you should also bleed this system!
This is very true.
The bleed screws are not ideal on the older models.
i have had my cooling system done a number of times by Holden and assorted mechanics for various reasons. always hear the coolant sloshing around through the heater.
I have a coolant bottle with the base cut off. Pushed on a slice of radiator hose onto where the lid goes. Now with some support it fits and seals in the radiator opening.
I have a garden glove on hand to wear.
Insert the coolant bottle reservoir and fill up 1/2 way with coolant mix.
Run the car at idle through several thermostat openings, topping up the fluid as it drops. This will still happen even if you bleed the air with bleed screws etc. Shows how little air comes out from them.
Then I get a helper to give the car some good revs and the amount of air that starts to come out again. Small bubbles give way to really big bubbles. levels continue to drop significantly as the air makes way.
i stop once the bubbles stop coming through. Takes about 30 mins or so.
I end up doing this after every time I do anything to the coolant system or someone else does.
This method was shown to me by a Holden technician. They had a special reservoir and I adapted mine from that idea.
It is extraordinary just how much air is trapped in the system after what is considered the normal bleed methods.
I use this method on my newer cars also.