* Incorrect oil: Using the wrong viscosity or type of oil can lead to knocking. Check your owner's manual to ensure the correct oil was used and that it meets the manufacturer's specifications. Too thick an oil, especially in cold weather, is a common cause.
* Low oil level: Even a slightly low oil level can cause knocking. Double-check the dipstick to ensure the oil level is within the proper range.
* Contaminants in the oil: Though unlikely after a fresh oil change, if contaminants (e.g., debris from a failing engine part) were introduced during the oil change process itself, it could cause knocking.
* Timing issues: A problem with the ignition timing or valve timing can cause knocking. This could be coincidental with the services, or perhaps something was disturbed during the process.
* Pre-ignition or detonation: This is caused by fuel igniting too early, often due to high compression, too much heat, or poor-quality fuel. While a fuel system cleaning *should* alleviate this, if the issue was severe, it might not have been fully resolved.
* Damaged piston rings or bearings: Worn or damaged piston rings or bearings can lead to knocking. This is a more serious mechanical issue that would likely have been present before the oil change, but might be manifesting more strongly now if the old oil was masking the sound.
* Loose or damaged connecting rods: Similar to piston ring/bearing issues, a problem with the connecting rods is a major mechanical failure and will require professional attention.
What to do:
1. Check the oil level and type: Verify the oil level is correct and that the correct oil type and viscosity were used according to your owner's manual.
2. Listen carefully: Try to pinpoint where the knock is coming from (top end, bottom end). This can help diagnose the source.
3. Consult a mechanic: Given the persistence of the knock after servicing, professional inspection is crucial. A mechanic can diagnose the specific cause and recommend the appropriate repair. Don't continue driving with a knocking engine as it can lead to catastrophic engine failure.
It's important not to dismiss the knock. Continuing to drive with engine knock can lead to significant and costly damage.
