your motor doing excactly same as mine, problems were as follows, yes the thermostat was stuck in open position,renewed,a/c not activating,needs to be filled/recharged , radiator flushed, fill system and thorough bleeding ie; remove bleed screw and fill through the bottle and bleeder, temp setting on full and blowers on 1/4 power,start engine and allow thermostat to open,large jug of coolant spare, leave cap off and allow to flow throufgh bleed hole, when you see a good stream inside your bottle ie;(little hole in neck inside exp tank ) replace cap and bleed screw, don,t touch a/c as this will take longer to warm up with the fan running(assuming you have electric fan that is) whilst warming up give the top and bottom hoses a few squeezes, helps with the bleeding, keep an eye on temp guage, if higher than midway, your fan should kick in,check temp again, if too hot switch off, check level, allowing to cool a little first of course and go through bleed again,heater on low and full temp,fill and bleed,fill and bleed until all air is out, hope this helps