DO THE TIMING CHAINS GO OUT OFTEN ON A 2008 MOUNTAINEER

The earlier build 4.0L V6 SOHC engine's like in your Mountaineer had issues with cam chain tensioners and chain guides. By 2008, this was not an issue so much, but certainly with tremendous amounts of mileage and time, they can wear and start to make noise. There is no "mileage interval" for replacement and they are expected to be installed for the life of the engine, so there is no recommendation other than to diagnose and repair as needed if a problem arises.