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Radiator Glossary of Terms
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| SAE |
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Society of Automotive Engineers. Organization whose responsibility is to recognize and define the need for a given level of motor oil performance in line with the demands of engine builders. SAE evaluates proposed engine oil performance categories and est
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| Scan Tool |
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A hand-held electronic tool that plugs into a vehicle's diagnostic connector to access fault codes and other diagnostic information. Scan tools can be used for ABS diagnostics as well as engine and other diagnostics.
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| Schrader Valve |
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A type of valve fitting that opens when depressed. Schrader valves are used in tire valve stems, on air conditioning hoses and on the fuel rails of many fuel injection systems.
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| Scrap Thickness |
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The thickness at which a disc rotor must be discarded. Through wear and machining, a disc rotor becomes thinner over time. As a result it becomes less able to dissipate heat and more prone to warping. The vehicle manufacturer usually determines scrap thic
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| Sealed-Beam Headlight |
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Headlights composed of lens, reflector and filament fused together as a single unit.
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| Secondary Circuit |
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The high voltage side of the ignition system, usually above 20,000 volts. The secondary includes the ignition coil, coil wire, distributor cap and rotor, spark plug wires and spark plugs.
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| Section |
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A slice of a tire from one bead, through the tread to the other bead.
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| Section Height |
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The vertical distance from the bead edge to center of the crown in an unloaded tire.
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| Section Width |
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The distance between a tire's sidewalls measured at the widest part of the tire. Each size of tire is measured on a specific rim width.
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| Select Low Principle |
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An operating strategy on ABS systems that have one wheel speed sensor for each rear wheel. The control module selects the wheel that's turning the slowest to initiate antilock braking.
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| Self-Energizing |
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Property of a drum brake, whereby the braking force is increased by the braking action of the shoes against the drum.
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| Sensor |
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Any device designed to measure engine operating conditions or ambient pressures and temperatures. Usually electronic in nature and designed to send a voltage signal to an on-board computer, some sensors may operate as a simple on/off switch or they may pr
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| Scrub Radius |
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The distance between the extended centerline of the steering axis and the centerline of the tire where the tread contacts the road. If the steering centerline is inboard of the tire centerline, the scrub radius is positive. If the steering centerline is
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| Semi-Metallic Brakes |
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A type of brake lining that uses steel wool instead of asbestos as a reinforcing fiber. Semi-metallic brakes give better high temperature performance and wear characteristics then conventional asbestos linings. They are commonly used on the front disc bra
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| Sending Unit |
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A type of brake lining that uses steel wool instead of asbestos as a reinforcing fiber. Semi-metallic brakes give better high temperature performance and wear characteristics then conventional asbestos linings. They are commonly used on the front disc bra
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| Sensor Ring |
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The toothed ring that generates a signal in a wheel speed sensor. It may be mounted on the back of the wheel hub, inside the rotor or brake drum, or mounted on the transmission output shaft or differential pinion shaft. The number of teeth or notches in t
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| Series |
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A designation of a tire's aspect ratio. A tire with an aspect ratio of 60% is a 60 series tire.
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| Serpentine Belt |
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A type of flat rubber drive belt that is used to turn multiple accessories on the front of an engine. It is called a serpentine belt because of the way it snakes around the various pulleys. Many vehicles now have a single serpentine drive belt because it
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| Service Manual |
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A handbook for a specific make, model and year published by a vehicle's manufacturer, containing instructions and specifications regarding its maintenance and repair.
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| Service Writer |
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The individual at a garage or dealership responsible for writing repair orders, communicating them to the mechanic and estimating the final cost to the customer.
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| Setback |
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The amount by which one front wheel is further back from the front of the vehicle than the other. It is also the angle formed by a line perpendicular to the axle centerline with respect to the vehicle's centerline. If the left wheel is further back than t
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| Severe-Driving Conditions |
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Driving in stop-and-go traffic, frequent short trips, extreme temperatures, or towing and hauling.
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| Shackle |
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A link that connects a leaf spring to the chassis or frame. The shackle allows the length of the spring to change as the suspension moves up and down.
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| Shear Stability |
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Motor oil's ability to maintain or resist viscosity breakdown under high-shear conditions.
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| Shim |
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Spacers of precise, predetermined thickness used between pads to establish a proper working relationship.
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| Shimmy |
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Shaking or vibrations of a vehicle's front wheels from side to side due to problems with tire alignment or suspension.
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| Shock Absorber |
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An oil-filled component of the suspension system found at each wheel.
