Only Red antifreeze type is suitable and you’ll need 8 liters of it. Make sure you service system at Peugeot with installed 1.1 engine correctly. For Peugeot 309 it’s important to have optimal antifreeze inside. In 1989 the company produced vehicles with 1.6 engine having code of B1A(XU51C). In other way 1988 309 won’t be used quite long and efficiently.
Better buy 8 liters of good antifreeze in Red color. 1.6 309 motors of 1993 year will serve more by optimal service. So better use Peugeot’s advice for servicing 1991 309. Every Peugeot owner should remember that engines with code K1D(TU3A) are quite demanding.