Troubleshooting of Engine with Abnormal Noise During Cold Start

It is common for the vehicle to make abnormal noises during cold start, and for the sound to weaken or disappear after hot start. The deterioration of oil fluidity and changes in component clearances at low temperatures are the main causes. By investigating in order from shallow to deep, the source of the fault can be quickly located to avoid continuous damage to the engine.

1、 Priority inspection of lubrication system

The most common cause of cold start noise is delayed oil supply. Inconsistent oil viscosity grade, insufficient oil quantity, or oil pump pressure relief can cause friction due to component oil shortage during startup. At the same time, the oil filter is clogged, the oil circuit accumulates and releases pressure. After overnight, the oil passage is short of oil, and there will be a brief clicking sound during cold start. It is necessary to check the oil level and oil specifications, replace aged and deteriorated oil in a timely manner, verify the oil pump supply pressure, and eliminate metal noise caused by insufficient lubrication.

2、 Troubleshooting of Timing System Malfunctions

The typical manifestation of faults in the timing chain, belt, and tensioner is a cold car rattling noise. The low-temperature oil pressure of the hydraulic tensioner is slowly established, causing noise due to chain relaxation and guide rail friction; Long term use of the chain can lead to elongation and wear of the guide rail, and the abnormal noise will continue to worsen. In severe cases, there may be tooth jumping and damage to the valve. Observe the noise a few seconds before cold start, replace the aging tensioner, guide rail, and chain kit to prevent major mechanical failures.

3、 Abnormal noise in the clearance of the valve mechanism

Hydraulic tappet pressure relief is a frequent cause of cold car clattering sound. After the vehicle was parked overnight, the internal oil pressure of the strut was lost, and the cold start valve clearance was too large, causing a knocking sound. The abnormal noise disappeared when the oil pressure of the hot car was restored. In addition, regular noise may occur due to wear of valve rocker arms and camshaft pitting. Minor pressure relief can be relieved by replacing specialized oil, while severe wear requires disassembly and maintenance of valve components.

4、 External attachments and pin troubleshooting

After excluding internal mechanisms, check the pulley, tensioner, and water pump bearings. Insufficient lubrication of low-temperature bearings can cause sharp whistling. The engine mount rubber is aging and cracking, the rigidity of the cold car increases, and the vibration transmission forms a dull and abnormal noise, which is easily confused with the internal noise of the engine. By dismantling the accessory belts one by one for testing, the source of abnormal noise can be distinguished.

Cold start abnormal noise cannot be ignored. Long term neglect will exacerbate component wear. Troubleshooting in the order of lubrication, timing, valve distribution, and external accessories can efficiently lock in faults, complete repairs at a lower cost, and extend engine service life.