Lemme know when you find that bypass valve on ur Y2K XJ, I've been looking for one on mine for the past 9 years or so... Oh and how come none of you guys have tried using a slightly lower temp Tstat? I switched to a 180 unit, no hole drilled in it was the Napa brand and I did it when I had the old 0331 cylinder head replacement sage as a preventative measure, my heat comes on fine, nice and toasty and the temp hovers right around the 200 mark unless I'm on extended highway cruise when it seems to settle just a bit to the left of that, my MPG seems normal, no emmisions problems with around 80K miles on this mod and my otherwise stock engine, stock replacement radiator and OEM waterpump still...