You can determine which
sensor is setting off the
alarm with a meter. The switch in question will have a short across it's terminals.
What is the temp gauge reading when the
engine is warmed up? Up to 185 is normal. You said you have 100 kpa oil pressure when hot. If this is at idle, it might be OK. At cruising
RPM, that's definitely abnormal.
Don't take the thermostat out. It's the resort of all mechanics who have no understanding of how
cooling systems
work. If the
engine is
overheating you can change it.