would suspect with that code its thermo housing , would also check no coolant leaks as this can add air to around the temp sensor area and also flag a mismatch code for temps , would always replace the plastic link pipe from thermo housing to water pump as these crack all the time 6-8 years life span common before heat and plastic breaks down, would also change coolant while its apart, if water pump over 70k would also include that for piece of mind and its coated pulley and aux belt,
yes my suspicions were cemented with your response. Here is the thing. I did add coolant initially and the light did go off for a period of time, if I recall correctly, but the problem was that I poured coolant a little bit on the high end. If there is a leak, its not leaking at parked intervals, it must be blowing out while driving. But I'm not seeing splash spots under the hood on the engine from blow by coolant. I do not see any cracks in the hoses, but by the same token, I shouldn't have to add coolant 2-3 times, should I? I've ordered a new thermostat based on vin# and should arrive in a few days.
Honestly, I do like this car as it does have many little perks but by the same token it certainly does seem like there are many little PIA nuances with it
these engines should keep coolant level same all the time should use zero coolant, common issues i have found with them is the header tank cap if it dont hold the pressure the coolant will travel in to header tank and push the air pocket in header tank in to the top of the head and the thermostat housing ie then coolant sensor is in air and not coolant and will flag such a code,, as when first start until reaches higher temps the coolant stays around sensor,, but as pressure climbs the cap leaks and air then suddenly hits sensor ,, ie thats why it happens after a while driving,
another thing that happens is the plastic kink pipe breaks inside the back of water pump the rubber seal then moves slightly and only leaks with pressure and movement vibrations from the engine so only leaks when driving up the road,,, best way to tell is drive car until fan in and out and then leave a piece of card under the car for a few hours,, when come back where ever you have a wet spot is where leak is,, if under the water pump most likely that link pipe,, but would do all 3 things at same time if replace them, thermo housing , water [ump. and link pipe,, i would also fit new header tan cap as only around £15 ish to replace,