Idle Fuel Burn, Cost, and Engine-Hour Equivalent

A heavy-duty diesel at idle burns something near 0.8 gallons an hour, more with the HVAC loaded and more again on an older engine. That is a small number per hour and a very large one per year, and because idling produces no miles it is entirely absent from a cost per mile model built from fuel divided by odometer -- it silently inflates the per-mile fuel number instead of appearing as its own line. The engine-hour line is the second cost and the one fleets underestimate. Maintenance intervals are driven by engine hours as much as by miles, and an idling hour is conventionally counted as somewhere around seven road miles of wear, so a truck idling six hours a day accrues the maintenance equivalent of a substantial extra route every year and reaches its overhaul far earlier than the odometer suggests. A truck idling 6 hours a day over 250 operating days at 0.8 gal/hr burns 1,200 gallons, which at $4.10 is $4,920 a year per truck and $98,400 across a twenty-truck fleet, plus the wear equivalent of 10,500 extra miles on each one. Against 2,200,000 fleet miles the idle fuel alone adds about 4.5 cents to every mile the fleet runs, which is roughly what an auxiliary power unit or a bunk heater costs to amortize -- and that comparison is the whole point. An operating estimate; the trucks' own telematics idle data and fuel records govern.

annual_idle_hours = idle_hours_per_day x operating_days; annual_gallons = annual_idle_hours x idle_gph; annual_cost = annual_gallons x fuel_price; fleet_cost = annual_cost x trucks; equivalent_miles = annual_idle_hours x miles_per_engine_hour; cents per mile = fleet_cost / fleet_annual_miles x 100.

Idle fuel burn at the engine's idle consumption rate (near 0.8 gal/hr for a heavy-duty diesel, entered rather than bundled) and the conventional engine-hour-to-road-mile wear equivalence used in fleet maintenance planning, by name. The trucks' own telematics idle data and fuel records govern.

Multiplication on the fleet's own operating figures; the idle rate and the wear equivalence are entered rather than bundled.

Estimate. AHJ and licensed professional govern.

Field names used by the API: idle_hours_per_day, operating_days, idle_gph, fuel_price, trucks, miles_per_engine_hour, fleet_annual_miles, annual_idle_hours, annual_gallons, annual_cost, fleet_cost, equivalent_miles, cost_per_mile_cents

• Idle rate near 0.8 gal/hr for a heavy-duty diesel; higher with HVAC load or an older engine; entered, not bundledfleet fuel practice
• Wear equivalence an idle hour conventionally counted as roughly 7 road miles of engine wearfleet maintenance planning
• Invisible per-mile idling produces no miles, so it never appears in a fuel-divided-by-odometer cost modelfleet cost accounting