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| Shock Fade |
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A condition where loss of dampening action occurs because of fluid foaming inside a shock absorber. The rapid oscillations of the piston moving through the fluid churns it into foam, which reduces the amount of resistance encountered by the piston. This c
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| Short-Long Arm (SLA) Suspension |
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A common type of suspension that uses upper and lower control arms of unequal length. The upper arm is usually shorter than the lower arm to control camber changes during jounce and rebound.
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| Shoulder |
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The portion of the tire between the bead and the tread. It is flexible to soak up bumps yet stiff to limit tire rollover.
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| Shrinkage |
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The shrinking of automotive paint as it dries.
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| Sidewall |
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The portion of the tire between the bead and the tread. It is flexible to soak up bumps yet stiff to limit tire rollover.
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| Sight Glass |
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A window, usually located in the top of the receiver-dryer for observing the refrigerant during diagnosis. Many A/C systems do not have this device.
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| Slave Cylinder |
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In automotive use, a device in the hydraulic clutch system that is activated by hydraulic force, disengaging the clutch.
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| Slip Angle |
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The angle between the direction in which a tire is aimed or steered and the actual direction of tire travel.
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| Slip Plates |
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Movable plates on an alignment rack that go under a vehicle's wheels that allow the suspension to settle prior to an alignment.
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| Slotted Disc |
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Type of disc brake rotor that has a series of slots or grooves across its friction surfaces. These are designed to improve the bite of the pads and break down the build up of gas and dirt that can occur between pad and rotor. High-performance rotors can b
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| Sludge |
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Soft, blackish deposits found throughout an engine's interior. Consisting of a mixture of dust, oil, gasoline, water and other contaminants, sludge is formed a result of neglected oil changes.
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| Steering Effort |
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The amount of driver input or muscle it takes to turn or steer the wheels. Excessive effort can be caused by loss of power assist, binding in the steering gear, worn upper strut bearing plates or binding in ball joints or tie rod ends. Excessive caster ca
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| Steering Geometry |
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A general term used to describe the angular relationships between the wheels, steering linkage and suspension.
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| Steering Knuckle |
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A forging that usually includes the spindle and steering arm, and allows the front wheel to pivot. The knuckle is mounted between the upper and lower ball joints on a SLA suspension, and between the strut and lower ball joint on a MacPherson strut suspens
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| Steering Return |
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The ability of the steering wheel to self-center after turning. Causes of poor returnability include excessive caster or binding in the steering column, steering gear, ball joints, upper strut bearing plates or tie rod ends.
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| Smart Suspensions |
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Any suspension that uses computer-controlled shock absorbers and/or air springs to vary ride characteristics and/or ride height. The advantage of such a suspension is that it can change the way the suspension reacts to changing road conditions. On a rough
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| Smog Pump |
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A slang term for an air injection system pump. Used to pump extra air into the exhaust system to help the converter reburn pollutants.
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| Snap Rule |
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The EPA's "Significant New Alternatives Policy." This was implemented in July 1994 for the purpose of approving alternative refrigerants for automotive use. Under this rule, a manufacturer must submit refrigerant data to the EPA for review. If the alterna
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| Solenoid |
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A coil used to produce a magnetic field, the effect of which is to produce work.
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| Solid Rotor |
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Disc rotor with solid metal between the two friction surfaces.
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| Solubilize |
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To dissolve one material into another. In the case of cleaning fluids, the solute, or substance being dissolved, is often some type of soil. This soil then is dissolved in the cleaning fluid and can be washed away during a rinsing process.
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| Spare Tire |
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There are several different types of spare tires: a folding spare (which must be inflated with an air canister prior to mounting), a compact spare (which is much smaller and narrower than the other wheels on the vehicle), and a lightweight spare (which is
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| Spark Knock |
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This is the pinging or rattling noise sometimes heard during acceleration that indicates detonation is occurring inside the engine (See Detonation). Spark knock can be caused by a variety of things including using low octane fuel, over-advanced ignition t
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| Spark Plug |
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A device screwed into the combustion chamber of a spark ignition engine. The basic construction is a conductive core inside of a ceramic insulator, mounted in an outer conductive base. An electrical charge from the spark plug wire travels along the conduc
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| Specific Gravity |
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Ratio of the weight of a volume of motor oil to the weight of an equal volume of water at a specified temperature (usually 60o F)
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| Specific Output |
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The power derived from each liter of engine displacement. Also known as horsepower per liter.
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| Specifications |
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A listing of the measurements for all of a car's components.
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| Speed Rating |
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A letter designation identifying the tire's high-speed durability on an indoor test wheel.
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| Spindle |
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The component on which the hub and wheel bearings are mounted.
