500 Two-Stroke Tech

I rode my bike for the first time tonight, after having run the engine up to temp on several occasions in the past few weeks.

I let it get up to 70deg C before I rode it but the coolant temp drops straight away to about 50 when I ride it. I have an R6 2CO radiator which is way bigger than standard and its close to 2degC here at the moment so maybe I'll have to mask of some of the radiator?

Why does the temp drop so quick? The temp sensor is on the "engine" side of the thermostat, right?? Shouldn't the thermostat keep the engine water temp up at about 70 deg, only opening up if the engine gets too hot?? I know that some water passes through even when the thermostat is "closed" but i thought the engine temp would stay up.

Never mind. 55 +/- 5 is what you want anyway.
Seemly the thermostat is either removed or faulty ( stuck open).
I run as low as 38 deg C with my RD350 in winter. No need to mask anything off.

Great. Thanks for this Martin. That's lower than I expected. I checked the thermostat in hot water and it's working as specified.

If it works, then maybe someone swapped it with a 50deg one?