Teardown Shows What It Takes to Kill Toyota's Most Reliable V-6

Toyota's 3.4-liter V-6 is known to last forever. But in this rare instance, catastrophe struck.

Photo by: YouTube

By: Brian Silvestro

Jan 11, 2025 at 1:00pm ET

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Toyota is well-known for building some of the most reliable engines on the planet. Perhaps its most stout powertrain is the automaker's VZ line of V-6s, first introduced in the late 1980s and used all the way up into the mid aughts. Over the years it's developed a reputation not only for reliability, but for being easy to service and cheap to run. But sometimes even the best can fail.

That's what happened to this engine. Acquired by the I Do Cars YouTube channel for a teardown, this 5VZ-FE is a rare example of a failed Toyota V-6. Host Eric claims he got it as a core trade, so it's not clear if the engine came from a 1996-2002 4Runner, a 1995-2004 Tacoma, or a 2000-2004 Tundra. Overseas, Toyota also used these engines in the Land Cruiser Prado, the Grand HiAce, and the Hilux.

First impressions are good. A peek under the valve covers reveals healthy camshafts, with only minor wear on the cam caps. There aren't any metal flakes or milky oil, just a bit of tarnishing on the aluminum. Removing the heads doesn't reveal any surprises either, with intact head gaskets.

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It's only when Eric goes to check the position of the last piston do things go awry. Instead of staying in place, it moves within the cylinder, indicating it's no longer attached to the crankshaft. Not good. Further digging reveals pieces of connecting rod strewn about the oil pan, separated from the piston. The loose pieces caused even more damage as they were flung around the crankcase, eventually punching a hole through the block.

Eric suspects a flooded cylinder is the culprit here. Seeing as how the head gasket was in good shape, he thinks a stuck injector dumped fuel into the cylinder, stopping the piston from being able to compress, leading to the carnage. With working replacements costing around $1,000, it's unlikely this engine will ever be rebuilt. Rest in peace.