Dictionary of Automotive Terms Abbreviations

DICTIONARY OF AUTOMOTIVE TERMS - "Me"

MEA: Acronym for Membrane Electrode Assembly

Mean: See
Indicated mean effective pressure

Mean distance to the sun: 240 million miles; used to specify the headroom in convertibles

Mean effective pressure

(MEP)

The average pressure of the burning fuel on the Power stroke subtracted by the average pressure on the other three strokes. Pressure is in pounds per square inch.
Average pressure on a surface when a changing pressure condition exists.

Also See
Brake mean effective pressure
Indicated mean effective pressure

Mean indicated pressure: A mathematical value that indicates the relation between the effective area of the work diagram of the two-stroke engine and the movement of the piston

Mean time to repair: (MTR) The time interval (hours) that may be expected to return failed equipment to proper operation.

Measuring: See
Ionic-current measuring technique
Pushrod measuring tool

Measuring method: See
Ionic-current measuring method

Measuring technique: See
Ionic-current measuring technique

Measuring tool: See
Pushrod measuring tool

Mechanic: A person who works on engines or machines.

Also See
Automobile mechanic
Backyard mechanic
DIY mechanic
Do-it-yourself mechanic

Mechanical advance: See
Centrifugal advance

Mechanical advantage: The ratio of the force exerted to the force applied. A manual brake pedal may have a mechanical advantage, or pedal ratio of 5 to 1.

Mechanical bond: The joining of two or more materials by holding them together with bolts or clamps

Mechanical brake: See
Mechanical brakes.

Mechanical brakes: Service brakes that are actuated by a mechanical Linkage such as rods or cables (rather than Hydraulic lines) connecting the brakes to the Brake pedal. The Parking brake on most vehicles is mechanical.

Mechanical cycle: Cycle which is a repetitive series of mechanical events.

Mechanical degree: The popular physical understanding of degrees (360°=1 rotation)

Mechanical efficiency: An engine's rating as to how much of the Potential Horsepower is wasted through Friction within the moving parts of the engine. The ratio between the Indicated horsepower and the Brake horsepower of an engine.

Mechanical face seal: A shaft seal consisting of two highly polished mating surfaces, one surface being connected to the shaft (rotating element) and the other to the casing (stationary element)

Mechanical fade: Brake fade caused by heat expansion of the brake drum away from the brake linings. Not a problem with disc brakes.

Mechanical galvanizing: See
Mechanical plating

Mechanical-hydraulic booster: A power booster that uses hydraulic pressure from the power steering pump to increase brake application force.

Mechanical ignition timing: Centrifugal and vacuum advance

Mechanical Interrupter: A device which provides for mechanical closure of the fuel flow to the main burner by positive means such as an applied manual force through a linkage, lever handle, spring or similar mechanical means.

Mechanical plating: A deposition of zinc on another material by a cold-peening process, such as tumbling

Mechanical Properties: Those properties of a material that reveal the elastic and inelastic reaction when force is applied, or that involve the relationship between stress and strain; for example, the modulus of elasticity, tensile strength and fatigue limit.

Mechanical protection: Where clogging materials are present in severe proportions, the air gap of Open enclosure electric motors may become clogged. Therefore, the recommendation is a Totally enclosed motor housing to obtain mechanical protection from the elements.

Mechanical seal: A shaft seal consisting of two highly polished mating surfaces, one surface being connected to the shaft (rotating element) and the other to the casing (stationary element)

Mechanical stress: A force acting across a unit area in solid materials in resisting the separation, compacting, or sliding that tends to be induced by external forces

Mechanical surface treatment: A production of a dull or rough surface or a decorative finish by grinding, brushing, polishing, or abrasive blasting

Mechanic installed market: (MIL) Vehicle maintenance and repair conducted by a mechanic/professional at a service outlet.

Mechanic's creeper: See
Creeper

Mechanic's elbow: A shallow dent in body panels, usually on the top of a fender near the engine compartment; caused when leaning over into the engine compartment and supporting the body with elbows on the fender

Mechanics lien: When you take your vehicle to a shop to be repaired and you fail to pay your repair bill, the repair shop has a Lien on your vehicle and can confiscate and sell your vehicle to pay for the work on your vehicle.

Mechanic's stethoscope: See
Sonoscope

Mechanism: See
Adjuster Mechanism
Gearchange mechanism
Locking mechanism
Quick Return Mechanism
Shifter mechanism
Triggering Mechanism
Vacuum advance

MECP: Acronym for Mobile Electronics Certification Program.

