The Ultimate Guide to Semi Truck Maintenance

Engine and Aftertreatment System Maintenance

Diesel Engine Service

The diesel engine is the power center of every semi truck. It requires routine inspections, oil and filter changes, and coolant flushes. Pay close attention to:

• Engine oil: Change at OEM-recommended intervals to preserve internal component integrity.
• Coolant systems: Test and flush regularly to prevent overheating and scale buildup.
• Fuel filters: Replace consistently to protect injectors and prevent loss of fuel pressure.

Neglecting engine maintenance will directly affect efficiency, increase emissions, and eventually lead to catastrophic engine failure.

Aftertreatment Components

Modern emission systems are intricate and sensitive. Semi trucks typically include a Diesel Particulate Filter (DPF), Selective Catalytic Reduction (SCR) system, and Diesel Exhaust Fluid (DEF) system. Preventative steps include:

• Monitoring DPF for passive or forced regens.
• Keeping the DEF tank full with high-purity urea mixture.
• Cleaning or replacing EGR coolers and valves to maintain NOx reduction performance.

Routine scanning of the ECM (Engine Control Module) will help detect emerging emission issues before they become downtime events.

Transmission and Driveline Care

Transmission Systems

Whether manual, automated manual, or automatic, transmission systems require routine fluid checks and inspections of clutch or torque converter components. Best practices include:

• Monitoring fluid color and consistency.
• Adjusting clutches on manual units.
• Watching for symptoms like hard shifting or gear slippage.

Overheating and metal shavings in the fluid are early signs of failure that must not be ignored.

Driveshafts and Differentials

The driveline transmits engine torque to the wheels. This includes driveshafts, U-joints, differentials, and axles. A failed driveline component can immobilize the truck or cause damage to surrounding systems.

• Check U-joints for play and ensure they are well-lubricated.
• Inspect differential fluid and change per OEM specifications.
• Monitor for signs of bearing failure like screeching or overheating hubs.

Brake System Maintenance

Air Brake Components

Heavy-duty vehicles use compressed air braking systems. Critical components to maintain include:

• Air compressors and air dryers: Moisture in the system can lead to corrosion and winter freeze-ups.
• Brake chambers, slack adjusters, and S-cams: Inspect for wear and correct pushrod stroke.

A failure in the braking system is not just costly—it's dangerous. Proper brake adjustment is a legal requirement and a key part of roadside inspections.

Preventive Brake Checks

• Perform leak tests during pre-trip inspections.
• Verify that tanks are holding pressure at 100–125 PSI.
• Replace worn brake shoes before they reach legal minimums.

Suspension and Steering System

Semi truck suspensions absorb shocks and carry heavy loads, while steering systems ensure precise control.

• Leaf spring setups should be inspected for cracks or sagging.
• Air suspension systems require airbag integrity and leak detection.
• Shock absorbers and torque rods should be inspected for wear.

On the steering side, ensure power steering fluid is topped off and inspect for loose tie rods and drag links.

Electrical System Checks

Modern trucks rely heavily on electronics—from ECMs to lighting and sensors. Poor grounding or corroded wires can trigger fault codes and shut down vital systems.

• Inspect batteries, terminals, and wiring harnesses regularly.
• Test alternator output to ensure charging system health.
• Use a multimeter to identify voltage drops in circuits prone to corrosion.

Coolant System

Heavy-duty coolant systems include radiators, fans, thermostats, and coolers for oil and transmission fluid.

• Flush and refill coolant based on manufacturer specs.
• Inspect fan clutch operation and belt condition.
• Pressure test the system to locate potential leaks or weak hoses.

Engine overheating is a leading cause of roadside breakdowns and often preventable with disciplined maintenance.

Tire and Wheel Maintenance

Tires are a major expense and a leading cause of roadside service calls.

• Maintain correct tire pressure using TPMS if available.
• Rotate tires to even out wear patterns.
• Inspect for irregular wear, sidewall damage, and embedded debris.

Wheel-end inspections should include checks of hub oil, seals, and bearings to prevent failure.

Scheduling and Documentation

Maintenance Scheduling

A preventive maintenance (PM) schedule is the backbone of fleet uptime. This includes:

• A-service every 10,000–15,000 miles: oil change, lube, basic inspection.
• B-service every 30,000 miles: comprehensive check including brakes, belts, and hoses.

Use digital fleet software to track PMs, parts usage, and technician notes.

Record Keeping

Keep detailed logs of all maintenance activities:

• Date and mileage of service.
• Components serviced or replaced.
• Technician signatures and parts used.

Proper documentation ensures DOT compliance and protects against litigation in the event of an accident.

Stay Ahead of Costly Repairs

Semi truck maintenance is not a luxury—it's a necessity. Proper attention to your engine, transmission, braking, and electrical systems ensures regulatory compliance, extends vehicle lifespan, and reduces the risk of unplanned downtime.

For those who want to minimize downtime, contact Amoretti Diesel Repair in St. George, UT, today to schedule your next inspection.

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