I'm reporting on my successful installation of an engine block heater on a 4 cylinder 2005 Tacoma - for the benefit of future searchers of the archives.
Toyota of Canada Part #00213-02141, available in the USA from trdparts4u.com for $60.
Installation method used:
1. Put front of truck up on jackstands and drained coolant.
2. Removed front passenger wheel to get a little wiggle room and a better view of workspace.
3. Got underneath truck (making sure it's well-supported first!).
4. Located oil filter on passenger side.
5. Looked directly behind the oil filter at the engine block. There's a freeze plug right there. (There's another freeze plug about 6" further towards the firewall, rearward from the filter. Don't use that one, tempting as it may be. There isn't enough room inside the coolant passage for the heater to fit there.)
6. Removed the freeze plug using my preferred method. I used a punch and 2lb hammer. Just hit the plug off-center a few times and it budged. Then I pulled it out with a set of pliers. Cleaned up the hole with 1000 grit sandpaper.
7. Retrieved block heater. Lubed the o-ring with the provided silicone. Pressed the heater firmly and evenly into the freeze plug hole. Made sure the o-ring was seated properly.
8. Tightened the screw on the outside of the heater to 19 inch-lbs per instructions. The heater felt nice and snug.
9. I routed the power cord to the lower air dam.
10. Then added coolant back to the system, ran the engine, and checked the heater for leaks (visual inspection). No leaks!
11. Put the wheel back on, lowered the truck and drove around for a week. Still no leaks.
Other important stuff: The instructions that come with the heater were last revised in 1995. They're helpful for a '94-'95 Tacoma, but not so useful for us. Nonetheless this part is still recommended for Gen2 trucks by Toyota Canada. Also, make sure you pick the correct freeze plug hole. If not, you'll be special-ordering a replacement freeze plug from Toyota! Also, V6 guys: your block heater is a totally different design that plugs into the rear of the block. And, luckily for you, installation does not involve draining coolant.