MECS

Acronym for Mazda Electronic Control System
Acronym for Manufacturing Energy Consumption Survey

Media: See
Hardening Media

Median: The area that divides traffic moving in opposite directions on a single roadway.
See
Center median

Median island: See
Central median island

Median space: A gap provided in the center of a dual carriageway to allow vehicles to cross through or turn onto another road

Medium carbon steel: A type of carbon steel used extensively for sheet metal screws and grade 2 hex head bright cap screws.

Medium-duty truck: Vehicle weighing from 10,001 to 25,000 lbs.

Medium pressure: For valves and fittings, implies that they are suitable for working pressures between 125 to 175 pounds per square inch.

Medium-temperature collector: A collector designed to operate in the temperature range of 60°C to 82°C, but that can also operate at a temperature as low as 43°C. The collector typically consists of a metal frame, metal absorption panels with integral flow channels (attached tubing for liquid collectors or integral ducting for air collectors), and glazing and insulation on the sides and back.

Megajoule: (MJ) An SI measurement of energy (= l000 joules)

Megger: A portable instrument used to measure insulation resistance. It consists of a hand-driven DC generator and a direct reading ohm meter.

Megohm: A unit of measure for electrical resistance. One megohm is equal to a million ohms.

Megohmmeter: Instrument for measuring extremely high resistances (in the millions of ohms ranges).

Melting Equivalent: See
Ice Melting Equivalent

Melting point: Temperature at atmospheric pressure at which a substance will melt.

MEMA: Acronym for Motor and Equipment Manufacturers Association.

Member: A general term that refers mainly to the side rails and crossmembers but also to any structural hollow-section part on a vehicle.

Also See
Box member
Cross member
Frame member
Main member
Nondisplaceable Rotor Member
Rupture Member
Side member
Stressed Member

Member of the gear train: Sun gear, internal gear, and planet carrier are the members of a planetary gear train

Membrane: The separating layer in a fuel cell that acts as electrolyte (a ion-exchanger) as well as a barrier film separating the gases in the anode and cathode compartments of the fuel cell.
Also see
Catalyst Coated Membrane
Proton Exchange Membrane
Sill membrane

Membrane electrode assembly: (MEA). Structure consisting of a proton-exchange membrane with surfaces coated with Catalyst/carbon/binder layers and sandwiched by two microporous conductive layers (which function as the gas diffusion layers and current collectors).

Membrane Fuel Cell: See
Proton Exchange Membrane Fuel Cell

MEMCAL: Acronym for Memory Calibration

Memory: See
Fault memory
Keep alive memory
Last station memory
Non-volatile Random Access Memory
Programmable Read Only Memory
Random Access Memory
Read Only Memory

Memory button: A button which operates the position of electric seats, mirrors, etc. and which stores the requirements of a particular driver in its memory

MEP: Acronym for Mean effective pressure.

MERA: Acronym for Mobile Electronics Retailers Association.

Mercaptan: An organic chemical compound that has a sulfur like odor that is added to natural gas before distribution to the consumer, to give it a distinct, unpleasant odor (smells like rotten eggs). This serves as a safety device by allowing it to be detected in the atmosphere, in cases where leaks occur.

Mercedes: Click image for books on
Mercedes

A vehicle brand of which the 1925-1948 models with required application are Classic cars.

Mercedes-Benz: Click image for books on
Mercedes-Benz

A German vehicle brand which began in 1871, of which all 230 and up, and K, S, SS, SSK, SSKL, Grosser and Mannheim models with required application are Classic cars. The 1955-61 190 SL models are Milestone cars. The 1951-54 220A Coupe and Convertible are Milestone cars. The 1956-65 220S/220SE Coupe and Convertible are Milestone car. The 1963-67 230SL Coupe and Convertible are Milestone cars. The 1965-67 250SE Coupe and Convertible are Milestone cars. The 1965-67 250 SL models are Milestone cars. The 1969-70 280 SL models are Milestone cars. The 1965-67 300 SE Coupe and Convertible are Milestone cars. The 1952-64 300 S, SL, SE, 300 Coupe and Convertible are Milestone cars. The 1964 600 model is a Milestone car. The 1965-70 SWB-LWB 600 models are Milestone cars. It also includes the following 190D (19__-89), 190E (1982-93), 260E (19__-89), 300CE (19__-93), 300D (1990-93), 300E (19__-93), 300SD (1992-93), 300SE (19__-93), 300SEL (19__-91), 300SL (1990-93), 300TE (19__-93), 350SD (1990-91), 350SDL (1990-91), 400E (1992-93), 400SE (1992), 400SEL (1993), 420SEL (19__-91), 500E (1992-93), 500SEC (1993), 500SEL (1992-93), 500SL (1990-93), 560SEC (19__-91), 560SEL (19__-91), 560SL (19__-89), 600SEC (1993), 600SEL (1992-93), 600SL (1993), C-Class (1994-08), CL-Class (1998-2007), CLK-Class (1998-2008), CLS-Class (2006-07), E-Class (1994-2008), G-Class (2002-06), GL-Class (2007), ML-Class (1998-2007), R-Class (2006-07), S-Class (1994-2008), SL-Class (1994-2007), and SLK-Class (1998-2008)

Mercer: A vehicle brand of which the 1925-1948 models are Classic cars.

