I thought I would give my veiwers the run down on Thermostats, what they do, how they work and the importance of cooling system service. I often get vehicles with faulty Thermostats. Please see below pic of the cooling system to give you a broader view of what i'm trying to explain.
A Thermostat slows and speeds coolant flow in the form of a resistance valve (thermostat) to allow coolant to cool at a slower rate, keeping the vehicle at it's specified normal running temperature. Gone are the days when you can cut the center out of a thermostat to get you going. Overtemp especially with vehicles with alloy and plastic radiators are fragile and overtemp means overpressure, it can also blow gaskets and seals all over the cooling system.
To avoid your cooling system being damaged you can get it serviced and the thermostat replaced every 2 years, avoid putting water in your cooling system and only use a full concentrate 5ltr bottle, no water. Water is a corrosive it carves valleys in mountains and does the same to your cooling system, some of the chemicals in water such as chlorine and flouride have an effect on the chemicals in the coolant such as glycol, if you must top up with water, use a demineralized water. Use a top quality coolant such as Penrite. And pay the extra for a genuine Thermostat as most aftermarket thermostats open at a different temp.
Damage: A closed Thermostat can, and often causes headgasket failure, cylinder bore glaze and cracked cylinder heads, not to mention expanded cooling systems. If you have a faulty thermostat it won't always let you know by the temperature guage, depends on the design of the engine if they place the sensor before or after the thermostat, I wonder sometimes if these Mechanical Engineers actually use the brain required to become an engineer, some of the cooling systems on thes new cars are simply not made for Australian climate and road conditions, imports are imported with the full flow thermostats for colder climates, they run fast flow coolant and overtime (at the end of the warranty period) the cooling system starts to leak and breakdown due to years of overpressure, all because they are not bothered to install a slower flow thermostat for Australian conditions. Imports which are now all new cars are generically made and exported to the world, no cars are made for our conditions except Toyota. Holdens are no longer Australian, they are Euro, hang your head in shame Holden, you're filling the road with shitboxes.
So that's a pretty good run down of a Thermostat, don't let the backyarder cut the guts out of your thermostat and she'll be right mate, do the right thing and get your cooling system serviced by a qualified mechanic, a drain and re-fill is NOT a service!