there are two types of civilian radar. One relies on the plane telling the "radar" where it is and the other is a true RAdio Direction And Ranging system that sends a radio pulse out and listens for the reflected signal to come back giving it a range and direction. To avoid clutter on the screens, control towers only tend to use the first one but military use both as the enemy is unlikely to sqwark their location to you.
The +4 hours thing on the engine data seems to be a bit vague at the moment. One minute they are saying that they have it, the next they don't. Rolls Royce don't seem to have made a statement yet about it but the US are now searching the Indian Ocean so there is possibly some truth in it.