Knowing when to change your vehicle’s coolant

Dear Ask a Mechanic,

I have a 2015 Honda Civic that I purchased new which only has around 27,000 kilometres on it. The vehicle’s maintenance reminders don’t indicate when the coolant should be changed, and whether it should be done based on mileage or not. It has been on the road for seven years now. What factors should be used to help decide when the coolant should be changed? – Coolant Curious

Time is a factor in the longevity of certain vehicle fluids. While transmission, differential and transfer case fluids tend not to break down or become contaminated by moisture very quickly, brake fluid and engine coolant both deteriorate with age.

The chemical properties of brake fluid make it hygroscopic, meaning it attracts and holds moisture, even from in the air. As such, Honda recommends that the brake fluid in your Civic be replaced every three years, regardless of mileage. This advice is typical industry wide, though it’s an often-neglected maintenance item.

Engine coolant (or antifreeze) has its own set of properties, not only those for resisting freezing and boil-over, but also for preventing the various metals in the engine, radiator and heater core from corroding. The additives in the coolant that help protect those parts are used up over time, which is the primary reason why it is recommended you change your car’s coolant regularly. The coolant’s actual freeze resistance is not reduced over time.

Because all of Honda’s modern engines use aluminum in both the cylinder heads and block, the antifreeze doesn’t get discoloured to the same extent as in applications where iron components are present, so the fluid may appear okay even when it needs to be changed.

Honda’s reliance on its Maintenance Minder system makes finding a specific time interval for replacing the antifreeze in your Civic a challenge, however we can deduce when to do it by looking at the automaker’s other vehicles.

For example, when I road tested a Honda Ridgeline back in 2017, I spotted a notice included on the emissions sticker under the hood that stated, “The factory installed long-life coolant must be replaced according to maintenance minder sub code 5, or at 10 years, whichever comes first. Thereafter every five years.”

As the Ridgeline uses the same Long-life Type 2 coolant as your vehicle and has a similar all-aluminum engine composition (albeit a V6, rather than a four cylinder), it’s a reasonable assumption that your Civic would have a comparable maintenance interval.

Critically, these lengthy intervals rely on using Honda’s Long-life Type 2 coolant or an equivalent product. Other coolant types will reduce the protection level and could possibly cause damage.

Ask a Mechanic is written by Brian Early, a Red Seal-certified automotive technician. You can send your questions to wheels@thestar.ca. These answers are for informational purposes only. Please consult a certified mechanic before having any work done to your vehicle.