The head gasket has a high failure rate due to cooling system problems. Subaru is aware of the problem and has extended the warranty to 8 years/100k miles on many vehicles.
Resources for the Repair and Maintenance of your 2001 Subaru Impreza Outback
2001 Subaru Impreza Outback
2001 Subaru Impreza Outback Problems
Front engine oil leaks can develop from the camshaft seal and the crankshaft front seal. If one or more seals require replacement, it may be wise to consider replacing the timing belt as well. These seals are commonly inspected and replaced as needed as part of a timing belt service.
The leak may develop from the oil pump seal. Our technicians prefer to use thread locker when replacing the seal to prevent the bolts from becoming loose again.
The Check Engine Light may illuminate because of a failed knock sensor. Although the sensor often tests okay, it can fail intermittently, while the vehicle is being driven.
A noise in the clutch called "clutch chatter" is common if the car is driven without allowing it to warm up.
2001 Subaru Impreza Outback Questions and Answers
Belts squeal on cold mornings till engine warms up. Can engine be damaged if belt breaks before I fix it?
Belt(s) squeal when starting car on cold days, goes away as engine warms. Can engine be harmed if belt bteaks while driving?