For most drivers, a new vehicle is their second biggest financial investment after their home, and they need it to run reliably for many years. Cooling system maintenance is one of the most important, yet most often neglected service items.

Gasoline engines can produce tens of thousands of combustion events per minute with flame temperatures exceeding 1,000 degrees Celsius. The cooling system has to efficiently absorb and dispose of that heat energy to prevent engine damage.

The engine’s coolant flow passages are carefully engineered to help ensure temperatures remain stable and even, with no hot or cold spots. Whether in extreme cold or blistering heat, coolant must flow through those passages without freezing or boiling to work properly. Specially formulated engine coolant – typically based on a blend of ethylene or propylene glycol and de-mineralized water – can function over a temperature range of −36°C to +129°C. Other additives in the coolant help to inhibit corrosion of metal parts and lubricate the water pump.

Over time, coolant degrades due to the limited lifespan of its corrosion inhibitors and lubricants. Without the corrosion inhibitors, scale can build up and restrict flow in the cooling passages, heater core and radiator tubes. Advanced corrosion can cause leaks to develop, resulting in overheating and engine damage requiring very expensive repairs. A damaged engine can easily cost thousands of dollars to repair, while cooling system maintenance is relatively inexpensive by comparison.

The traditional glycol-based coolants used in Honda vehicles up to 1997 required replacement every two years or 48,000 kilometres. From 1998 onward, Honda vehicles use long life coolant that is initially formulated to last ten years or 192,000 kilometres, then requiring replacement at intervals of five years or 96,000 km thereafter. More recent models with Maintenance Minder systems use the same long life coolant; however, replacement is not scheduled by time or distance and is required only when Maintenance Minder Sub Item 5 is displayed.

Although today’s coolants lasts longer, the cooling system must still be checked and maintained regularly, according to the schedule in your Honda’s owner’s manual or maintenance guide, or according to its Maintenance Minder system.

You can do your part by observing the temperature gauge (if equipped) for any indication of the engine running abnormally hot or cold, monitoring the coolant level in the reservoir and watching for signs of leakage when doing your under-hood checks with fuel fill-ups. Coolant on the ground where you park your vehicle is a sure sign that attention is required.

The first step of cooling system maintenance is a pressure test. In order to raise the boiling point of the coolant above 120°C, all modern vehicles use pressurized systems. With the engine off and cold, a test device can pressurize the cooling system to check for leaks. The pressure ratings vary for different vehicles, but if the pressure holds steady at the specified level, the system should be free of leaks. The pressure cap should also be tested to ensure that it holds and releases at its rated pressure. If it releases at too low a pressure, the coolant can boil, while excessive pressure can cause hoses or gaskets to burst. Your dealer’s service department has the tools and the expertise to complete these tests quickly and accurately.

The rubber hoses that transfer coolant between the engine, radiator and heater core should be inspected for cracks or bulges. The belt that drives the water pump (external pump not driven by the timing belt) should be checked for cracks or stretching. A problematic hose or belt should be replaced immediately.

The cooling fans on Hondas are driven by electric motors and are controlled by thermostatic sensors and relays. The condition of the fan blades should be inspected and the fans should be observed while the engine is running to make sure they cycle on and off. If the engine is running hotter or colder than usual, the cooling fan controls should be tested to make sure they are switching on and off at the proper temperatures.

Both sides of the radiator (and A/C condenser, if equipped) should be carefully inspected for damage and accumulation of debris. Dead bugs and other road dirt that inevitably build up during driving should be carefully rinsed off. Bent fins should be straightened with a comb tool to restore air flow.

A thermostat in the system controls the flow of coolant between the engine and radiator to maintain proper engine operating temperature and speed up cold start engine warm-up. A sticking thermostat can also cause the engine to run abnormally hot or cold and can be tested and replaced if it doesn’t open or close at the correct temperature.

The freezing and boiling points of the coolant can be checked by using a special tool to test its specific gravity. If its freezing point is too high or its boiling point is too low, its concentration should be increased or the coolant should be replaced.

The coolant is usually drained through a valve on the radiator. Some vehicles also have a drain bolt on the engine block. After draining, the system should be thoroughly flushed with water until it runs clear and free of the colour of the coolant. Powered flushing done in the reverse of the usual flow direction helps to loosen and remove any scale or other contaminants that may have accumulated.

Coolant that is not being re-used should always be collected for recycling or proper disposal (refer to local environmental regulations) and never dumped in a sewer or waterway. Honda dealers have equipment to collect used coolant and send it to a recycling facility for reprocessing.

The sweet smell of glycol is attractive to many animals, but it is toxic and potentially fatal if ingested, so coolant should never be stored in an open container accessible to pets or wildlife.

After closing up the drain(s), the system should be refilled with a 50/50 mixture of coolant and water. With the radiator pressure cap still off, the engine should be run with the fresh coolant for about 10 to 15 minutes to bleed any air out of the system. Air in the cooling passages will limit the pressure, which will lower the boiling point and potentially cause damaging hotspots in the engine. During this bleed procedure, the interior heating system should also be turned on high to ensure that air is forced out of the heater hoses and core. Once it has been bled, the system should be topped off with coolant mixture, typically through the reserve tank, and the pressure cap should be reinstalled.

If you do not have the necessary experience or equipment to perform your own cooling system maintenance or repairs, leave it to be done by your Honda Dealer – their Service Department has the knowledge, tools, parts, and experience necessary to properly maintain your vehicle’s cooling system.