes only. The information is "AS IS", "WITH ALL FAULTS". User assumes all risk of use, damage, or injury. You agree that we have no liability for any damages. We are not liable for any consequential, incidental, indirect, or special damages. You indemnify us for claims caused by you.

  I am in no way, shape, or form telling you to do this yourself. Your results may vary. If something goes wrong, it is not my fault!
These are just guidelines.

Copyright © 2000 Jon's

Images, Inc. All rights reserved