I proudly boasted to Toshi 975 that, having fitted a replacement thermostat, for the first time ever I seemed to have one which acted with a bit more than just an ON/OFF response and worked properly in response to ambient temperature and heating requirements.

Having pushed the engine quite hard recently, despite the cold weather, I was getting a bit suspicious that something wasn't quite right because I had never seen the cooling air exit flap fully open.

I decided to use a full assembly from an old engine, to include the rod which connects it to the exit flap. But the rod off that 650 engine was slightly cranked and seemed to be designed to fit only one way round. This is different to most of the rods I have seen before, which are straight and can be fitted either way round. I double-checked another 650 engine and this also has a slightly bent rod.

What seemed to have been happening previously was either that the straight rod was catching on something or (more likely), the thermostat was being put under some unintended strain.

I don't know if this design change matches some internal difference in geometry within the thermostat cowling of the bigger engine; it certainly has some obvious external differences. But I haven't seen a different rod available from any supplier despite it having the potential to mess up the cooling efficiency.

Has anyone else seen this?