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There are a couple of things that can seize an engine but disassembly and inspection are needed to prove this.
First, Make certain the engine is actually seized by removing the serpentine belt, put a socket and wrench on the front crank shaft bolt and confirm it will not turn.
Ways it can seize.
1) No oil in engine - Last place that changed it forgot to put oil in or it has leaked out
2) Blown head gasket can cause "Hydro-Lock": the cylinder fills with coolant and can not turn over.
3) manufacturer defect - bolts internally were not tightened properly
4) Starter - starter is hung or damaged blocking the flywheel from turning
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