Ford Repair: should i replace my engine, backyard mechanic, oil gauge

Question
I have a 1998 ford explorer,it just recently started making a nose thats sounds like a diesiel truck and today the oil gage started flickering real fast back and forth.I took it to a machanic and they told me its something inside making the nose,but they can't pinpoint it without taking it apart ,he said if it was him he would look in to replacing the engine completely,so my question to you is do i put a new engine in,and what should something like that cost?or do i tear the engine apart and see if it can be fixed.I also had a backyard mechanic say he thought it could be an engine rod,im so confused i don't know who to listen to please help:)

Answer
Katrina, I cannot assess your question without getting more specific detail of the problem.  The oil gauge moving, is not a defintive reason for engine problems.  The only way to find out is to have the mechanic do a cylinder compression test, then check if you have black smoke coming out from the exhaust, then check if you have oil spitting from the muffler or on the ground.  If some or all of these things are happening, then you may have an engine problem.  I would have check the cylinder head, as you might have a stock valve, instead of a bad engine.  I have tried to give you clues as to what questions to ask, before your commit to a new engine.