In answer to your Subject... "No", but I'm learning a lot. How to decrease the thermal downshock from that slug of cold water from the radiator... in the absence of major changes you could either decrease the volume or increase the temperature of the water in the radiator (and that bit of the circuit). A small bypass or hole in the valve would do this by keeping the radiator warmer but would slow the whole system warming up. Why does that lttle coolant circuit to the electrical temperature sender exist rather than the sender being moved? Is it just easier to do the conversion that way? ... once all up to temp then there's no flow difference, however the stat will be reacting to water that has just left the engine not to the temp after it has been cooled via the rad as in the standard setup. At a given heat output from the engine it doesn't matter which side you sense it in control terms although the cut-off value would need to be different.But 4 suddenly made me realise why this problem is harder than I thought. In most control systems the sensor(s) that controls the valve(s) and the valve(s) can easily be separated. In car thermostats they're inherently together. Are there any modern engines or racing engines that separate the sensor(s) and actuator(s)? Are they available off the shelf? That's going to be more expensive and potentially less reliable, but it would make the whole thing much easier to control. Jonathan