The sticker on the expansion tank says one thing, the owner's manual says another, and your workshop sees failures at a third interval. Setting a fleet schedule that actually works means understanding why the numbers differ.
Why published intervals vary so much
| Factor | Effect on real service life |
|---|---|
| Inhibitor technology | IAT depletes in about two years; OAT and hybrid packages run three to five years or more |
| Coolant concentration | Over-dilution shortens life severely; a 50 % mix holds much longer than a 20 % mix |
| Water quality | Hard water adds scale and chlorides, which consume inhibitors and attack aluminium |
| Duty cycle | Continuous high load and heat cycling accelerates inhibitor depletion |
| System condition | Existing corrosion product keeps consuming fresh inhibitor after a change |
| Metal mix | Iron, aluminium, copper and solder together place more demand on the package than a single-metal system |
| Ambient climate | Sustained high temperature raises acidification and evaporation losses |
Setting intervals by duty cycle
| Duty category | Example vehicles | Suggested coolant interval |
|---|---|---|
| Light duty, temperate | Passenger cars, small vans | Follow OEM; typically 5 years |
| Light duty, tropical | Ride-hailing fleets, delivery vans | 3 – 4 years; test at year 2 |
| Medium duty | Light trucks, minibuses | 2 – 3 years with annual testing |
| Heavy duty, long haul | Articulated trucks, coaches | 1 – 2 years with testing at each service |
| Severe duty | Mining, construction, generator sets | Annual change plus mid-year testing |
The four checks worth doing regularly
- 1Level and appearance, at every service. Falling level means a leak; discolouration means contamination or a depleted package. Both are early warnings that cost nothing to spot.
- 2Freeze point by refractometer, every six months. A reading that has drifted upward since the last service means someone is topping up with water.
- 3pH with test strips or a meter, annually. A pH that has dropped toward neutral or below is the clearest sign the inhibitor reserve is exhausted, even when the coolant still looks clean.
- 4Pressure cap and thermostat, on the interval the maker specifies. These two components cause a large share of overheating complaints and cost very little to replace.
Building it into the service record
Record the coolant product, concentration and test readings against each vehicle. A fleet that knows what is in every cooling system avoids the most expensive coolant failure of all: a service technician topping up an unknown OAT system with an IAT product because nobody wrote it down.
Browse the coolant range
Grades from 0 °C tropical coolant through to − 45 °C severe-winter antifreeze.
Related topics
coolant change intervalfleet coolant maintenancecoolant service lifecoolant testing intervalheavy truck coolant maintenance