How much iron?
The first-generation Toyota Tundra’s 2UZ-FE is mostly an iron-block engine, but not an all-iron engine. The core piece people mean when they ask this is the cylinder block, and that block is cast iron; the cylinder heads are aluminum.
In plain terms, the engine’s heavy, structural part is iron, while the top end is lighter aluminum. That was a deliberate Toyota choice for durability and towing strength, even though it made the engine heavier than the all- aluminum UZ-family engines that came before it.
What is iron and what is not
- Cast-iron cylinder block: yes.
- Aluminum cylinder heads: yes.
- Crankcase, pistons, rods, and other internals: not fully specified in the sources here, so it is safer not to turn that into a percentage claim.
So if your question is, “How much of the 2UZ-FE is iron by the major engine casting?”, the answer is: the block is iron, but the engine is a mixed- material design, not a 100 percent iron engine.
The practical takeaway
For owners, the important point is that the 2UZ-FE’s cast-iron block is a big reason it earned a reputation for toughness in trucks and SUVs. That strength came at the cost of extra weight, which is why Toyota paired it with aluminum heads instead of making the whole engine iron.
If you were hoping for a precise iron percentage by mass, that is not something reliable sources commonly publish for this engine. What is well documented is the material split: iron block, aluminum heads.