A knock under the hood is always a cause for concern. One of the common causes of extraneous noises is hydraulic lifters. These parts are located in the valve timing mechanism and are responsible for automatic adjustment of valve clearance. When the hydraulic lifter knocks, the engine becomes louder, with distinct metallic clicks audible. It is important to understand the reasons for this behavior and to know how to determine which hydraulic lifter is knocking in order to solve the problem in a timely manner.

Why the hydraulic lifter knocks when cold

Many drivers notice that it is in the morning or after a long period of inactivity that the hydraulic lifter knocks when cold. The reason lies in the fact that during the pause, oil drains from the internal cavities. After starting, the engine runs without lubrication for a few moments until pressure in the system rises. If the oil has thickened or lost its properties, the noise may last longer than usual.

Why the hydraulic lifter knocks when hot

Sometimes the extraneous sound appears in the opposite situation — the hydraulic lifter knocks when hot. In this case, the heated oil becomes too fluid and does not create the necessary pressure. Additional causes may be wear of the lifters themselves or clogging of their channels. This option is considered more dangerous because it indicates serious malfunctions that require inspection.

How the hydraulic lifter knocks

By the nature of the sound, one can roughly determine the nature of the malfunction. As a rule, the hydraulic lifter emits short metallic clicks that become more frequent as the RPM increases. Sometimes the sound disappears a minute after starting — for a cold engine this is considered normal. If the knocking persists longer or occurs on a warm unit, it is time to think about diagnostics.

How to determine which hydraulic lifter is knocking

Drivers are often interested in how to determine which hydraulic lifter is knocking. This can be done using a stethoscope or an ordinary screwdriver, applying it to the engine block. By the location and tone of the sound, it is possible to identify the faulty element. In service conditions, disassembly and oil pressure measurement are additionally used.

Volkswagen Polo hydraulic lifter knocking

Owners of imported cars are also familiar with this problem. For example, complaints are often heard that the Volkswagen Polo hydraulic lifter is knocking. Here the problem is usually related to the quality of the oil and compliance with its replacement intervals. For German engines, it is especially important to use the recommended viscosity and not to skimp on oil filters.

What to do if the hydraulic lifter knocks

If the hydraulic lifter knocks regularly, it is worth paying attention to the following points:
  • the level and condition of the oil in the engine;
  • the frequency of its renewal;
  • the serviceability of the oil pump;
  • the cleanliness of the lubrication system.
In some cases, flushing or switching to a higher quality oil helps. But if the wear is mechanical in nature, the only way out is to replace the damaged part.

Summary

Now you know why the hydraulic lifter knocks when cold and how to act when the hydraulic lifter knocks when hot. It is also useful to understand how the hydraulic lifter knocks and how to determine which hydraulic lifter is knocking in order not to waste time on unnecessary repairs. If such a sound appears in your car — whether it is a domestic model or a Volkswagen — do not delay the inspection. Timely correction of the malfunction will extend the engine's life and save you from serious costs.