High-mileage engines: should you change oil strategy?
Past 120,000 miles the priorities shift, but not as far as the marketing suggests.
Stay with the specification
A worn engine still has the clearances and oil passages it was built with. The approval requirement does not change with mileage, and a DPF does not become tolerant of ash because the car is old.
Where high-mileage oils help
They carry more seal conditioners and slightly higher viscosity within the same grade, which can slow a minor leak and quieten an engine that has started using oil. They do not repair anything, and they are not a substitute for finding the leak.
Shorten the interval instead
The single most useful change on a high-mileage engine is more frequent oil changes at the correct specification. Contaminants build up faster in a worn engine, and fresh oil removes them.
Know when it is not the oil
Rising oil level, coolant loss, blue smoke or a mayonnaise-like residue under the filler cap all point at mechanical problems that a different oil will not address.
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