Short answer: An engine overhaul means removing the engine, stripping it down, measuring the worn parts, and rebuilding it with new bearings, rings, gaskets and seals. It is worth it when the block and crankshaft are sound and the car is worth keeping.
Signs an engine may need an overhaul
High oil consumption, blue smoke from the exhaust, low compression on one or more cylinders, knocking from the bottom of the engine, metal particles in the oil, or coolant and oil mixing. Each of these can have smaller causes too, which is why diagnosis comes first.
What happens during an overhaul
The engine is removed and stripped to the bare block. The cylinder bores, pistons, rings, crankshaft, bearings, camshafts, valves and timing parts are cleaned, measured and checked against the maker's limits. Worn parts are replaced or machined, and the engine is reassembled with new gaskets and seals before going back in the car for testing.
Overhaul or a smaller repair?
A leaking gasket, a stretched timing chain or a failed head gasket can often be fixed without a full rebuild. A full overhaul makes sense when wear is spread across the engine, or when the engine is already apart and the extra work costs little more.
Overhaul or replacement engine?
Replacement can be quicker when a suitable engine is available, but its history is often unknown. An overhaul gives you an engine where every wearing part has been inspected. The right choice depends on the car's value, how long you plan to keep it, and parts availability.
Questions to ask your workshop
What did the inspection find? Which parts will be replaced and which reused? How will the engine be tested afterwards? A good workshop explains this clearly before you agree to the work.
