Most service schedules are written in miles: an oil change every so many thousand miles, filters every so many more. That works for a truck that spends the day on the highway. A school bus is different. It stops every few hundred yards, idles at schools while students load, warms up for 10 or 15 minutes on cold mornings, and may sit running at a field trip. The engine is working the whole time, but the odometer barely moves.
That's why the engine hours vs miles question matters for school buses. Here's how to tell which clock fits each bus, and how to use both.
The hours-to-miles ratio
Divide a bus's miles by its engine hours over the same period. The answer is its average speed while the engine was running, and it tells you how the bus is really used:
| Average speed | What it usually means | Which clock to watch |
|---|---|---|
| Over 30 mph | Highway or long rural runs, little idling | Miles are fine |
| About 15 to 30 mph | A typical mix of town and country routes | Both: whichever comes first |
| Under 15 mph | Tight town routes, lots of stops and idling | Engine hours |
For example, a bus that drives 70 miles a day with the engine running 5 hours averages 14 mph. On a 5,000-mile oil interval it would go about 357 engine hours between changes, which may be more than the engine maker allows by hours. On that bus, the hours run out first.
Tip: Check the ratio once a year for each bus, from the odometer and hour meter at the start and end of the school year. Buses move between routes, and a bus that was on a highway run last year may be on a town route now.
Why idling counts
- The engine wears and the oil breaks down whether the wheels turn or not.
- Long idling on diesels can build up soot and fuel in the oil, which is why some makers shorten intervals for heavy idling.
- Cold-weather warm-ups and school pick-up lines add hours with almost no miles.
- Many states and towns limit idling for school buses anyway, so cutting it saves fuel and service too.
Setting the intervals
- Start from the engine maker's manual. Many give intervals in both miles and hours, and a severe-service schedule for stop-and-go use.
- Use both, whichever comes first, so a bus that idles a lot is caught by hours and a bus that runs far is caught by miles.
- Add a time limit too, such as once a year, for a bus that doesn't run much.
- Read the hour meter at every service and fuel-up where you can, not just the odometer.
- Adjust with oil analysis if you use it: it shows whether your interval is too short or too long.
Good to know: Engine makers, warranty terms and state inspection rules differ. Follow the manual for your engine and keep the records your warranty asks for.
Doing it in FleetCommander
Both clocks on each bus. Each bus's record has Odometer (mi) and Engine hours. Inspections and fuel fills move the odometer up, and each work order has its own Odometer (mi) and Engine hours: when it's completed, the bus's readings move up to match. Update Engine hours on the bus's record when you read the hour meter.
Whichever comes first. On Maintenance, New schedule asks for the Vehicle and Task name. Under Due when… (any that apply), fill in Every (miles), Every (engine hours) and Every (days), and the first one reached makes it due. It shows Due soon, Due and Overdue, and Create work order turns it into a job. When that work order is completed, the schedule starts counting again from its readings. See the Maintenance guide.
Ava (Beta), the assistant in the app, answers Bus 104 engine hours or Any oil changes overdue?. More on her page.
Related reading
Questions people ask
- Is it better to track engine hours or miles on a school bus?
- Track both and service at whichever comes first. Buses on slow, stop-and-go routes with a lot of idling usually reach their hours limit before their miles limit.
- How do you convert engine hours to miles?
- There's no fixed conversion. Divide a bus's miles by its engine hours over the same period to get its average speed, and use that to compare the two.
- Does idling count toward maintenance?
- Yes. The engine wears and the oil breaks down while idling, and some engine makers shorten intervals for heavy idling.
- Where do you find a bus's engine hours?
- On the hour meter on the dash, or from the engine's computer. Write it down at every service so the next one can be worked out.