BUY WITH CARE

The 2AZ-FE's cylinder-head bolts thread directly into the aluminum block, and those threads strip or pull out. 33 federal complaints across these windows -- most on the 2004-2007 Highlander, where it is the engine's signature failure -- describe head-bolt threads stripping, head bolts pulling out, a resulting head-gasket leak, coolant loss (sometimes into the cylinders) and overheating. Owners are typically told the only fix is a new or rebuilt engine, often just outside warranty. The complaints skew four-cylinder wherever cylinder count is recorded, so this is the 2.4L four's failure, not the V6's.

Check — On a cold engine check the coolant level and condition, look for unexplained coolant loss with no external leak, white or sweet-smelling exhaust, and any history of overheating or head-gasket work. A documented head-bolt/thread or head-gasket repair (or engine replacement) is reassuring; unexplained coolant loss or overheating on a 2.4L example is a walk-away.