It is the combination of living and mechanical components that makes them cyborgs. The outer-tissue is also interactive with the endoskeleton inside. As the Terminator from Terminator 2 says: “I sense injuries. The data could be called pain.” Implying a bio-mechanical feedback from the skin to the CPU.
The Terminators are also always called cybernetic organisms.
From the movie transcripts:
Terminator 1: Reese: Not a robot. A cyborg - cybernetic organism.
Terminator 2: T-8xx: I'm a cybernetic organism. Living tissue over a metal endoskeleton.
Terminator 3: T-8xx: T-X is designed to terminate other cybernetic organisms.
Terminators that would be considered cyborgs would be:
- T-8xx series.
- Marcus Wright (T-RIP / T-700 / Hybrid Models)
- Cameron Phillips (series TOK715?)
Cameron Phillips (from the Sarah Connor Chronicles) is the only Terminator to ever be shown to eat something. She also had functioning tearducts, and can feel heat and wind on her skin.
While they have blood and skin it isn't the same as normal human tissue. In the Sarah Connor Chronicles and Terminator Salvation there is a comment that the Terminator's flesh heals at a much quicker rate than normal humans. Cromartie is also shown to have procured eyes from a living person. He was not able to artificially make eyes for his outer-layer.
In contrast the following Terminators are not considered to be cyborgs:
- T-1000 / T-1001