Preventive maintenance for heavy fleets: intervals, filtration and cost control

In a fleet, every unplanned workshop hour carries two costs: the repair, and the trip that did not happen. The second is usually larger and almost never appears on the work order. That is why fleet maintenance is not judged by what it costs to do, but by what it costs not to have done.

The three service levels

A tiered structure avoids two equally expensive extremes: checking everything every time, or checking only when something breaks.

Engine oil: interval, category and condition

SAE J300 defines the viscosity grade — 15W-40 and 10W-30 are the most common in heavy-duty diesel — and the API categories define the performance level. CK-4 is the heavy-duty category aimed at engine protection with low-sulphur fuels, while FA-4 covers lower HTHS viscosity oils intended for fuel efficiency; the two are not interchangeable in every engine and the manual must be checked.

The interval is not a universal number. It shortens with extended idling, frequent stop-start, dust, high ambient temperatures, constant maximum load and short trips. In quarry or container yard operation a truck can accumulate more engine hours than kilometres, and the interval should then be set by hours.

• Set the interval on whichever comes first: mileage, engine hours or litres of fuel burned.
• Classify each unit by duty severity and apply its own interval, not the fleet average.
• Record oil consumption between services: a sustained rise is an early sign of wear or an intake problem.
• Keep the same product across the fleet wherever technically possible: it reduces the risk of a wrong fill.

Filtration: where engine life is decided

The filter is the cheapest item on the list and the one that most determines the cost of the most expensive component. Oil filter efficiency is tested to ISO 4548-12 and expressed as a beta ratio at a given particle size: it is not enough for the filter to fit, it has to capture the particle size that damages that engine.

• Oil: the full-flow filter protects the engine immediately; a bypass filter, where the engine provides for one, captures finer particles and extends lubricant life.
• Fuel: the water separator is critical. Water in the fuel damages the high-pressure injection system, one of the most expensive repairs on the vehicle. Draining the separator belongs in the daily inspection.
• Air: restriction is judged with the indicator, not by eye. A filter that looks dirty but reads within range is still working; pulling it out to blow it with compressed air damages it and lets particles through.
• Hydraulics: on units with a crane, tipper or boom, the hydraulic circuit needs its own cleanliness target and its own change programme.

Tyres: the second operating cost

After fuel, tyres are usually a fleet's largest variable cost, and their wear responds to variables the workshop controls.

1. 01

   Pressure

   Measure cold with a calibrated gauge. Underinflation raises fuel consumption and heats the sidewall; overinflation shrinks the contact patch and wears the centre.

2. 02

   Alignment and geometry

   Irregular wear on an axle is not fixed by rotating the tyre: it is fixed by finding the cause in toe, camber or worn bushings and springs.

3. 03

   Dual matching

   Two duals of different diameter mean one permanently drags the other. The difference must stay within the manufacturer's stated margin.

4. 04

   Record by position

   Tracking tread depth by position and by unit allows replacement to be anticipated and flags units with an underlying mechanical problem.

Brakes, suspension and steering

The air system needs daily moisture draining and periodic checks of the dryer. On brakes, beyond lining or pad thickness, chamber pushrod stroke and the condition of the automatic slack adjusters must be checked: an adjuster that is not working defeats the system design even with new linings.

In suspension and steering, bushings, springs, shock absorbers and rod ends determine both safety and tyre wear. Rodacaribe distributes PAI Industries and FORTPRO for Cummins, Detroit and Caterpillar engine components and for brakes, suspension, steering and driveline, with multi-brand compatibility.

Batteries and starting system

Most fleet batteries do not die of old age: they die from vibration, loose hold-downs, terminal corrosion and chronic undercharging in units with heavy idling and accessory loads. Periodic load testing and alternator checks cost minutes; towing a stranded truck costs a day.

How to tell the programme is working

• Cost per kilometre or per operating hour, separating planned from corrective maintenance.
• Fleet availability and number of on-road failures per unit.
• Ratio of planned to unplanned work: a mature programme shifts spending towards planned work.
• Schedule compliance: what percentage of services was carried out within the intended window.

These four indicators fit in a spreadsheet. What does not work is judging maintenance by the month's invoiced total: that number falls right before the breakdowns start.