Here's the problem...I have an 01 WR426 (it has a 444 big bore kit a Boyesen Water Pump housing and impeller, and some other mods that aren't really relevant to the problem I'm having). When I ride, coolant expands and flows out of the radiators like it should, and accumulates in the catch tank. So far so good. As the bike cools, it should siphon the coolant back into the rads. The operative word there is "should". It doesn't. After a ride, the catch tank is full, and the radiators are down several ounces of coolant. I drain from the catch tank and refill the rads, only to repeat the next ride. I am running "Coolanol" with water wetter mixed per the instructions. At first, I thought the overflow line might be pinched or kinked. I took a look, and no, it's not. I had put a slip fit barbed union in each line to allow me to disconnect the lines and remove the subframe without draining the coolant. I thought one of those might be leaking vacuum on cool down, so I replaced the hoses and did not splice them. Still no joy. Only other thing I can think of is to replace the radiator cap. Am I missing something? Any help or experience is appreciated.