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Radiator Glossary of Terms
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| Three-Way Converter (TWC) |
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A catalytic converter that oxidizes hydrocarbons and carbon monoxide, and also reduces oxides of nitrogen emissions. Usually, it has separate chambers, the one upstream handling reduction, and the one downstream handling oxidation. The noble metals used a
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| Thinner |
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A solvent used to thin paints and enamels prior to application.
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| Thermostatic Switch |
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A component (sometimes adjustable) used in a cycling clutch A/C system to engage and disengage the compressor clutch. It prevents water (condensate) from freezing on the evaporator core. It also controls the temperature of air flowing out of the evaporato
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| Thermostatic Expansion Valve (TXV) |
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A component in the refrigeration system that controls the rate of refrigerant flow into the evaporator. This is done by means of a temperature sensing bulb that causes the valve to open or close in response to temperature changes in the evaporator.
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| Thermostat |
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A valve, located in the cooling system of an engine, which is closed when cold and opens gradually in response to engine heating, controlling the temperature of the coolant and rate of coolant flow.
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| Thermistor |
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A device that changes electrical resistance as temperature changes. A coolant sensor and air temperature sensor are thermistors.
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| Thermal Breakdown |
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The reaction of motor oil to high levels of heat in an engine. See Volatility. Thermal breakdown leads to increased oil consumption and can cause increased deposits and acid buildup.
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| Tetrafluoroethane |
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Chemical name of R-134a refrigerant.
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| Test Pipe |
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A short piece of exhaust pipe that's designed to replace a catalytic converter in an exhaust system-supposedly while you test the results of the switch (See Catalytic Converter). Test pipes are illegal and you can be fined if you're caught with one on you
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| Temporary Loss In Viscosity |
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Viscosity loss that occurs when the shear force is applied (i.e. only when the engine is running). When the force is removed the oil returns to its original viscosity.
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| Throttle Body Injection (TBI) |
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A type of electronic fuel injection system that uses a single injector or pair of injectors mounted in a centrally located throttle body. The throttle unit resembles a carburetor except that there is no fuel bowl, float or metering jets. Fuel is sprayed d
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| Throttle Position Sensor (TPS) |
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A little gadget on the carburetor throttle linkage or fuel injection throttle body that keeps the engine control computer informed about the throttle opening (See Computerized Engine Controls).
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| Thrust Angle |
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The angle between the thrust line and centerline. If the thrust line is to the right of the centerline, the angle is said to be positive. If the thrust line is to the left of center, the angle is negative. It is caused by rear wheel or axle misalignment a
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| Thrust Angle Alignment |
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Aligning front toe to the rear thrust angle instead of the vehicle's centerline to compensate for rear axle steer.
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| Thrust Line |
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A line that bisects total rear toe. It defines the direction the rear wheels are pointed. The thrust line should correspond to the centerline for the vehicle to steer straight.
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| Tie Rod |
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A part of the steering linkage that connects the steering arms on the knuckles to the steering rack or center link.
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| Tie Rod End |
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A flexible coupling in the steering linkage that connects the tie rods to the steering knuckles. Some require periodic greasing (twice a year or every 6,000 miles) while others are sealed. detected by raising the suspension and rocking the front wheel bac
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| Tie Rod Sleeves |
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A part of the tie rod assembly that is threaded internally and is turned to shorten or lengthen the tie rod to adjust toe alignment.
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| Timing Light |
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A strobe light for checking ignition timing. The light is connected to the number one spark plug wire so every time the plug fires the light flashes. The light is then aimed at the timing marks on the crankshaft pulley or flywheel to read timing.
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| Tire Ratings |
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On the sidewall of every tire is information about tire size, maximum load rating, maximum inflation pressure, tire construction (See Radial Tire) and performance standards. Treadwear is a comparative rating of how long the tire will last compared to othe
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| Tire Rotation |
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Switching front tires to the rear and the rear to the front to ensure even wear.
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| Toe |
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The difference between the front and rear edges of tires mounted on an axle. Toe-in means the front edges are closer together than the rear edges and tires point inward. Toe-out means the front edges are farther apart than the rear edges and the tires poi
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| Toe Wear |
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Wear across the face of the tire tread caused by slippage or scrubbing as the tire rolls along. Toe wear can produce a feathered wear pattern (bias ply tires primarily) as well as shoulder wear on radial tires. It results from too much toe-in or toe-out,
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| Top Dead Center (TDC) |
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The point at which the piston reaches the top of its travel on the compression stroke.
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| Torque |
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The twisting force applied to an object.
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| Torque Converter |
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A turbine used to transmit power from a driving member to a driven member via hydraulic action, providing changes in drive ratio and torque. In automotive use, it links the drive plate at the rear of the engine to the automatic transmission.
