Possible Connections (Less Likely but Worth Investigating):
* Coolant Loss & Overheating: A blown heater core leads to significant coolant loss. Severe overheating can cause:
* Head gasket failure: This is a major problem. Overheating can warp the head or crack the head gasket, leading to coolant mixing with oil (milky oil), loss of compression, and knocking.
* Rod knock: Extreme overheating can cause connecting rod bearings to seize, resulting in a loud knocking sound and lack of power. This is usually catastrophic engine damage.
* Piston damage: Similar to rod knock, extreme overheating can damage pistons.
* Air in the Cooling System: After a heater core replacement (or even a major leak), air can get trapped in the cooling system. This can cause overheating in localized areas and lead to knocking if a part gets too hot. Proper bleeding of the cooling system is crucial after a repair.
Possible Unrelated Problems (More Likely):
* Ignition System Issues: Knocking *could* be detonation (pre-ignition) from an issue with timing, spark plugs, ignition wires, or the distributor. Lack of power points towards a possible ignition problem as well.
* Fuel System Problems: A clogged fuel filter, faulty fuel pump, or problems with fuel injectors could lead to lack of power. This wouldn't directly cause knocking, but the engine running lean could.
* Mechanical Issues (unrelated to overheating):
* Connecting rod bearing failure (not necessarily due to heat): These can fail regardless of overheating due to wear and tear or lack of lubrication.
* Valvetrain issues: Problems with the valves, lifters, or rocker arms could cause knocking and power loss.
Troubleshooting Steps:
1. Check the Oil: Is it milky or discolored? This indicates coolant mixing with oil, a strong sign of a head gasket failure. Check the oil level; low oil can also cause knocking.
2. Check the Coolant Level: Make sure the coolant level is correct and that there are no leaks other than the (now repaired) heater core.
3. Listen Carefully to the Knock: Is it a consistent knock, or does it change with engine speed? A high-pitched knock might suggest a valvetrain issue, while a deeper knock is more suggestive of a rod bearing or piston problem.
4. Inspect the Spark Plugs: Are they fouled, worn, or damaged?
5. Check Fuel Pressure: Use a fuel pressure gauge to check if the fuel pressure is within the manufacturer's specifications.
6. Inspect the Ignition System: Check the distributor cap, rotor, spark plug wires, and ignition coil for damage or wear.
Recommendation:
Given the severity of the symptoms (knocking and power loss), it's highly recommended that you take your Skylark to a qualified mechanic for diagnosis. Attempting further troubleshooting without proper tools and experience could lead to more significant engine damage. The sooner you get it checked, the better the chances of a less costly repair. Ignoring a knocking engine is dangerous and likely to lead to catastrophic engine failure.
