Comprehensive Guide: How to Test if a Car Engine is Locked Up

Numerous rotating components within an engine facilitate its function, with engine oil providing essential lubrication for these parts. The oil filter plays a crucial role in purifying the oil. However, if the engine seizes or locks up, it necessitates either a complete engine replacement or a comprehensive rebuild.

Don't Be Fooled!

Certainly, there are situations where the engine may appear to be seized, but this isn't actually the issue. For example, if a front-mounted accessory like the AC compressor or alternator gets jammed, it can prevent the serpentine belt from moving, which in turn would stop the engine from turning over. Therefore, it's advisable to remove the serpentine belt before conducting any tests to determine if the engine is truly locked up.

What Goes Wrong?

  •  Lack of Engine Oil: An engine can seize for four primary reasons, with the most frequent being the depletion of engine oil. This deficiency results in the engine bearings losing their essential lubrication, leading to an overheating of the bearing material. Consequently, the crankshaft surfaces become galled, preventing the crankshaft from continuing to rotate. This scenario underscores the critical importance of regular oil changes and periodic checking of the engine oil level.
  •  Overheating: The cooling system is crucial for managing the engine's operating temperature, ensuring it functions efficiently. If there's a breach in the system or the thermostat malfunctions by remaining closed, the cooling process is disrupted. This deviation hinders the system's effectiveness, making the engine prone to operating at temperatures beyond its design parameters. Such overheating can lead to the expansion of pistons, causing them to jam against the cylinder walls and preventing the engine from turning.
  • Mechanical Failure: The piston connecting rod is the most frequent point of mechanical failure. This rod, vulnerable to breaking, can become jammed between the crankshaft and the engine block. While less typical, other failures can occur, including the crankshaft breaking or an issue with the exhaust or intake valve, where it might snap and fall into the combustion chamber.
  • Head Gasket Leak: The cylinder head gasket plays a crucial role in sealing the juncture between the cylinder head and the engine block. Its function extends beyond maintaining compression within the engine; it also prevents engine coolant from entering the combustion chamber. The intrusion of coolant into the chamber inhibits compression, resulting in engine seizure. If there's a possibility of such an issue, it's advisable to extract the spark plugs prior to conducting any diagnostic tests.

Here is What You Do

The goal involves reaching the front section of the engine, particularly focusing on the engine front pulley or balancer. It may be necessary to dismantle certain splash guards or shields to achieve this. You will find a prominent crankshaft bolt located at the center of the balancer, typically around 22mm in size. Your next step is to attach a socket to this bolt, and use a short extension if necessary, along with a breaker bar, essentially a substantial socket wrench.

The task requires you to manually rotate the engine in a clockwise direction, demanding a moderate amount of effort. If the engine does not turn as expected, an alternative approach is to try rotating it counterclockwise. This method can potentially overcome hydro lock resulting from coolant presence in the combustion chamber, or address issues like a snapped connecting rod.


This test is crucial when attempting to repair an engine that isn't starting. If there's a distinct thump sound while attempting to activate the starter, the engine might be seized. This evaluation is also beneficial when purchasing a pre-owned engine to ensure its functionality before installation.

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