Chevrolet Iron Duke (L38 / LR8)

GM's 2.5-litre four — the Iron Duke — in the S-10 and Sonoma, and in a long list of GM cars before them.

Its name is the whole design brief: a cast-iron block and head at a time when everybody else was going to aluminium, pushrod-operated, slow-turning and built to survive neglect. It is one of the most durable engines GM ever made and one of the least pleasant, and both follow from the same decisions.

It is also famously rough, and that matters diagnostically: a four-cylinder with no balance shafts vibrates at idle as a matter of design, so an owner reporting shake is very often describing normal behaviour. Establish what changed before chasing a mount or a misfire.

What genuinely goes wrong is age rather than engineering. The distributor and its module fail and give a hot-restart stall that clears when cool — the classic symptom on these; the throttle body injection unit develops leaks around its base gasket; and the head gasket is a known item on high-mileage engines that have been overheated.

Parts are still common and cheap, which is usually what decides whether one of these is worth fixing.