Most small fleets either over-service vehicles (because the dealer says to) or under-service them (because nobody has time to track it). Both are expensive. Over-servicing wastes thousands per year per vehicle in unnecessary parts and labor. Under-servicing leads to the breakdowns that cost 5–20× more than the missed service would have.
This is a working preventive maintenance schedule for a small fleet, broken down by vehicle class. It's not factory spec — those are calibrated for warranty coverage, not real-world economics. It's the cadence that, in practice, keeps a small fleet running without throwing money at unnecessary service.
Light-duty vehicles (vans, pickups, SUVs under 10,001 lbs GVWR)
Examples: Ford Transit, Mercedes Sprinter (light), GMC Sierra 1500, Ford F-150, Ram 1500, service body trucks, utility vans.
| Service | Interval | Notes |
|---|---|---|
| Oil + filter change | Every 5,000 mi or 6 months | Most modern engines spec 7,500–10,000 mi. In stop-and-go fleet use (idling, short trips), service at 5,000 mi for engine longevity. |
| Tire rotation | Every 7,500 mi | Combine with oil service every other time. Catches uneven wear before it forces a premature replacement. |
| Brake inspection | Every 15,000 mi | Pad thickness measurement only. Replace pads at ~3mm remaining. |
| Air filter | Every 30,000 mi | Inspect at every oil change in dusty conditions. |
| Cabin filter | Every 30,000 mi | Driver comfort, not safety. |
| Transmission fluid | Every 60,000 mi (auto) | Skip the dealer's 30K recommendation unless severe duty. Modern ATF is durable. |
| Coolant flush | Every 100,000 mi | Some OEMs spec 150K. Inspect for color/contamination at 60K. |
| Spark plugs | 100,000 mi | Iridium plugs in most modern engines. Don't change early; gap drift before then is minimal. |
| Differential fluid | Every 60,000 mi | Service vehicles only. Skip on light-duty unless towing. |
Medium-duty trucks (Class 3–5, 10,001–19,500 lbs GVWR)
Examples: Ford F-450/550, Chevy Silverado 4500/5500, International CV, dump trucks, large box trucks, larger work trucks.
| Service | Interval | Notes |
|---|---|---|
| Oil + filter (diesel) | Every 7,500–10,000 mi or 6 months | Diesel engines tolerate longer intervals than gas. Use OEM filter — generic filters fail under diesel oil pressure. |
| Fuel filter (diesel) | Every 15,000 mi | Critical for HPCR injection systems. Failed filter = $5K+ injector damage. |
| DEF system check | Every 15,000 mi | Top off DEF, check for crystallization on lines. |
| Tire rotation | Every 10,000 mi | Drive tires wear faster than steers; rotation extends life ~20%. |
| Brake inspection | Every 15,000 mi | Air or hydraulic; measure pad/lining thickness. |
| DOT annual inspection | Annually (required) | Federal requirement for CMVs. Schedule on a fixed date so it never lapses. |
| Air dryer service | Every 30,000 mi (air brakes) | Cartridge replacement. Failure causes moisture in air system → brake freeze in winter. |
| Transmission fluid | Every 100,000 mi | Allison/Aisin/ZF — follow OEM. |
| Front-end inspection | Every 25,000 mi | Tie rods, ball joints, kingpins. Heavy loads accelerate wear. |
Heavy-duty trucks (Class 6–8, 19,501+ lbs GVWR)
Examples: Freightliner Cascadia, Peterbilt 579, Kenworth T680, International LT, Mack Anthem. These are typically interstate or vocational vehicles requiring CDL drivers and ELD compliance.
| Service | Interval | Notes |
|---|---|---|
| Oil + filter | Every 25,000 mi (synthetic) | Modern OEM-spec'd synthetics support 40K+ miles in line-haul. Vocational duty: 15–25K. |
| DOT inspection | Annual | FMCSA-required. Out-of-service violations are expensive — schedule and track religiously. |
| Air brake adjustment | Every 50,000 mi or quarterly | Self-adjusting slacks still drift. Out-of-adjustment = OOS violation. |
| Tire condition + pressure | Weekly (driver) + monthly (formal) | Single tire blowout can total a $2K casing. Pressure check is the cheapest insurance you have. |
| Coolant filter | Every 25,000 mi | SCAs degrade. Cavitation pitting destroys cylinder liners. |
| PMI (Preventive Maintenance Inspection) | Quarterly | Comprehensive: brakes, steering, suspension, electrical, fluids, exhaust, lights, body. Track to the chassis. |
Time-based services (regardless of mileage)
Low-mileage fleets (real estate, property management, supervisor vehicles) often miss services because miles accumulate slowly. These are time-based:
- Oil change: every 12 months max, even if under interval. Old oil oxidizes.
- Battery test: every 12 months. Most fleet batteries fail at 3 years, regardless of mileage.
- Tire age: replace at 6–7 years from DOT date code, even with tread remaining. Sidewall failures kill underused tires.
- Coolant: 5 years max, regardless of mileage. Inhibitor depletion is time-based.
- Brake fluid: 2–3 years. Hygroscopic — absorbs moisture, lowers boiling point.
Driver-side daily checks (the 60-second pre-trip)
Every driver, every shift. This catches 80% of avoidable failures before they happen:
- Walk around the vehicle: damage, flat-looking tires, fluid puddles under the truck.
- Lights: headlights, taillights, brake lights, turn signals. Quick visual.
- Mirrors: positioned and clean.
- Engine bay (weekly, not daily): coolant level, oil level, washer fluid.
- Dashboard at start: warning lights cleared, fuel level adequate, mileage logged.
This isn't a DOT pre-trip — that's separate and required for CMVs. This is the practical fleet version that any driver of any vehicle should do.
How to actually track this
A schedule on a Google Doc that nobody opens is worthless. The minimum tracking setup:
- Each vehicle has a record with last service date and mileage for each interval above.
- An alert fires when a service is due in the next 500 miles or 14 days.
- Driver pre-trip checks are logged digitally (or at minimum dated) so you can audit them later if something fails.
- Repair records are linked to the vehicle, not stored separately by date.
This is the core of any fleet management system — including Fleiko. If you're tracking it in spreadsheets today, the upgrade is reminders that fire on time, not a fancier sheet.