How to change antifreeze
Changing coolant is not difficult work, but there are two stages where people most often go wrong: flushing the system and bleeding the air. Skipping either means good new fluid cannot do its job.
The steps
- The engine must be completely cold. Opening the cap on a hot system risks serious burns, because the fluid is under pressure and erupts.
- Drain the old fluid from the radiator's bottom plug. Many cars also have a separate block drain, and if yours does, open it too, otherwise a third of the old fluid stays in the system.
- Flush. Fill with clean water, run the engine to operating temperature with the heater on, shut down, cool and drain. Repeat until what comes out runs clear.
- Mix in a separate container at 50/50 or 60/40.
- Fill slowly and top right up.
- Bleed the air. Many cars have a bleed screw on the radiator or thermostat housing. Run the engine with the cap off and the heater on maximum until the fan cycles, adding fluid as the level drops.
- Check the level a week later on a cold engine. It almost always needs a little more.
The air pocket, an invisible enemy
An air pocket left in the system causes two problems. The first is that air carries no heat, so the metal at that spot overheats locally. The second is that a pocket can sit at the thermostat or the temperature sensor and give you a false reading: the gauge looks normal while the engine boils.
Bleeding a hybrid inverter circuit is a separate procedure and often requires a diagnostic tool. That is exactly why Honda assigns this job to a dealer.
The three most common mistakes
First: “I only drained the radiator.” This leaves much of the old fluid in the system, and the new fluid is contaminated immediately.
Second: “I topped up with water.” One litre of water in a seven-litre system takes a 50/50 mix down to roughly 43 per cent, costing you several degrees of freeze protection.
Third: “I mixed two different colours.” The inhibitor packages neutralise each other and sludge forms. Honda prohibits this outright.