Mercoid bulb: Electrical circuit switch which uses a small quantity of mercury in a sealed glass tube to make or break electrical contact with terminals within the tube.

Mercosur: The southern zone common market of Argentina, Brazil, Paraguay, and Uruguay. Mercosur enacted a common external tariff on January 1, 1995 for almost 85 percent of tariff items of the four countries; most trade among members will be duty-free.

Mercury: Click image for books on
Mercury

A vehicle brand of the Ford Motor Company which began in 1939 and of which the 1967-68 Cougar XR-7 models are Milestone cars. The 1946 Sportsman is a Milestone car. The 1954-55 Sun Valley models are Milestone cars. It includes the Capri (1991-94), Cougar (1967-2002), Grand Marquis (1979-current), Marauder (2003-04), Mariner (2005-08), Milan (2006-07), Montego (2005-07), Monterey (2004-07), Mountaineer (1997-2008), Mystique (1995-2000), Sable (1986-2005, 2008-current), Topaz (1984-94), Tracer (1988-99), and Villager (1993-2002)

Mercury barometer: A device used to determine atmospheric pressure by observing the height of a column of mercury

Mercury column: A reference term used in connection with a manometer

Mercury switch: Safety switch to prevent erroneous deployment of the air bag. Due to ecological problems associated with mercury in automobile waste, mercury switches are being replaced by suspended-mass switches, e.g., a Hamlin switch

Mercury vapor lamp: A high-intensity discharge lamp that uses mercury as the primary light-producing element. Includes clear, phosphor coated, and self-ballasted lamps.

Merging: The action of a vehicle which enters the highway at approximately the same speed as the highway traffic and moves between the other vehicles to become part of the highway traffic

Merkur: Click image for books on
Merkur

A model of automobile manufactured by Ford of Europe which included Scorpio (1988-89) and XR4Ti (1985-89)

Mesh: To engage, especially gears. The opposite is Disengage.

Also See
Constant-mesh gearbox
Wire mesh

Mesh gearbox: See
Constant mesh gearbox
Constant mesh gears

Meshing drive: A device for engaging the starter pinion with the flywheel ring gear

Meshing spring: A component of a pre-engaged starter which ensures that the shift lever will move to its final position and that the starter current will be switched on in case of tooth abutment

Message center: Usually a multifunctional display of a diagnostic system. A typical messages are NORMAL, DOOR AJAR, TAILGATE OPEN, LAMP OUT, WASHER FLUID LOW, etc.

Message sign: See
Variable message sign

Met: Term applied to the heat release from a human at rest. It equals 1 8.4 Btu/sq. ft./hr. (50 kcal/m2/hr or 58 W/m2).

Metacenter: The intersection point of a vertical line drawn through the line of buoyancy of a slightly listed vessel which intersects the centerline plane

Metacentric height: The distance from the metacenter to the center of gravity of a ship. If the center of gravity is below the metacenter the vessel is stable

Metal: See
Babbitt's Metal
Base metal
Bearing Metals
Bell Metal
Blue Metal
Britannia Metal
Burned metal
Burnt Metal
Ferrous metal
Heavy sheet metal
Light sheet metal
Monel Metal
Money Metal
Noble metal
Nonferrous metal
Platinum metals
Pot metal
Scrap metal
Sheet metal
Sound metal
Weld metal
White metal

Metal-arc: See
Gas metal-arc welding

Metal-arc welding: See
Gas metal-arc welding

Metal blank: See
Sheet metal blank

Metal Bluing: See
Dykem-type Metal Bluing

Metal brake pad: See
Sintered metal brake pad

Metal cargo: Truck contents which include metal pipe, coils, metal fencing, ingots, steel plates, corrugated tin, and similar processed metal cargoes.

Metal catalyst: A catalyst whose active phase is supported by a metal substrate, i.e., sheet steel. Compare Metal monolith

Metal clamp: See
Sheet metal clamp

Metal conditioner: An acid-based metal cleaner that removes rust and corrosion from bare metal, etches it for better adhesion and forms a corrosion resistant film

Metal cutter: A bench tool for cutting sheet metal.

