What Are the Reasons for Valve Noise When Cold but Not When Hot?
3 Answers
The reasons for valve noise when cold but not when hot include unsuitable oil viscosity, low oil pressure, and poor sealing of the hydraulic tappet itself. Unsuitable oil viscosity: If the oil viscosity is inappropriate, especially during cold starts in the morning, air can enter the hydraulic tappet, causing abnormal noise. Low oil pressure: This is due to faults in the car itself, such as issues with the oil pressure relief valve or oil pressure sensor, which result in low oil pressure. This leads to oil leakage in the hydraulic tappet and air ingress, ultimately causing abnormal noise. Poor sealing of the hydraulic tappet itself: There are two reasons for poor sealing. One is wear on the hydraulic tappet itself, and the other is the cooling of the car after being parked for a while. The hydraulic tappet shrinks due to thermal contraction, leading to poor sealing and air ingress. Solutions: Clean carbon deposits and check the oil. Cleaning carbon deposits: Cleaning the carbon deposits helps because, during a cold start, the oil pump cannot immediately establish oil pressure, and oil films cannot form between components. This is especially true for the valves in the cylinder head (upper part), which do not get lubricated during a cold start. Whether it's hydraulic lifters or mechanical rocker arms, there will be some valve clearance, leading to abnormal noise. Check if the oil level is low, then measure the oil pressure. Valve noise when cold but not when hot could be the sound of piston slap or hydraulic tappet noise. It is recommended to clean the engine during the next car maintenance.
Our mechanic friends all know that when a cold engine starts, the valves make noise but become quiet once the engine warms up. This is mostly due to issues with valve clearance. When the engine is cold, metal components contract, increasing the gap between the camshaft and valves, resulting in a clattering sound during operation. After the engine warms up, thermal expansion fills the gap, naturally eliminating the noise. Another common factor is the high viscosity and slow flow of engine oil at low temperatures, preventing the hydraulic lifters from filling up in time, leading to insufficient lubrication and noise. I’ve seen many older cars like this, where owners neglect regular valve clearance adjustments or oil changes, accelerating component wear. It’s advisable to listen for noises during cold starts each week and promptly check the clearance or switch to low-viscosity full synthetic oil for effective prevention. If the noise persists, visit a professional shop early to adjust the valves or replace the lifters—after all, it affects the engine’s lifespan.
After playing with cars for a long time, I've figured this out. The root cause of valve noise when cold and silence when hot lies in thermal expansion/contraction and lubrication issues. Engine components are made of different materials—aluminum cylinder heads contract more than iron valves when cold, creating larger gaps that allow cam lobes to tap and generate noise. When warmed up, everything expands and fits snugly, eliminating the sound. Meanwhile, cold oil is thick like syrup, causing hydraulic lifters to operate with delay and produce noise. My car experienced this; switching to more fluid 5W-30 oil helped significantly. I also learned that insufficient oil pressure can cause lifter failure. Maintenance-wise, regular oil changes are key—once the engine reaches operating temperature, the noise becomes rare. Remember, don't wait until the noise gets severe; checking valve adjustments can save you from major repairs.
