What is the reason for the abnormal noise from the transmission when the car is cold and the noise disappears after the car warms up?
3 Answers
The reason for the abnormal noise when the car is cold and the noise disappears after warming up is: when the car is cold, due to gravity, the engine oil is all in the oil pan and has not yet fully lubricated all parts of the engine. At this time, when starting the engine, there is no oil film between the components, especially in areas such as the cylinder head and valves. Without lubrication, abnormal noises will occur. After the car warms up, all parts are fully lubricated by the engine oil, and the noise will disappear. Reasons for the abnormal noise: noise caused by valve knocking; noise caused by the generator belt being too tight or too hard; noise caused by the generator belt slipping; noise caused by the timing chain loosening. Solutions: First, check whether there are any unfixed, easily rolling, and noise-making objects placed in the trunk or rear seats to eliminate noise caused by improperly secured items. Some abnormal noises can even predict potential serious damage to the engine. Therefore, when abnormal noises occur in the engine, they should be repaired promptly to prevent the fault from worsening. In addition to tightening screws, placing cardboard-like materials at the noise source can easily eliminate the abnormal noise.
There are two main reasons why the transmission makes abnormal noises when the car is cold but disappears after warming up: First, the viscosity of the transmission oil changes with temperature. At low temperatures, the oil is thicker and flows slower, leading to insufficient lubrication of internal components such as gears or bearings, which causes noise during friction. When the car warms up, the oil thins and lubrication improves, eliminating the noise. Another reason is the thermal expansion and contraction effect: when the car is cold, metal components contract, causing gaps between parts to increase or decrease, which may lead to rattling noises. After warming up, the components expand, and the gaps return to normal. I've seen this phenomenon in some models, especially older cars with deteriorated oil quality or worn gaps. It is recommended to check the transmission oil level and quality and replace it promptly to prevent more serious faults from long-term use. If the noise worsens or is accompanied by other symptoms, seek repair immediately, as ignoring it may increase repair costs and driving risks. Regular maintenance is key, and switching to a lower-viscosity oil before winter can help reduce the occurrence of this issue.
I've encountered a similar situation: the transmission makes a clunking noise during cold starts, but quiets down after driving for a few minutes. The mechanic said it's caused by thick oil providing insufficient lubrication, leading to component friction. This is quite common and nothing to worry too much about, but you should monitor the noise level. If the frequency increases or the sound becomes louder, it might indicate internal wear like a damaged synchronizer ring; I once solved it simply by changing the oil. Experience has taught me that warming up the car for 5-10 minutes before driving in cold weather can reduce abnormal noises and extend its lifespan. Long-term neglect can accelerate component wear, making repairs expensive and troublesome. A simple fluid check can prevent future issues.
