Mechanic Q: What would cause the Engine to lock-up suddenly??

Starter has been ruled out as a possibility also engine oit has been recently changed and is still full and clean tried to force turn the engine with wrench on p/s pump but no movement at all in either direction. Help!!!

Q: My engine suddenly locked up at idle and in drive any ideas will be greatly appreciated.?

the truck has a 3.0 Ltr V6 with 179,000.00+ miles on it and has had the oil changed recently the oil is full and clean this is not the overhead valve version so no timing belts