One problem related to blown head gasket has been reported for the 2003 Ford Mustang. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2003 Ford Mustang based on all problems reported for the 2003 Mustang.
Purchased a 2003 Ford Mustang with 22,000 miles on it in Feb 2005. Had a ticking/tapping sound coming out of engine bay area at 30,720 miles. Took it to gervais Ford in MA, tech looked at it quickly out in the lot and said it was nothing to worry about but I could make an appointment if I would like to. Made an appointment the following week, had 2 tech's look at and they both said it was normal and not to worry about it. Well to my surprise at 37,000 miles 1,000 miles after the warranty has expired the engine fails. Took it back to gervais Ford and was told both head gaskets blew and it will cost me close to $2,000 to repair. Possibly more if any internal damage has been done. This is absolutely ridiculous on a vehicle that is new and the issue could have been possibly resolved earlier if that Ford dealer properly diagnosed the vehicle.