Why is it difficult to start a car when it's hot?
3 Answers
Difficulty in starting a hot sedan is often caused by excessive carbon deposits in areas such as the throttle body, idle speed motor, intake manifold, and combustion chamber. Below is a detailed explanation of the reasons: Carbon Deposits: Carbon deposits have a strong adsorption effect on gasoline. If there are excessive carbon deposits on the intake valve, throttle body, or piston, they can absorb some fuel, leading to an overly lean air-fuel mixture, which affects starting. Damaged or Leaking Carbon Canister Solenoid Valve: The carbon canister solenoid valve controls the flow of fuel vapor from the carbon canister. After the engine is turned off, gasoline vapor mixes with fresh air in the canister and is stored in the activated carbon canister. When the engine starts, the solenoid valve between the activated carbon canister and the intake manifold opens, allowing the gasoline vapor in the canister to be drawn into the cylinders by the vacuum in the intake manifold, where it is burned. Ignition Coil: When the ignition coil heats up, the resistance of the wires increases, weakening the primary current. As a result, the voltage in the secondary coil decreases, leading to weaker sparks. This reduction in ignition energy may cause difficulty in starting the engine.
I've been driving sedans for over 20 years and have encountered hot-start difficulties several times, which is quite annoying. It's usually because when the engine gets hot, the coolant temperature sensor malfunctions, providing incorrect temperature readings that lead to miscalculated fuel injection quantities and an imbalanced air-fuel mixture. The fuel system often causes trouble too - gasoline evaporates faster in hot weather, and the fuel pump or injectors may get clogged, resulting in insufficient fuel supply during startup. Another factor is the ignition system overheating, with issues like worn spark plugs or leaking ignition coils throwing off the ignition timing. On my own car, cleaning the fuel injectors and replacing the sensor solved the problem. I recommend not delaying repairs, otherwise you risk the hassle of breaking down midway. Regular maintenance can prevent these issues from occurring in the first place.
As a car enthusiast, I've done quite a bit of research on hot-start failures, and it's quite fascinating. The causes often involve ignition components failing under high temperatures, such as severely carbon-fouled spark plugs that can't ignite properly when the engine is hot, or ignition coils that crack or short-circuit when overheated. In the fuel system, increased gasoline evaporation when hot can lead to insufficient fuel pressure or air entering the fuel lines. I've also found that carbon buildup in the intake manifold can exacerbate the issue. I've personally performed checks using a multimeter to measure sensor resistance, making it easy to pinpoint the fault. I recommend regularly replacing spark plugs, cleaning the fuel system, and keeping the engine cool. Addressing this issue isn't too complicated, and preventive measures can save a lot of hassle.
