Chrysler PowerTech 4.7 V8

Chrysler's 4.7-litre V8 — the PowerTech, fitted to the Grand Cherokee, Dakota, Durango and Ram before the HEMI displaced it from the top of the range and the Pentastar replaced it from below.

It is a single-overhead-cam design with a reputation that is genuinely mixed, and the reason is specific: it is intolerant of overheating and of extended oil intervals. Sludge from neglected servicing blocks the oil passages, and the resulting camshaft and bearing wear is the usual cause of the knocking that ends these engines. A 4.7 with unknown service history is a compression and oil-condition inspection before anything else.

The second known issue is head gasket failure following an overheat, which on this engine tends to be terminal rather than repairable because the aluminium heads warp readily. Where the engine has been maintained on schedule and never overheated, it is unremarkable — which is why owner history matters more here than mileage does.