When to change your coolant
Coolant does not wear out the way oil does. Its glycol stays essentially unchanged. What depletes is the inhibitor package, the chemical additives that protect the metals. When they are gone, the fluid looks the same and the protection is simply no longer there.
The official interval
According to the data sheet, Zerex Asian Blue's service life is 5 years or 240,000 km, whichever comes first.
That interval assumes the fluid went into a clean system, was mixed correctly and has not been contaminated with another chemistry. In Georgian conditions, meaning mountains, heat and traffic, it is sensible not to run it to the very end.
If the car is used and you do not know its history, start the count from zero: flush, refill and write down the date.
How to check it yourself
With the engine cold, open the expansion tank and look at the fluid:
- Bright and clear. A good sign.
- Dull and cloudy. The inhibitors are depleting.
- Brown or rust-coloured. There is corrosion in the system, so change it immediately.
- Sediment at the bottom. Either silicate dropout or scale, and it needs flushing.
- An oily film or a milky tint. Oil may be entering the system, which is a diagnostic matter rather than a fluid one.
For a more precise check, a refractometer or hydrometer measures the mix percentage and freeze point.
When not to wait for the interval
- If the engine has overheated even once.
- If the system was repaired and drained.
- If somebody topped it up with a different colour.
- If water was added and the system has not been flushed since.
- If you have just bought the car and do not know its history.
In all five cases the interval starts again from zero.