Yes, as a few already said, your motor is just hydra-locked. You say it wasn't hot and was running fine when you shut it down then you will just need to have the heads checked and gaskets. Do not continue to try to start it until you can get the liquid out of the cylinders. Don't listen to all these people that know nothing about motors, you don't need a new motor! It's not going to be a cheap fix but it is very fixable and you will still have a great truck with a great motor that will run for a very long time. If I were you though, I would go ahead and put new injectors in it while it's torn down. Getting the heads checked and worked will take longer than the actual job itself.
IDK much about the D-maxes but I did do the injectors on my FIL's '03 and it had one injector that had a broken o-ring that was allowing oil into the cylinder. This could have caused the same condition on his if it had been bad enough but we were able to catch it in time. His truck smoked badly at idle but would clean up as soon as you gave it some throttle. Did or has your truck ever smoked (white/blue)?
