Engine coolant (antifreeze) protects your engine from both overheating and freezing, prevents internal corrosion, and lubricates the water pump seal. Over time, the additives in coolant break down, its pH changes, and it loses its protective properties. A coolant flush replaces all the old fluid with fresh coolant, restoring full protection. This guide covers the complete procedure.
When to Flush Your Coolant
Most manufacturers recommend a coolant flush every 2 to 5 years or 40,000 to 100,000 km, depending on the coolant type. Conventional green ethylene glycol coolant has a shorter life (typically 2 years or 40,000 km), while long-life coolants (typically pink, red, or blue) last 5 years or 100,000 km or more. Your workshop manual specifies the interval and the exact coolant type for your vehicle.
Choosing the Right Coolant
Never mix different coolant types. Green (IAT), pink/red (OAT), and blue/purple (HOAT) coolants use different corrosion inhibitor chemistries, and mixing them can cause the additives to react, form gel-like deposits, and clog passages. Your workshop manual specifies the exact coolant type and the correct water-to-concentrate ratio (typically 50/50). Always use demineralised or distilled water when mixing coolant, not tap water, as minerals in tap water can cause scale buildup.
Flush Procedure
Work on a cold engine to avoid burns from hot pressurised coolant. Place a drain pan under the radiator and open the radiator drain tap (petcock) at the bottom of the radiator. If there is no petcock, remove the lower radiator hose. Some engines also have drain plugs on the engine block that allow more complete draining – your workshop manual identifies their location.
Once drained, close the drain tap, fill the system with clean water, run the engine to operating temperature with the heater on maximum (this circulates water through the heater core as well), then drain again. Repeat until the water runs clear. This typically takes 2 to 3 flushes.
After the final flush, close all drains and fill with the correct pre-mixed coolant or a 50/50 mix of concentrate and distilled water to the system capacity listed in your manual. Many cooling systems have bleed points (small screws on the thermostat housing or radiator hoses) that need to be opened during filling to release trapped air. Air pockets in the cooling system can cause hot spots and localised overheating. Your workshop manual identifies the bleed point locations and the filling procedure.
After filling, run the engine to operating temperature with the heater on, check for leaks, and top up the expansion tank once the system has cooled.
Your Manual Has the Specifics
Coolant type, system capacity, drain and bleed point locations, and thermostat specifications are all vehicle-specific. Your workshop manual has these for your exact model. MechanicMate offers PDF workshop manuals for over 960 vehicles at mechanicmate.net/shop.
