Why is it difficult to start a cold car but normal when the engine is warm?
2 Answers
Difficulty starting a cold car but normal when the engine is warm may be due to a faulty coolant temperature sensor, causing the ECU to use preset values stored in its memory. Here are some solutions for cold start difficulties: 1. Low engine temperature: The temperature inside the engine is insufficient, and both fuel and lubricating oil are not warm enough. Therefore, more fuel should be injected during a cold start to meet power requirements. Poor fuel atomization at low temperatures leads to reduced ignition energy, affecting performance and causing the car to shake. Aging ignition coils, spark plug high-voltage wires, or electrical leakage can also result in decreased ignition energy. 2. Excessive carbon buildup on valves and intake passages: Carbon deposits can absorb an appropriate amount of fuel, causing the ECU to make incorrect judgments. For example, if the ECU controls the injection of 100 units of fuel-air mixture, but only 90 units actually enter the cylinder (with 10 units absorbed by carbon deposits), even if the remaining 90 units burn completely, the required power output may not be achieved, inevitably leading to shaking.
I've been driving for over thirty years, and the most common issue with hard cold starts but normal hot starts is an aging battery. At low temperatures, the internal resistance of the battery increases, its discharge capacity weakens, and the voltage drops during ignition, making the engine struggle to turn over. Additionally, engine oil is more viscous when cold, leading to poorer lubrication and increased starting resistance. If the car starts fine when warm, it means the overall electrical system is intact and the starter isn’t faulty. Check if the battery is over three years old—use a multimeter to measure the voltage; if it’s below 12 volts, replace it immediately. Using synthetic oil like 5W-30 significantly improves flowability in winter. Avoid frequent short trips in daily driving; aim for at least half an hour per drive to allow the alternator to fully charge the battery. Pay extra attention to battery health during summer maintenance to prevent this issue.
