1. Identify the Cause (Crucial First Step):
* Low Oil: This is the most common culprit. Check the oil level. If low, or if the oil is milky (indicating water contamination), you might have serious internal damage. Don't attempt to crank the engine until you address this.
* Seized Bearings: Lack of oil or water contamination can seize bearings, preventing rotation. This is often accompanied by knocking sounds before lockup.
* Broken Rod/Connecting Rod: A catastrophic failure can leave a connecting rod jammed against the block. This requires significant engine repair.
* Hydrolocked Engine: Water in the cylinders from a cracked head gasket or excessive moisture ingress can prevent rotation.
* Broken Piston(s): A broken piston can jam the crankshaft.
* Other Internal Damage: Many other possibilities exist, including damaged valves or camshaft issues.
2. Initial Checks (Before Attempting to Turn the Engine):
* Check the Transmission: Make sure the transmission is in neutral or park (automatic). A stuck transmission can also resist engine rotation.
* Battery: Ensure you have a fully charged battery to provide enough power for any attempts to turn the engine. A weak battery will not help and might damage the starter motor further.
* Starter Motor: Make sure the starter is functioning correctly. A weak or damaged starter can struggle even with a free engine.
3. Attempts to Free the Engine (Proceed with Caution):
* Manual Rotation (If possible): On some engines, you might be able to use a wrench on the crankshaft pulley or harmonic balancer bolt to manually rotate the engine. Try turning it in both directions, feeling for resistance points. Do this VERY slowly and carefully; forcing it can cause damage.
* Penetrating Oil: Apply a high-quality penetrating oil (like PB Blaster or Liquid Wrench) to the crankshaft pulley, the spark plug holes (allowing it to penetrate into the cylinders), and anywhere else accessible. Allow it to soak for several hours or even overnight. This helps loosen any rust or corrosion. Repeat applications may be necessary.
* Tow Starting (Extreme Caution): Only attempt this as a LAST RESORT if you've ruled out other causes and are comfortable with the potential risks. This involves having someone tow the car very slowly while you attempt to engage the starter. Incorrectly done, this can cause serious damage.
4. If the Engine Still Won't Turn:
You'll need professional help. Continuing to force the engine could result in catastrophic failure, requiring expensive engine rebuilding or replacement. A mechanic can diagnose the problem properly and determine the best course of action. They have specialized tools to help assess the extent of the damage.
Important Considerations:
* Safety First: Always disconnect the negative battery terminal before working on the engine. Wear appropriate safety glasses and gloves.
* Professional Help: If you're not mechanically inclined, don't attempt major repairs yourself. The potential for costly damage is substantial.
A locked-up engine is a serious issue. A professional assessment is usually the most cost-effective and safest approach in the long run.
