How does oil aeration impact the effectiveness of hydraulic lifters in an engine?

Oil aeration, the presence of air bubbles within the engine oil, significantly reduces the effectiveness of hydraulic lifters. Hydraulic lifters, also known as hydraulic lash adjusters, maintain zero valve lash in an engine. They achieve this by using pressurized oil to fill an internal chamber, which compensates for wear in the valve train components. The oil acts as a hydraulic fluid, transmitting the force from the camshaft lobe to the valve stem. When oil becomes aerated, the air bubbles within the oil are compressible. Unlike oil, which is virtually incompressible, air bubbles compress under pressure. This compressibility interferes with the lifter's ability to maintain consistent valve lash. As the camshaft lobe pushes on the lifter, the air bubbles compress instead of transmitting the force directly to the valve. This results in a delayed or reduced valve opening, leading to decreased engine performance, particularly at higher RPMs. Furthermore, the compressible air bubbles can cause the lifters to become noisy. As the air bubbles compress and expand, they create a "spongy" effect, resulting in a ticking or tapping sound from the valve train. Severe aeration can lead to lifter collapse, where the lifter is unable to maintain contact with the valve train components. This can cause significant valve train damage. Common causes of oil aeration include low oil level, a faulty oil pump pickup tube allowing air to be drawn into the system, or excessive oil foaming due to oil contamination. For example, if the oil level is too low, the oil pump may suck in air along with the oil, leading to aeration and subsequent lifter malfunction.