While we hear of the TARDIS having engines that are implicitly essential to it working, we’ve also see a TARDIS work without the rest of the machine.
“The Doctor’s Wife” and “Inferno” show that a TARDIS is capable of operating as just the console, which would seem to imply that they’re just a power source to allow the console to do its thing and move the whole ship around, or to allow for the pilot to do silly things like tow an entire planet one second out of phase.
Given that dimensionally transcendental engineering is integral to TARDIS design, the engines - and pretty much all of the rest of the interior - could be inside the console - even if they are also accessible via other rooms and corridors.
And the console, like the TARDIS itself, could be bigger on the inside. So while we see a console, who knows what’s happening inside of it
Wow, this just blew my mind. I never thought about the TARDIS in quite this way kind of like a Russian nesting doll. I do recall in one episode with Tom Baker, Logopolis, the Doctor Jettisoned a significant part of the the TARDIS to escape a trap by the Master. This didn’t seem to compromise the TARDIS in any significant way. I always imagined the lost room could be easily replaced given a little time and effort.
My take, informed mainly by The Doctor’s Wife, is that while a TARDIS console alone can move through time and space, it’s a bit like driving a card without a windshield, exhaust system, shocks and brakes. It may get you where you’re going, but the odds of you experiencing harm increase greatly.
