Owner's Problem Description
The owner reports a very loud vibrating and grinding sound from the Saturn SL2, suggesting a possible issue with the power steering pump. However, the noise does not change with pump load. The sound seems to be centered over the timing belt cover and is louder when the engine is cold, varying with engine speed but unaffected by AC or alternator load. The owner is concerned about possible implications of this noise.
Professional Technical Analysis
The vehicle in question is a 1999 Saturn SL2, equipped with a 1.9L 4-cylinder engine and an automatic transmission, typically seen with around 150,000 miles on the odometer. The symptom described—a loud vibrating and grinding noise—indicates potential failure in a belt-driven component. Despite initial thoughts of the power steering pump, the fact that the noise is unaffected by load suggests a different source. The timing cover area is suspect, particularly as the noise is accentuated when cold and correlates with engine speed, indicating a mechanical issue rather than an electrical one. Given the age of the vehicle, common failure points could include the water pump, tensioner, or other pulleys. A careful examination of the timing chain and its tensioners is warranted, as Saturn models of this era are known for timing chain issues. A comprehensive diagnostic approach, including belt removal to isolate the noise source, will be necessary for accurate diagnosis, especially considering the absence of load effect from the AC and alternator. Immediate attention to this noise is recommended, as it could indicate failing bearings or other critical component degradation.
Possible Causes
Most common causes (ordered by frequency):
- Water Pump Bearing Failure: The water pump, which is driven by the engine belt, can develop a bearing failure leading to a grinding noise. When the engine is cold, the lubricant may not flow adequately, causing increased friction and noise. A typical failure symptom is noise that increases with engine speed. The pump should be inspected for play in the shaft and proper sealing. Replacement cost for the water pump typically ranges from $100 to $200 with labor estimated at 2-3 hours. - Loud grinding noise from the timing cover area, increasing with engine speed, significant play in the water pump shaft during inspection.
- Timing Chain Tensioner Failure: The timing chain on the Saturn SL2 is known for potential issues, especially with the tensioner. If the tensioner fails, it can lead to chain slack, resulting in a grinding or rattling noise that varies with engine speed. Symptoms usually include noise when cold, which indicates inadequate tension and potential wear or damage to the timing chain itself. Repair costs can range from $500 to $800 depending on parts and labor. - Rattling noise from the timing chain cover area, increased noise when cold, visual inspection shows tensioner wear and chain slack.
- Damaged Accessory Pulley Bearings: Other belt-driven components, such as the alternator or AC compressor, may have failing bearings, causing a grinding noise. This noise is typically proportional to engine speed and may change under load, but in this case, it remains constant regardless of AC or alternator operation. Inspection should include checking for play in the bearings and noise while spinning the pulleys by hand. Replacement costs for the alternator or other accessories can vary widely, typically ranging from $150 to $400. - Grinding noise remains constant regardless of AC or alternator load, inspection reveals bearing play in the alternator pulley.
- Belt Tensioner Noise: The belt tensioner itself may be failing, leading to improper belt tension and resulting in noise that can be mistaken for other components. A failing tensioner may produce a squealing or grinding noise that increases with engine speed. This is often accompanied by visible wear on the tensioner pulley. Replacement costs typically range from $100 to $250. - Increased noise correlating with engine speed, visible wear and damage on the tensioner assembly during inspection.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Visual Inspection: Start with a thorough visual inspection of the engine bay, focusing on the timing chain cover and surrounding components. Look for signs of wear or damage to the water pump, tensioner, and accessory pulleys. Check for any loose or damaged belts. This initial check can often reveal obvious problems.
- STEP 2 - Belt Removal for Isolation: Remove the serpentine belt to isolate the water pump and other belt-driven components. With the belt removed, start the engine briefly to determine if the noise persists. If the noise disappears, the source is likely one of the removed components. If the noise continues, further investigation of the timing chain and tensioners is required.
- STEP 3 - Component Testing: Test the water pump and tensioner for proper operation. Check for play in the water pump shaft and tensioner bearings. Use a stethoscope or similar device to listen for abnormal noises while the engine is running. Document findings and compare with specifications for acceptable play and noise levels.
- STEP 4 - Road Test: After isolating the noise source, perform a controlled road test while monitoring the engine performance closely. Listen for any changes in noise level during acceleration and deceleration, noting any correlation with engine speed and load conditions. This can help confirm the diagnosis made during prior steps.
