Fluids, Filters, Lubrication, and Safety Compliance
The right fluid, the right record
Fluids and filters are where shortcuts become failures. Every fluid on the bus has a specification: engine oil meeting the OEM's API category, transmission fluid approved for that transmission (an unapproved fluid can destroy a retarder-equipped automatic), the correct gear lubricant for the differential, ISO 22241 DEF, and coolant of the right chemistry. OAT and conventional coolants do not mix; combining them can gel and plug the heater core and radiator. When the correct product is unknown, stop and find out rather than topping off with whatever is on the shelf.
Filters are matched to micron rating and application: full-flow lube, fuel/water separator, air filter, transmission, coolant if fitted, and hydraulic. Record part number and date on the work order. Used oil, filters, coolant, and batteries are regulated wastes; keep them in labeled containers and know where the spill kit is.
Safety compliance is examinable. Lockout/tagout comes before servicing anything with stored energy, including air systems and the electrical disconnect. Never inflate a truck tire outside a restraining device or with the wheel assembly unbolted. Use cribbing and stands, not a jack alone. Wear eye and hand protection, and follow right-to-know for chemicals.
Worked rule of thumb: service intervals are whichever comes first, mileage or time. A bus running only 900 miles a month still needs its time-based PM.
Trap: adding the correct volume of the wrong fluid is still a failure.