THE TICK-This is a question that has been tossed around more than a mixed salad. The popular rumor is that the blue stripe means that the head was replaced by the dealer (or at the factory) to fix the tick issue. First, some facts. The tick issue can occur on any 2003 or 2004 Cobra, and also Mach 1s. The latest head, and the one that fixed the tick issue, wasn’t released until 01/2005. Second, the blue stripe has appeared on 2003 and 2004 Cobras/Mach 1s from the factory. It has appeared on both the driver side and passenger side heads. So it has no correlation to the fix issue that we’re are definitely aware of. However, since some 2004 Cobras have reported to have 9 spark plug threads (only head that is known to have 9 threads is the latest head), it is possible that the head part number is the latest head. This hasn’t been proven yet.
As far as what the blue stripe means, JB from SVTPerformance.com belongs to a local Cobra club and they toured the factory a couple of years ago. This was the explanation given at the factory. “
ssembly plants use just-in-time inventory, meaning parts are not stored up but are delivered daily. The paint markers provide a visual confirmation of when particular batches have been purged from the line. They show up on other Ford engines besides the ’03/’04 Cobra. The bottom-line is that the blue stripe doesn’t mean a head has been replaced by a dealer”.
Here is great site for Cobra info- Terminator FAQs