What are the main reasons for difficulty in starting a hot engine?
2 Answers
The main reasons for difficulty in starting a hot engine are: 1. Fuel injector leakage: The more severe the fuel injector leakage, the richer the air-fuel mixture becomes, leading to difficulty in starting a hot engine; 2. Damaged carbon canister purge valve: If the carbon canister continues to supply fuel vapor to the intake manifold, it will cause an overly rich air-fuel mixture, making it difficult to start; 3. Poor fuel quality: After the engine is shut off for a while, the engine compartment remains quite hot. If the fuel is highly volatile, it can form high vapor pressure in the fuel rail. When this pressure exceeds the fuel system's pressure, vapor lock occurs, resulting in overly lean fuel vapor being injected and causing difficulty in starting; 4. Engine carbon buildup: Excessive carbon deposits on intake valves, throttle bodies, or pistons can absorb fuel, leading to an overly lean air-fuel mixture and affecting engine start-up.
I've been running an auto repair shop for many years and often encounter difficulties with hot starts, mainly due to fuel system issues or electrical faults. The most common problem is fuel vapor lock—when the engine is hot, the fuel evaporates and gets trapped in the fuel lines, preventing fuel from reaching the engine and causing ignition failure. The crankshaft position sensor is also prone to issues when hot; thermal expansion can lead to poor contact, disrupting the engine control unit. Another culprit is the fuel pump relay, which can fail when the switch sticks due to high temperatures. I remember one customer who couldn't restart their car after parking in the summer—it turned out the relay was faulty. Hot-start issues are troublesome and, if left unresolved, can even damage the ignition coil. It's best to inspect the fuel system and sensor connections every six months to prevent problems. Always seek professional repair promptly to avoid minor issues escalating into safety hazards.
