Is the position of the temperature sensor moved with this modification, please? One thing to be aware of is the QED solution isn't without it's own compromises. Warm up is slightly compromised, in that engine temps take a while to stabilise. It's ok if stationary as there is no airflow through the rad, but if driving on a cold day then during warm up there is cold airflow through the rad which further cools the water in the rad so when the stat does open it then dumps a rad and bottom hose full of cold water back into the system, which causes that stat to close again and so the cycle starts again. Will a łarger bypass exacerbate this or make it less likely? Very interesting. The lower the thermal inertia of the water in the bypass (thermostat closed) circuit the less oscillation, other things being equal(!), I think... Jonathan