Also See
Sheet metal cutter

Metal fatigue: A crystallizing of the metal due to vibration, twisting, bending, etc. The unit will eventually break. Bending a piece of wire back and forth to break it is a good example of metal fatigue.
Also see
Fatigue.

Metal folder: See
Sheet metal folder

Metal forming: Solid metal and molten metal process such as casting, forging, Stamping, and machining.

Metal halide lamp: A high-intensity discharge lamp type that uses mercury and several halide additives as light-producing elements. These lights have the best Color Rendition Index (CRI) of the high-intensity discharge lamps. They can be used for commercial interior lighting or for stadium lights.

Metal Hydride: See
Nickel Metal Hydride

Metal inert gas welding: See
MIG welding

Metallic: Referring to or consisting of metal

Metallic drive screw: A British term for a Self-tapping screw

Metallic finish: A type of paint in which tiny flecks of shiny metal has been added in order to give a sparkle effect.

Metallic friction material: A sintered friction material formulated with metallic or metallic-ceramic materials.

Metallic lining: semi-metallic lining

Metallic paint: A Finish paint colors that contain both Pigment and small metallic flakes which reflect light. The opposite is solid paint. The flakes are often of different sizes. When the surface is viewed from different angles, the color shade seems to vary, since the flakes are all oriented at different angles in the paint and consequently reflect the light differently. Japanese motorcycles used a different size of flakes than was common in the USA. As a result, repainted tanks in the USA did not have the same look.

Metallize: To coat or impregnate a metal or non-metal surface with metal, as by metal spraying or by vacuum evaporation

Metallographic examination: A test to determine the structural composition of a metal as shown at low and high magnification and by X-ray diffraction methods. Tests of this type include macro-examination, micro-examination, and X-ray diffraction analysis

Metal mesh: See
Wire mesh

Metal monolith: See
Metal support

Metal remains: See
Sheet metal remains

Metal roller: See
Sheet metal roller

Metal shafts: These are used to attach the connecting rods to the crankshaft. Also called eccentric journals

Metal shears: A scissor-like hand tool for cutting sheet metal. Also called snips

Metal spraying: A coating of surfaces with droplets of molten metal or alloy by using a compressed gas stream

Metal support: A thin corrugated strips of steel alloy rolled up into a tight coil as a support for the catalyst in a catalytic converter.

Also See
Ceramic honeycomb

Metalworking: Forming and shaping metal

Metalworking spoon: See
Body spoon

METC: Acronym for Mobile Electronics Technical Center.

Meter

A device for measuring the quantity of a substance passing through it.
To measure with a meter.
To supply at a measured rate.
A distance of about a yard (actually a little over 39.37"). Also spelled metre.

Also See
Air flow meter
Air Mass Meter
Air Meter
Ampere-hour Meter
Ampere-turns Per Meter
Bouncing-pin Detonation Meter
CO meter
Demand Meter
Dwell meter
Dynamic Timing Meter
Hot-wire airflow meter
L-jetronic air flow meter
Mass airflow meter
Newton metre
Parking meter
Smoke meter
Trip meter
Vane Air-flow Meter

Metering Circuit: See
Main Metering Circuit

Metering jet: A small hole or orifice used to control the flow of Gasoline in various parts of the Carburetor.

Metering orifice: A small hole that restricts the flow of liquid -- usually coolant or oil

Metering port: A part of the metering unit in the fuel distributor

Metering rod: A thin, movable rod which varies the opening area in a Carburetor jet. As the rod is raised it permits more fuel to enter the jet.

Metering signal: A (relative) vacuum signal generated by the pressure differential that occurs at the venturi. The strength of the metering signal determines how much fuel is pulled from the main circuit into the venturi. The smaller the venturi the greater the pressure drop and the stronger the metering signal; the larger the venturi, the smaller the pressure drop and the weaker the metering signal

Metering slits: In Bosch CIS, the narrow slits in the control-plunger barrel of the fuel distributor. Fuel flows through the slits in accordance with the lift of the control plunger and the pressure drop at the slits

Metering unit: A unit which regulates the quantity of fuel injected in the K-jetronic system. A lever connected to the sensor plate raises or lowers a stepped control plunger in the metering unit. The position of the control plunger relative to the metering ports in the metering unit varies the flow of fuel to the fuel injectors

Metering valve

A valve positioned in the hydraulic line to the front brakes, on some cars with front disc and rear drum brakes. It prevents the disc brakes from applying until after the rear brake linings contact the drum. The metering valve closes off pressure to the front disc brakes until a specified pressure level is generated in the master cylinder. This allows pressure in the rear brake circuit to overcome return spring force and an gap before the hydraulic pressure is admitted to the front disc brakes
A hydraulic control valve placed in the circuit to the front brakes, designed to restrict pressure to the front brake calipers until the rear brake shoes overcome the tension of the retracting spring
A hydraulic valve used in some brake systems to slightly delay the application of front-disc brakes to obtain a balanced braking.