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| Splines |
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Ridges machined or cast onto the outer diameter of a shaft or inner diameter of a bore to enable parts to mate without rotation.
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| Spoiler |
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An aerodynamic add-on that goes across the trunk or back of a vehicle to deflect the direction of airflow and reduce drag. A front spoiler is technically an "air dam" because it prevents air from getting under the car and increasing drag.
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| Spongy Pedal |
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Pedal that feels spring-like, perhaps due to the presence of air in the hydraulic system.
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| Spring |
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A suspension component that supports the weight of the vehicle. Basic types include coil springs, leaf springs, air springs and torsion bars. Spring height affects ride height, which in turn affect wheel alignment. Weak or sagging springs should be replac
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| Spring Compressor |
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A tool for compressing and holding a coil spring so it can be removed or replaced, or to allow the disassembly of a MacPherson strut.
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| Stability Control |
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A type of advanced antilock brake/traction control system that uses the brakes to assist steering maneuvers and to help improve vehicle handling and stability as driving conditions change. The system includes various sensors that monitor the driver's stee
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| Starburst Symbol |
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Oils that display the starburst symbol must meet the requirements of ILSAC GF-2 to display the mark. The requirements are: Oil must meet requirements for low-temperature pumping/cranking (essentially oil must be a l0W or lower W grade), gelation index (a
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| Static Balance |
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Wheel balance that depends on an equal distribution of weight around the circumference of the wheel and tire assembly. Static balance can be achieved without spinning the wheel by using a bubble balancer. A wheel that lacks static balance will shake or tr
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| Static Wheel Loading |
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The amount of weight forced onto each road wheel in a stationary car, as a result of a car's (usually uneven) weight distribution.
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| Steering Arm |
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The arms on the steering knuckles (or struts) to which the tie rods are attached to steer the wheels.
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| Steering Damper (Stabilizer) |
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A hydraulic device similar to a shock absorber attached to the steering linkage to absorb road shock and steering kickback.
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| Steering Axis Inclination (SAI) |
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The angle formed by a line that runs through the upper and lower steering pivots with respect to vertical. On a SLA suspension, the line runs through the upper and lower ball joints. On a MacPherson strut suspension, the line runs through the lower ball j
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| Stop-And-Go Driving |
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This type of driving is especially hard on a vehicle because the engine spends most of it time at idle where it works less efficiently. Because the water pump is turning slowly at idle, the cooling system can overheat on a hot day. Continual stopping and
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| Straight Weight |
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Motor oil suitable for use within a narrow range of temperatures outside of which its flow characteristics will not adequately lubricate.
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| Strut Towers |
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The panels or structural members in a unibody to which the upper strut mounts are bolted. The position of the towers is important because it affects camber and caster readings.
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| Subcooling |
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The process of removing heat from refrigerant after condensation.
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| Subframe |
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The lower frame rails and structural members that comprise the lower elements of a unibody. Steering and suspension components may be attached directly to the subframe, or to a "cradle" or "crossmember" that bolts to the subframe.
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| Suction Line |
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Connects the evaporator outlet and compressor inlet. Low pressure refrigerant vapor is drawn from the evaporator to the compressor through this line.
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| Suction Pressure |
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Compressor intake pressure as indicated by a manifold gauge set.
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| Suction Side |
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The portion of an A/C system under low pressure, the area between the evaporator and compressor inlet.
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| Sulfated Ash |
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A noncombustible motor oil residue resulting from detergents and metallic additives.
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| Supercharger |
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Also called a "blower," a supercharger is a device that forces more air and fuel into the engine to increase horsepower. Unlike a turbocharger (See Turbocharger), a supercharger is belt or gear driven and provides instant boost pressure to the engine at a
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| Superheat |
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The difference between A/C evaporator inlet and outlet temperatures. It is created in the evaporator as liquid refrigerant changes into vapor.
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| Superheated Vapor |
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Refrigerant vapor at a temperature that is higher than its boiling point at a given pressure.
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| Suspension System |
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A system of springs and shock absorbers that cushion the passenger compartment of the car from the bumps and shocks.
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| SUVA |
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DuPont's trade name for tetrafluoroethane or R-134a refrigerant.
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| Sway Bar |
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A component that's often used in a suspension system to control body roll. A sway bar may be used on the front and/or rear suspension to help keep the body flat as the vehicle rounds a corner. This greatly improves a vehicle's cornering agility. Replacing
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| Swept Area |
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Total friction area contacted by the pads during one revolution of the rotor.
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| Swirl Combustion |
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The deliberate motion of the fuel-air mixture in a vortex or whirlwind pattern to facilitate mixing during combustion for fast burning.
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