If
you need a new pressure cap to use on expansion tank on your Sonett V4 you may have found that it is difficult to find a suitable one. To find one that keeps the system pressurised and then opens at the approriate pressure can be a hassle. The best option seems to be the Stant 10205 radiator cap.
http://www.saabnet.com/tsn/bb/sonett/index.html?bID=3909
