Just joined. I wish to exchange the coolant on my Toyota Yaris as it had never been done in the 10 years I have owned the vehicle. I have bought the recommended, premixed coolant and 2 gallons of distilled water to flush the system.
I have looked at quite a few YouTube videos on changing coolant and there is something that I don't understand. First I will state the "problem" as I see it - then if someone can explain exactly what happens I will be grateful.
Is the following correct? When a water-cooled car or bike engine is cool, there are effectively two separate cooling reservoirs. One circulates through the radiator and is pumped by the water pump. The second reservoir surrounds the engine block. These two reservoirs are kept separate by the thermostat. As the engine heats up the water surrounding the engine heats up until it reaches a temperature when the thermostat opens and connects the two reservoirs. The (very) hot water from the engine block is pumped through the radiator to dissipate some of the engine heat.
Now, if I drain the coolant from the radiator through the drain plug at the bottom of the radiator when the engine is cold then am I only draining the radiator because the thermostat is closed? If I refill, surely I am only replacing the drained radiator coolant? The original coolant around the engine block will not have drained? I can't drain the radiator when the engine is hot because super-heated water will escape. If only the radiator has been drained when cold, surely the coolant around the engine block has remained? Then after refilling the radiator, when I run the car and it gets to operating temperature, the old (engine) and new (radiator) coolant will mix? Or if I try to flush with distilled water, at operating temperature the engine coolant will mix. An opposite problem will occur after I have flushed with distilled water, and start introducing coolant, the new coolant will be diluted by the distilled water around the engine block?
Can someone correct my (mis)understanding so I perform this coolant exchange correctly?