Automotive terms explained
Your car’s radiator is the main component that keeps the engine from overheating. Coolant circulates through engine passages, absorbs heat, then flows to the radiator where air passing through the fins pulls that heat away. If the radiator fails, the engine temperature climbs fast, often leading to warped cylinder heads, a blown head gasket, or…
An emissions test measures the pollutants coming out of your vehicle’s tailpipe and verifies that the onboard diagnostic system (OBD2) is functioning correctly. Most U.S. states require periodic testing—usually every one or two years—for registration renewal. The test takes about 15–30 minutes and returns a simple pass or fail. If your check engine light is…
The air-fuel ratio (AFR) is the mass of air mixed with each unit of fuel in your engine’s cylinders. For gasoline at sea level, the stoichiometric ratio is 14.7 parts air to 1 part fuel (14.7:1). A rich mixture has less air (lower number, e.g., 12:1), and a lean mixture has more air (higher number,…
A diesel particulate filter (DPF) traps soot from the exhaust to meet EPA emissions standards. It burns off trapped particles through regeneration—either passively (highway driving) or actively (the engine computer injects extra fuel to raise exhaust temperature). When regeneration fails, the filter clogs, triggering warning lights, power loss, and higher fuel consumption. Your driving pattern…
Ethanol is a grain alcohol blended into gasoline primarily to boost octane and reduce tailpipe emissions. Most pump gas in the U.S. is E10 (10% ethanol, 90% gasoline). Newer vehicles (2001 and later) can safely run E15, while only flex-fuel vehicles (FFVs) should use E85. Using the wrong blend can lead to poor performance, a…
Quick answer Octane rating measures a fuel’s resistance to engine knock (detonation). It is not a power, energy content, or cleanliness rating. The number posted on U.S. pumps is the average of two test methods: Research Octane Number (RON) and Motor Octane Number (MON), calculated as (R+M)/2. This average is called AKI (Anti-Knock Index). Common…
The Evaporative Emission Control (EVAP) system captures fuel vapors from your gas tank and engine, preventing them from escaping into the atmosphere. It stores those vapors in a charcoal canister and purges them into the engine to be burned during normal driving. When the system fails, you’ll likely see a check engine light, smell raw…
An oxygen (O2) sensor measures the unburned oxygen in your exhaust and tells the engine computer (ECU) whether the air-fuel mixture is too rich or too lean. Every modern car has at least two: one upstream (before the catalytic converter) and one downstream (after it). The upstream sensor controls fuel trim and directly affects drivability…
A catalytic converter is an emissions control device mounted in your exhaust system that converts three harmful gases—carbon monoxide, unburned hydrocarbons, and nitrogen oxides—into less toxic compounds before they leave the tailpipe. It’s valuable because the honeycomb inside is coated with precious metals (platinum, palladium, and rhodium) that make replacement expensive, and because a failed…
A fuel filter traps dirt, rust, and debris before they reach your engine’s injectors or carburetor. On most gasoline vehicles with a serviceable filter, replacement is due every 30,000–60,000 miles—check your owner’s manual. When the filter clogs, it restricts fuel flow and causes hesitation under load, hard starting, rough idle, or a check engine light…