Chevrolet LA1

The 3.4 of GM's 60° pushrod V6 family — cast-iron block, aluminium heads, 170 to 185 hp — in the Impala, Monte Carlo, Venture, Grand Am, Aztek and Rendezvous. The larger sibling of the L82.

The fault this engine is known for is the intake manifold gasket, and it is a GM-wide one: the 1995–2004 cars with the 3.1, 3.4, 3.8 and 4.3 share a composite gasket that the metal either side of it works loose as the engine heats and cools, until coolant finds its way out — or worse, in. Coolant in the oil on one of these is the gasket until proven otherwise, and the revised gasket and thread-locked bolts are the repair rather than a head job.

Dex-Cool is blamed for it in most retellings. GM investigated and concluded the coolant was not the mechanism, and the honest reading is that the gasket fails on its own and the coolant then makes a visible mess of what it finds — which matters, because replacing the coolant and not the gasket fixes nothing.