Bought a 2008 impreza with 116k miles for grandson in Feb. Head gaskets, timing belt and water pump were done prior to purchase. Last week, cylinder 4 misfire, then car wouldn't start. Towed to garage and my mechanic changed plugs and wires. Said no longer skipping. Coolant low so replaced. Said car was good to go. Grandson picked up car, after an hr started overheating. My son took it for a ride m, running no ac to confirm yes it is overheating Brought back to garage. Been there 3 days as mechanic can't say for sure what's going on. He keeps going back to head gaskets but not positive. Last update, car ran at idle for 3-4 hrs not overheating. Does have bubbles in coolant system. Engine skips when cold.