What causes the rattling noise when starting a 2009 Highlander?
1 Answers
If a 2009 Highlander makes abnormal noises during startup, it indicates that the hydraulic lifters are worn or there is a system pressure leak. If the lubrication system pressure is insufficient or the hydraulic lifters are severely worn, the pressure inside the hydraulic lifters will not be enough to support the plunger, leading to increased valve clearance. This results in a "ticking" sound from the valve impact during engine operation. Additional details are as follows: 1. Most modern car engines use hydraulic lifters: Hydraulic lifters are a component of the engine's valve train, typically installed on the cylinder head. Their function is to open and close the valves under the drive of the camshaft while automatically adjusting the valve clearance to maintain zero clearance. This helps reduce impact, lower noise, and extend the lifespan of components. 2. Reasons for the "ticking" sound in the car: Under normal conditions, hydraulic lifters are always filled with oil at a certain pressure to ensure zero valve clearance, preventing valve noise during operation. However, if the lubrication system pressure is insufficient or the hydraulic lifters are severely worn, the pressure inside the lifters cannot support the plunger, increasing the valve clearance. This causes a "ticking" sound from the valve impact during engine operation. Particularly with severely worn hydraulic lifters, if the car is parked for an extended period, the oil inside the lifters may leak out, leading to a "clicking" sound from the valve stem impact.
