Preventive Maintenance Interval Planner
The manufacturer's interval was set for a vehicle that is not yours, on roads it will never see. This planner shortens it by the severity you specify, converts the result into days between services and services per week, then checks the answer against how many bays you actually have.
Your numbers
The manufacturer's normal-duty figure from the handbook, before you adjust anything.
How far you shorten the interval for your conditions: dust, gradient, stop-start, sustained overload, extreme heat. Enter 0 to follow the handbook exactly.
Use the twelve-month average. A planner built on your busiest month sizes a workshop you cannot fill.
One duty type and one interval at a time.
Preventive services your bays can complete in a normal week, after the breakdowns that jump the queue.
Result
Planned service interval
17,000 km
OEM interval shortened by 15% for your duty severity.
- Days between services
- 69 days
- Services per vehicle per year
- 5.29 services
- Fleet services per week
- 4.1 services
- Workshop capacity used
- 34 %
- Extra services per vehicle per year vs OEM
- 0.79 services
The formula
- Severity reduction is clamped to the range 0 to 90 percent
- Planned interval = OEM interval × (1 − (Severity reduction ÷ 100)), floored at 1 km
- Distance per year = Distance per month × 12
- Services per vehicle per year = Distance per year ÷ Planned interval
- Days between services = 365 ÷ Services per vehicle per year
- Fleet services per week = (Services per vehicle per year × Vehicles) ÷ 52
- Workshop capacity used = (Fleet services per week ÷ Workshop capacity) × 100
- Extra services per vehicle per year versus OEM = Services per vehicle per year − (Distance per year ÷ OEM interval), floored at 0
Assumptions and limits
- Severity is your number, not ours. We will not supply a multiplier for dust or gradient, because a credible one would have to come from failure data for your engines on your routes, and inventing it would make this planner worse than the handbook.
- Distance-based intervals only. Time-based and engine-hour schedules are not modelled, and for a vehicle with a PTO or heavy idling, hours are usually the honest trigger rather than kilometres.
- Every service is treated as identical and interchangeable. Real schedules alternate minor and major, and a major occupies a bay for considerably longer than the capacity figure assumes.
- Breakdowns are excluded, so capacity used is optimistic. Unplanned work does not queue politely behind the plan.
- Distance is assumed even across the year. Seasonal fleets will service in clusters no matter what the average says.
- Shortening intervals is not free and this planner does not price it. More services means more parts, more fluid and more hours off the road, and past a point the reliability gain stops paying for them.
Why the handbook interval is a starting point
Manufacturer intervals are set under defined normal-duty conditions: sealed roads, moderate temperature, rated load, steady running. Almost no working fleet operates there. A tipper on a haul road ingests dust that shortens oil life. An urban distribution van spends its day at engine temperatures that never settle. A truck loaded to its limit on gradient works harder for every kilometre it records.
The odometer cannot see any of that. It counts distance, and distance is a proxy for wear that happens to be convenient rather than accurate. Severity adjustment is how you put back what the proxy discards.
Set severity from your own failure history
The right way to pick the reduction percentage is unglamorous. Open the last two years of work orders and look at what failed between services. Used-oil analysis, if you run it, is better still: a sample that comes back degraded well before the interval is telling you the number directly.
The wrong way is to copy a figure from an article. Two fleets running identical vehicles can sit at opposite ends of the range because one works a quarry and the other runs motorway trunking. If you genuinely have no history, start conservative, sample the oil, and let the results move the number rather than the other way round.
The interval you choose is a workshop plan
Shortening the interval by a quarter increases your annual service count by a third, and that lands on the same bays and the same fitters. This is the step fleets skip: the maintenance policy is decided in one meeting and the capacity consequence arrives months later as a backlog.
Watch the capacity figure here as closely as the interval itself. Once planned work fills most of the week, breakdowns have nowhere to go, and preventive services start slipping to make room. A schedule that is regularly missed by three weeks is not a shorter interval than the handbook. It is a longer one, arrived at accidentally.
Frequently asked questions
Start from the manufacturer's normal-duty figure, then shorten it by an amount you can defend from your own evidence: work orders showing what failed between services, and used-oil analysis showing whether the oil was finished before the interval was. Set the number, run it for a year, then adjust. An interval that never changes has never been tested.
Because we would be inventing it. A number like that only means something if it comes from failure data for your engines, your loads and your roads, and we have none of those. Anyone quoting you a confident multiplier for dusty conditions is quoting a figure with exactly the provenance this paragraph would have had.
No. Every service is an opportunity for an induced failure: a fitting left loose, a seal disturbed, the wrong filter. Over-servicing also consumes bay hours that breakdowns then cannot have, which pushes real defects further back in the queue. The safest interval is the one your evidence supports, in either direction.
On whichever better tracks wear for that duty. Long-haul trucks wear roughly in proportion to distance. A vehicle with a PTO, a refrigeration unit, or an urban round with heavy idling accumulates engine wear the odometer never records, and hours are the truer trigger. This planner is distance-based, so for those vehicles it will under-service unless your severity reduction absorbs the difference.
Whether the interval you just chose is a plan or a wish. It compares the preventive services your schedule generates each week against the ones your bays can finish, before any breakdown arrives. If it reads near or above 100, the schedule will slip, and it will slip on the vehicles nobody is complaining about yet.
Stop estimating. Measure it.
Preventive Maintenance Interval Planner gives you the arithmetic. Fleet Maintenance Software gives you the live numbers from your own fleet.