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| Torque Steer |
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The annoying tendency of some front-wheel drive vehicles to pull to one side when engine torque is applied. In other words, you step on the gas and the car wants to steer right or left. By redesigning the power train to use equal length half shafts betwee
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| Torque Wrench |
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A special wrench with a built-in indicator that shows you how much force you're applying to a bolt. A torque wrench should always be used when doing any type of major engine work, when tightening fasteners on the brake system or suspension, when tightenin
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| Torsion Bars |
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A steel bar that is twisted to support the weight of the vehicle. Torsion bars are used in place of coil or leaf springs on some vehicles, and allow ride height to be adjusted to compensate for sage that occurs over time.
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| Total Base Number |
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Indication of oil's ability to neutralize the effect of high-sulfur diesel fuels.
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| Total Toe |
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The combined toe reading of a pair of wheels on a given axle. Total toe is the difference between the leading and trailing edges of both tires with respect to one another. It may be specified in inches, millimeters or degrees.
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| Towing |
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Most vehicles can tow a moderate amount of weight (1000 lbs. or less) without too much trouble. But for heavier loads, the suspension and cooling system may require beefing up (See the owners manual for towing recommendations and load limits). Overload or
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| Tracking |
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How the rear wheels follow the front wheels. For proper alignment, they should follow the same path. If the rear wheels don't track straight and follow slightly to one side due to rear axle or toe misalignment, the result can be off-center steering and ac
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| Trailing Arms |
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Components in the rear suspension that connect the rear axle or spindles to the chassis.
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| Transaxle |
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The transmission in a front-wheel drive vehicle. It combines both transmission and differential into one assembly.
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| Transducer |
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device used to change a force into an electrical signal.
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| Transistor |
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A semi-conductor component that can be actuated by a small voltage to perform an electrical switching function.
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| Tread |
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The region of a tire designed to contact the ground. It is molded of tough rubber for high traction and low wear.
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| Tread Pattern |
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The arrangement of blocks, grooves, sipes, and channels designed into the tread to enhance its grip. Also called the tread design.
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| Tread Void |
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Areas in the tread, such as grooves and channels, that permits water to drain away from the footprint.
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| Traction Control |
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An enhancement of an existing ABS system that prevents wheel spin while accelerating on wet or slick surfaces. It uses the same wheel speed sensors to monitor wheel speed during acceleration, but requires some additional control solenoids and a pump to ap
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| Transmission |
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The gearbox that multiplies engine torque via gear reduction and/or torque conversion. A typical manual transmission has four or five speeds, with the final or highest gear being either a direct 1:1 drive ratio or an "overdrive" ratio (less than 1:1). An
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| Treadwear |
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The measure of the life of a tire tread.
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| Tread-Wear Indicators |
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When a tire's treads have been worn down to 1.5 mm, small bands of hard rubber will be appear across the treads themselves to indicate the level of wear.
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| Trouble Codes |
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A code number generated by a vehicle's onboard computer that corresponds to a specific fault. Most computerized engine control systems have a certain amount of self-diagnostic capability. When the engine is running and the computer detects a problem in on
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| Tubeless |
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A tire construction that uses a rubber innerliner inside the casing to prevent air leakage and eliminate the need for an inner-tube.
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| Tune-Up |
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regular maintenance, usually associated with the replacement and adjustment of parts and components in the electrical and fuel systems of a vehicle for the purpose of attaining optimum performance.
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| Turbocharger |
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An exhaust driven pump that compresses intake air and forces it into the combustion chambers at higher than atmospheric pressures. The increased air pressure allows more fuel to be burned and results in increased horsepower being produced.
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| Turbocharging |
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A method of increasing power and decreasing emissions by rerouting hot exhaust gasses through a turbine, which drives a pump that forces more air into the engine's cylinder.
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| Turning Plates |
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Plates on an alignment rack that go under the front wheels and allow the wheels to be steered 20 degrees to either side to measure toe-out on turns.
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| Turning Radius |
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The diameter of the smallest circle in which a vehicle can complete a U-turn. Turning radius depends on the wheelbase of the vehicle (longer vehicles usually need more space to turn around), and maximum steering angularity.
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| Twin I-Beam |
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A type of independent front suspension used on Ford pickup trucks that used two parallel I-beam axles (one for each wheel). The design combines the superior strength of an I-beam suspension with the flexibility and ride comfort of an independent suspensio
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| Two-Second Rule |
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The minimum distance that should be kept between two vehicles traveling in the same direction on the same road. When the vehicle ahead passes a road marker or sign, the car behind it should pass the same marker or sign roughly two seconds later. In the ca
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| Temperature |
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Heat intensity measured in degrees. Engine operating temperature is a critical factor in engine performance and emissions. Brake temperature can affect the operation of the brakes.
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| TDC |
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Abbreviation for Top Dead Center. This is the point at which the piston reaches its uppermost position in the cylinder. Ignition timing is usually expressed as so many degrees before top dead center (BTDC) or after top dead center (ATDC). A timing mark on
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| Tachometer |
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A device used to measure the rotary speed of an engine, shaft, gear, etc., usually in rotations per minute.
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