Rod Knock (Less Likely if Constant and Not at Startup): While rod knock is a classic knocking sound, it's usually present from the start and worsens as the engine warms. If it's only happening after the engine is warm, it's less likely, but still possible if the damage is progressing rapidly.
Main Bearing Knock (Less Likely if Constant and Not at Startup): Similar to rod knock, main bearing issues often manifest early. However, a developing problem could worsen with heat.
Piston Slap: This is a common cause of a knocking sound, especially in engines that have higher mileage or have experienced significant wear. Piston slap is often worse when the engine is cold and can lessen *or* worsen slightly as it warms up depending on the specific issue. If it’s worsening as the engine warms, the clearance is increasing, which is a bad sign.
Wrist Pin Knock: A worn or damaged wrist pin can cause a knocking sound that changes with engine temperature.
Connecting Rod Bearing Knock: These can sometimes start subtly and worsen with heat. Similar to the main bearing knock, this is less likely if the issue is *only* after the engine warms and is a constant sound.
Exhaust Manifold Leak: A leak in the exhaust manifold can create a knocking or ticking sound that might become more noticeable as the engine and manifold heat up.
Valvetrain Issues: A lifter that's sticking or failing could create a knocking sound that becomes more pronounced as the oil warms up. This is more of a tick or tapping than a deep knock, but can sound like a knock depending on the engine speed and the specific issue.
Loose or Worn Components: Something internally might be getting loose and knocking only once the engine's heat expands everything slightly. This is a very general possibility.
Pre-ignition or Detonation: While more of a pinging or rattling sound, severe pre-ignition can sound similar to knocking. This is influenced by things like fuel quality, timing, and compression. It's likely to happen under load.
To diagnose the problem:
* Listen carefully: Try to pinpoint the location of the knock. Is it from the top end (valvetrain) or the bottom end (crank/rods)?
* Check the oil: Look for metal particles in the oil.
* Inspect the exhaust manifold: Look for cracks or leaks.
* Consult a mechanic: This is crucial for accurate diagnosis, especially as you've noted it's a constant issue after warm-up. A mechanic can perform a compression test, leak-down test, and other diagnostics to determine the precise cause.
Ignoring a consistent knocking sound can lead to catastrophic engine failure. It's advisable to get it checked immediately.
