Why does the engine make a loud rattling noise during cold start?
3 Answers
Cold start engine rattling noise is loud because the engine oil flows back to the oil pan. During cold start, the oil pump cannot immediately establish oil pressure, and the internal valves do not receive sufficient lubrication, resulting in noticeable abnormal noise. During engine operation, the high temperature generated by the engine affects the valves and transmission components, causing certain expansion during operation, which tends to reduce the valve clearance. Cold start refers to starting the engine when the coolant temperature is low, usually after the car has not been started for a long time, such as after overnight parking.
With over 20 years of auto repair experience, I've found that engine rattling during cold starts is extremely common, especially in winter or low temperatures. The main cause is usually insufficient oil pressure inside the engine, where the hydraulic lifters fail to fill with oil promptly, resulting in excessive valve clearance and the characteristic noise. This issue is often oil-related: either the oil viscosity is too high or the oil has degraded, causing slow flow and inadequate lubrication when cold; a clogged oil filter can worsen this phenomenon. The solution is straightforward: replace with fresh oil using a low-temperature friendly grade like 0W-30 or 5W-30; allow 1-2 minutes of warm-up after starting to let the oil temperature rise before driving. Regular maintenance with oil changes every 5,000 km and using full synthetic oil can prevent this. Long-term neglect may lead to camshaft or valve wear, resulting in costly repairs. Car owners should pay attention to selecting season-appropriate oil and maintaining proper oil levels—it saves both money and hassle.
My car is an old SUV. Last winter, it made a loud ticking noise when starting, which really startled me. Later, I took it to the repair shop for inspection. The mechanic said the engine oil was too old and became thick like glue in the cold, preventing proper flow and causing noise in the lifter area. After changing to new oil, it immediately became quiet. Here’s my experience to share: use the viscosity oil recommended by the manufacturer; don’t rush to drive after starting—let it idle for a while to allow the oil to lubricate properly; check the oil every six months and don’t wait until the warning light comes on. Long-term noise like this can shorten the engine’s lifespan. For car owners in northern regions, 0W-series oil is more suitable. Maintaining the oil filter is also crucial to avoid impurities clogging the oil passages. After forming these habits, the car starts much quieter, and I feel more at ease on long trips.
