Toyota 1MZ-FE (MZ family, 2.5 and 3.0)

Toyota's 3.0 60° V6, in almost everything the company sold with six cylinders for a decade — Camry, Avalon, Sienna, Highlander, and the Lexus ES 300 and RX 300. 194 to 210 hp, the higher figure once VVT-i arrived in 1998.

It is the engine of the Toyota sludge affair, and that history is the first thing to establish about any example. Oil gelled in the engine rather than draining, and Toyota received 3,400 complaints by 2002, extended the warranty to eight years and unlimited miles, and settled a class action covering some 3.5 million Toyota and Lexus vehicles. The cars at risk are the 1997 to 2002 ones, and the settlement is long closed — so on a car bought today the question is not whether it is covered but whether it was ever cleaned.

What the sludge does is block the PCV system, and from there the symptoms read like several different faults: blue smoke, fouled plugs, and low compression concentrated in the rear bank, which is the harder one to reach and the one that runs hotter. Low compression on bank 2 alone, on this engine, is a sludge finding until proven otherwise rather than a worn-out engine.

On the VVT-i cars the actuator itself leaks or fails, which shakes at idle and takes power with it. Oil changes on time, with the right oil, are the whole of the prevention — which is an unsatisfying answer and the true one.