* Low Valve Lash/Insufficient Valve Adjustment (most likely): As the engine works harder uphill, the increased heat and pressure can cause slightly worn valve components to create more noise. The gap (lash) between the valve stem and the rocker arm (or tappet) might be too small. This gap is crucial for proper valve operation. When too small, the components can contact more forcefully under load, creating a clattering noise. This is exacerbated at higher engine speeds (40mph uphill).
* Worn Rocker Arms or Lifters: The rocker arms or hydraulic lifters (if equipped) could be worn, causing inconsistent contact with the valves. Increased engine load will magnify this wear and create more noticeable noise.
* Low Oil Pressure/Oil Viscosity: If your oil pressure is low, or if you're using oil that's too thin for the operating temperature, the lubrication of the valve train components could be compromised. The increased load uphill might exacerbate this insufficient lubrication, leading to increased valve noise. Old, dirty oil will also contribute to this.
* Sticky or Worn Valve Stem Seals: While less likely to be the sole cause of the noise, worn or sticky valve stem seals could contribute, especially under high loads.
Why only at higher loads and speeds? The noise is probably masked at lower speeds and flatter terrain because the engine's operating conditions are less demanding. The increased engine speed and strain on the valve train at higher loads and uphill reveals the existing wear or insufficient adjustment.
What to do:
1. Check your oil level and condition: Make sure your oil is at the correct level and isn't excessively dirty or showing signs of significant breakdown. Consider an oil change with the correct viscosity oil specified for your Windstar's engine and year.
2. Listen carefully to the noise: Try to pinpoint the location of the noise. This can help a mechanic diagnose the problem more accurately.
3. Get it inspected by a mechanic: A mechanic can properly diagnose the problem. They will likely check the valve lash/adjustment (or listen for lifter noise), examine the rocker arms and lifters (or check for low oil pressure), and inspect for other potential issues. This is especially crucial given that attempting valve adjustments yourself can be complex and potentially damage the engine if done improperly.
Ignoring the noise could lead to more serious engine damage, so it's best to have it checked promptly.
