* Specific Engine: Even within the same family of engines (like a 3.4L V6), there can be significant differences between years. Internal components, mounting points, and even the computer systems can vary.
* Model Year of the Vehicle: The engine bay design and associated parts (wiring harness, mounts, etc.) are specific to each year and model of 4Runner or truck. A later-year engine might not fit into an older vehicle's engine bay without significant modification.
* Transmission Compatibility: The transmission must be compatible with the engine. Even if the engine fits, the transmission might not.
* Computer Systems (ECU): Modern engines rely heavily on electronic control units (ECUs). Swapping an engine might require significant wiring modifications or a complete ECU swap, which can be complex.
To determine interchangeability for a *specific* swap:
1. Identify the exact engine code (e.g., 3RZ-FE, 5VZ-FE, 1GR-FE) for both the donor and recipient vehicles.
2. Research online forums specific to Toyota 4Runners and trucks (like TacomaWorld, Yotatech). These forums have detailed information from people who have performed these swaps.
3. Consult a Toyota parts catalog or a reputable mechanic specializing in Toyotas. This is the most accurate way to determine compatibility.
General Guidelines (with significant caveats):
Engines within the *same generation* often have *better* chances of being swappable, but still require careful consideration of the above points. For example, 3RZ-FE engines across several years might share more commonality than a 3RZ-FE and a 1GR-FE.
In short: Don't assume interchangeability. Thorough research and professional advice are crucial before attempting an engine swap.
