Can a bad timing belt change lower fuel efficiency?

I recently had my timing belt and water pump replaced on a 1992 Subaru Legacy AWD wagon (184,xxx miles). My mechanic also cleaned out the radiator and replaced the thermostat, spark plugs, spark plug wires, flushed the coolant, and changed the oil. Since I got the car back, it is making a squeeling sound when it starts up and, worst of all, my mileage has dropped from 25-27 mpg to 19-20 mpg. Any ideas???

One cause - incorrect camshaft timing. That would explain mpg loss, but not the squealing.

The squealing is likely an engine belt that either wasn’t tightened enough or the tensioner is faulty.

To add to the prior messages, the timing could be off or the thermostat could be defective, causing the engine to run cold.