Hmm, okay, if its ahead if the middle line, and doesn't come back as it should since you have a T-stat valve, its overheating. Yeah, get that serviced and fill it will about 2 liters of coolant and rest distilled water. I also have a mehran, but donot have a t-stat valve, didn't have it from the showroom, but I let my temp gauge stay at the middle, my fan is automatic, and yet it never goes beyond the half line even with AC. And I always rev high, change the gears late within the limit of course.. its just so much fun even in a mehran