Methacrylate: A polymer used in toughening rubber.

Also See
Polymethyl methacrylate

Methane: (CH4) A colorless, flammable, odorless hydrocarbon gas and the principal constituent of natural gas. Pure methane has a heating value of 1,012 Btu per standard cubic foot. It is colorless and naturally odorless, and burns efficiently without many by products. Local distributors add aromas as a safety measure. It is also an important source of hydrogen in various industrial processes. Methane is a greenhouse gas.

Methanogens: Bacteria that synthesize Methane, requiring completely anaerobic conditions for growth.

Methanol: (CH3OH)A light, volatile Alcohol that is occasionally blended with Gasoline (typically 3%) to raise octane levels, it is poisonous to humans and causes trouble with rubber and plastic parts of the Fuel system not designed to handle alcohol-blended fuels. It is typically manufactured by steam reforming natural gas. Also formed in the destructive distillation of wood. Also called methyl alcohol or wood alcohol.

Methanol blend: Mixtures containing 85 percent or more (or such other percentage, but not less than 70 percent) by volume of Methanol with Gasoline. Pure Methanol is considered an "other alternative fuel".

Methanol Fuel Cell: See
Direct Methanol Fuel Cell

Methanotrophs: Bacteria that use Methane as food and oxidize it into carbon dioxide.

Method: See
Ballistic Method
Bergstroms Method
Bonding Method
Ionic-current Measuring Method
Izod Method
Quasi-elastic Method
Quinckes Method
Vicat Test Method
Waste Spark Method

Methyl alcohol: See
Methanol.

Methylated spirits: Almost pure alcohol (which has wood alcohol and coloring added to make it unfit for human consumption); used for cleaning

Methyl chloroform: (trichloroethane) An industrial chemical (CH3CCl3) used as a solvent, aerosol propellant, and pesticide and for metal degreasing.

Methylcyclopentadienyl Manganese Tricarbonyl: (MMT) An organic manganese compound. It is used as a fuel additive designed to enhance octane levels in gasoline.

Methylene chloride: A colorless liquid, nonexplosive and practically nonflammable. Used as a refrigerant in centrifugal compressors, a solvent for organic materials, and a component in nonflammable paint removers.

Methyl Ester: A fatty Ester formed when organically derived oils are combined with Methanol in the presence of a Catalyst. Methyl ester has characteristics similar to petroleum-based diesel motor fuels.

Methyl Ether: See
Tertiary Amyl Methyl Ether

Methyl Tertiary Butyl Ether: (MTBE) (C₅H₁₂O) A high octane, low volatility Ether. It is a petroleum-based product produced from Methanol and Isobutylene. It is not very toxic but is not very biodegradable. The resulting ether has high octane and low volatility. It is a fuel oxygenate and is permitted in unleaded gasoline up to a level of 15% by volume.

Metre: See
Meter

Metric century: A bicycle ride of 100 kilometers (62.14 miles).
Also see
Century.

Metric size: Units made to metric system measurements.

Metric system: Decimal system of measuring.

Metric thread

The threads of metric nuts, bolts, and screws. Two primary styles were common ISO (International Standardization Organization) and JIS (Japanese Industrial Standard) which is no longer used. UNC thread and UNF thread cannot be interchanged with any metric nut or bolt.

Nominal diameter	Width across flat		Pitch
Nominal diameter	ISO	JIS	ISO	JIS
3	5.5	6	0.5	0.6
4	7	8	0.7	0.75
5	8	9	0.8	0.9
6	10	10	1.0	1.00
8	12	14	1.25	1.25
10	14	17	1.25	1.25
12	17	19	1.25	1.5
14	19	21	1.5	1.5
16	22	23	1.5	1.5
18	24	26	1.5	1.5
20	27	29	1.5	1.5

Also see
International metric thread system

Metric Ton: A weight measure equal to 1,000 kilograms, 2,204.62 pounds, and 0.9842 long tons.

Metro driving: An American term for driving exclusively in the city rather than on the highway. The British term is urban driving.

MEWA: Acronym for Motor and Equipment Wholesalers Association.