Temp sensor

It's worse than that: the sensor bulb in the water pump is right at the point where water cavitates off the pump impeller tips, so you're reading heaven-knows-what as far as "temperature" is concerned, and longevity of the copper bulb won't be great either. The mechanical gauge is a good idea, but I think I'd either drill/tap the head or the block up front for a stable water source, or maybe make some sort of insert for a freeze plug. The waterpump heater line port ain't it.