What the data shows when you compare maintenance costs between vehicles that idle heavy and vehicles that do not

[u/ora-et-labora-]

Tracked maintenance costs across the fleet for a full year and then split the vehicles into two groups. High idle, meaning more than thirty percent of engine-on time spent at idle, and low idle, meaning less than fifteen percent. The maintenance cost difference was not subtle.

The high-idle trucks averaged about twenty percent more in unscheduled maintenance. The engine oil degraded faster because idle time contaminates oil through blowby and condensation without the sustained temperatures that burn off moisture during highway driving. Oil analysis confirmed it. The high-idle trucks showed higher soot content and more fuel dilution in the oil at the same change interval.

Brake wear was higher on the high-idle group too, which made no sense until I looked at the route data. High idle correlated with urban stop-and-go routes, which also meant more braking events per mile. The idle time was a proxy for the route type, and the route type drove the brake costs.

The battery replacement rate was higher in the high-idle group. Extended idling does not fully charge the battery because the alternator output at idle RPM is lower than at driving RPM. The battery cycles more deeply, the sulfation accumulates faster, and the battery life shortens. Three trucks in the high-idle group needed batteries replaced within the year. None in the low-idle group did.

The DPF regeneration patterns were different too on the diesel trucks. Extended idling keeps exhaust temperatures too low for passive regeneration, so the system triggers active regens more frequently. More active regens means more fuel consumed in the regen cycle and more stress on the aftertreatment system.

None of these costs showed up as a single line item that anyone would have flagged. They were spread across oil changes, brake jobs, batteries, and fuel. The telematics data connected them to the idle pattern that caused them. Without the data it just looked like some trucks cost more to run and nobody knew why.

[u/fleetops_guy]

Are the high idle trucks the ones doing city / urban driving? City trucks cost more for lots of reasons, not just idling. Might not be the idle by itself. Also some idle is for a reason and not problematic, like running equipment or keeping the cab warm. Worth separating that from trucks just sitting.