Every fleet manager has the same conversation with the same spreadsheet. The manual says service every 25,000 miles. One truck hits it in six weeks. Another takes four months. A third barely moves but idles all day at a dock. They are all on the same interval because that is the number somebody typed in when the units were bought, and nobody has had a reason to argue with it.
Then one of them ends up on the shoulder with a wheel seal that had been weeping for a month, and the reason shows up.
The interval in the OEM manual was written for an average truck. You do not run average trucks. Here is how we set a PM interval for the trucks a fleet actually runs, what moves the number, and when to move it again.
What the manual number is for
An OEM maintenance interval is a defensible middle. It assumes a typical duty cycle, typical loads, a typical share of highway miles, and a typical owner who will trade the truck before the engine is tired. It is not wrong. It is just not about your fleet.
Miles are also the wrong unit for a lot of trucks. Engine oil does not know how far the truck went. It knows how long the engine ran, how hot it got, how much fuel passed through it, and how much soot the combustion made along the way. A truck doing 10,000 highway miles a month and a truck doing 3,000 city miles with six hours of idle a day can need service on the same day, and the mileage interval will put them months apart.
So the first thing we do with a new fleet is ignore the number on the schedule and ask how the trucks run.
The four things that move the number
Idle hours. An hour at idle is roughly 25 to 30 miles of engine wear that never shows up on the odometer, and idle is where soot loading and fuel dilution in the oil climb fastest. A truck with a high idle share needs a shorter interval than its miles suggest, and it needs the interval set in hours, not miles. If your units have an hour meter, that is the number to build around.
Load and duty cycle. A regional tractor turning stop and go all day works its brakes, clutch and cooling system harder per mile than a line-haul unit cruising at 62. A straight truck making 40 stops a day puts a different kind of stress on the driveline and air system than one doing two. Heavy loads and short trips push every interval shorter. Light loads and long highway runs let you stretch it.
How the trucks get driven. Two identical units on the same route can wear at different rates because two different people drive them. Hard braking, high RPM shifting and long idle at lunch all show up in the inspection findings over time. We do not set the interval around the driver, but the findings tell us when one unit is quietly running on a different curve than its twin.
What you are trying to protect. A fleet trying to run engines to 800,000 miles services differently than a fleet trading units at four years. If you plan to keep a truck past its first life, the money you spend on shorter oil intervals early is the cheapest engine insurance you will ever buy. If the unit is gone in three years, you can run closer to the manual.
Terrain and weather, for the record, do not make the list here. The I-85 corridor through the Upstate is flat enough that it does not change wear patterns, and the weather does not change failure patterns in any way we can measure. Anybody selling you a "winter PM package" is selling you a package.
How we set it
We build the schedule to the fleet rather than dropping you into a preset tier. There is no A, B and C package here. The process is simple on purpose.
First we ask how the units run: routes, loads, idle share, hours versus miles, how long you keep them. Then we look at whatever history you have, because the last two years of repair orders will tell us which systems have been failing early. Then we set a starting interval for each class of truck in the fleet, not a single number for everything with a diesel in it.
A full service, by the way, is not an oil change with a clipboard next to it. The oil and filters are maybe a fifth of the value. The rest is the walk under the truck: brake lining and pushrod stroke at every wheel end, tire depth and pressure including the inside duals, coolant tested for freeze point and additive level rather than eyeballed, air dryer and tanks drained, belts and hoses and charge air clamps checked, steering and suspension checked for play, lights and the seven-way, DEF filter, chassis lube, and a look at anything wet that should be dry. What that walk finds is what tells us whether the interval is right. The full list is on our preventive maintenance page.
The diagnosis, done where the truck sits
Mobile service across the Upstate, the shop in Greer when the job needs a bay. If we find something, you get the number before we fix it.
When to move it
The interval is not a decision you make once. It is a number the inspection findings keep correcting.
If three PMs in a row come back with nothing marginal, the interval can stretch. If the findings keep turning up the same early wear, it needs to tighten, or that one unit needs its own schedule. If a truck's route changes, the number changes with it. The first year with a new fleet is where most of the adjustment happens. After that it settles down, and the schedule starts to feel boring, which is the point.
One more thing moves it: a scheduled PM you skip. PM is the easiest thing on the list to push a week. Then the week becomes a quarter, and the unit that missed its service is the one on the shoulder. A good interval you do not keep is worse than a mediocre one you do.
On your yard, in our shop, or both
Where the service happens does not change the interval, but it changes whether you keep it. Most fleets we work with end up running both. Scheduled PMs happen on the yard, where the trucks already sit, with no shuttle run and no queue behind somebody else's job. The work that needs a lift for a day, or needs to come apart further than a yard can support, comes to Greer. A technician who found the problem on your yard is not writing a description of it for a stranger. The unit arrives with the diagnosis done and the parts already coming.
If you are running enough units for this to be a program rather than a series of appointments, that is what our fleet PM programs page covers: set intervals, DOT tracking by unit, and one person who answers the phone.
The short version
The manual's number is a starting point. Idle hours, load, how the trucks are driven and how long you plan to keep them all move it. Set it per class of truck, not per fleet. Let the inspection findings correct it. Then keep it.
Tell us how your trucks run and we will build the schedule around it. Call 864-982-1150 or request service and we will start with a baseline pass on the yard.
Written at the counter, not in a content mill
We are a heavy-duty diesel shop in Greer. Mobile service across the Upstate, shop service in the bay on Shortie Street. If a truck of yours keeps failing the same item, call. The diagnosis and the number come before the work does.
Greer, SC 29651
864-982-1150
Mon to Fri, 8am to 5pm. After hours by arrangement.