The Essential Guide to Choosing Heavy-Duty Engine Oil for Trucks and Buses

Heavy-duty trucks and buses operate under extreme conditions such as long hours, heavy loads, frequent stop-start cycles, and often high ambient temperatures. Choosing the right engine oil is not just a maintenance decision; it impacts engine life, fuel efficiency, uptime, and operating costs.

This guide breaks down what engine oil is recommended for heavy-duty trucks and buses, how to select the right specifications, and how oil analysis programs can help fleets make smarter maintenance decisions.

Understanding Heavy-Duty Truck and Bus Engines

Unlike diesel light duty passenger vehicles, heavy-duty diesel engines are designed for severe operating condition. The engines expected to generate higher combustion pressures, operate at elevated temperatures, and are often expected to deliver consistent performance over hundreds of thousands of kilometres.

Because of this, heavy duty engine oil is expected to:

• Handle heavy loads and high soot levels
• Provide sufficient wear protection
• Maintain viscosity over engine oil drain interval
• Protect modern after-treatment systems

Why Choosing the Right Engine Oil Matters

Using the wrong engine oil — or an oil that does not meet engine manufacturer or API requirements — can lead to:

• Accelerated engine wear
• Sludge and deposit formation
• Reduced fuel efficiency
• Shorter oil drain intervals
• Higher maintenance and downtime costs

For fleet operators, this translates directly into lost revenue and higher total cost of ownership.

Recommended Engine Oil Types for Heavy-Duty Vehicles

Most heavy-duty trucks and buses run on diesel engine oils specifically formulated for commercial vehicles. These oils are engineered to manage soot, neutralise acids, and maintain protection under severe operating conditions.

High-performance heavy-duty engine oils typically offer:

• Excellent oxidation stability
• Strong detergency and dispersancy
• Proven wear protection under high loads

Caltex Delo heavy-duty engine oils and ancillary lubricants are formulated to meet these demands, helping fleets maintain engine cleanliness, durability, and reliable performance across varied operating conditions.

Choosing the Right Viscosity Grade

Viscosity grade plays a critical role in engine protection and efficiency.

Common viscosity grades for heavy-duty trucks and buses include:

• SAE 15W-40 – Widely used for its balance of protection and performance across diverse operating conditions
• SAE 10W-30 – Often chosen for improved fuel efficiency and cold-start performance

The correct viscosity depends on:

• Engine design and OEM recommendations
• Local climate and environment
• Duty cycle (long-haul vs stop-start urban operation)

Using the right viscosity helps ensure proper lubrication, wear protection, and optimal engine efficiency.

Key Factors to Consider When Selecting Engine Oil

When choosing engine oil for trucks and buses, fleet operators should consider:

• Engine age and technology (older engines vs modern low-emission engines)
• Operating environment (heat, dust, stop-start driving)
• Load and duty cycle
• Desired oil drain intervals
• Maintenance strategy and cost targets

A one-size-fits-all approach rarely works for mixed fleets.

Caltex Delo Products for Trucks and Buses

When it comes to heavy-duty diesel engines, one principle is paramount: reliability. Achieving this requires more than just a simple protective film between moving parts. It demands a lubricant engineered for the complex challenges inside a modern engine.

Caltex Delo® heavy-duty engine oils are formulated to deliver this essential reliability. They provide advanced soot dispersancy, robust wear protection, and effective sludge control. This comprehensive defence is crucial to guarding against premature loss of engine life and can contribute to reductions in both fuel and oil consumption.

The performance and integrity of Caltex Delo products are rigorously proven through extensive bench testing, meeting and exceeding the industry's toughest standards. This proven performance is why Caltex industry-leading lubricants have logged countless hours in the real world, delivering dependable protection to critical diesel engine parts across vast fleets of heavy-duty vehicles.

Delo Protects Trucks

Delo Protects Buses

Products

Engine oils

• Delo® Gold Ultra SAE 15W-40 – Multigrade, API CI-4/SL heavy duty engine oil for trucks, buses and engines without after treatment system
• Delo® 400 MGX SAE 15W-40 – Multigrade, API CJ-4/SM heavy duty engine oil for trucks, buses and modern diesel engines that require low saps engine oil
• Delo® 400 SLK SAE 15W-40 – Multigrade, API CK-4/SN heavy duty engine oil for trucks, buses and modern diesel vehicles with or without after treatment systems that require low saps engine oil
• Delo® FleetPro SAE 15W-40 – Multigrade, API CH-4 heavy duty engine oil for trucks and buses.

Transmission fluids

• Delo® Syn ATF XV - is optimized for efficiency‑focused applications, delivering smooth, consistent shifting and improved energy efficiency through its low‑viscosity, high‑stability formulation that performs reliably across a wide operating temperature range.
• Delo® Syn ATF HD – Sis engineered for severe‑duty service, providing exceptionally long drain intervals and robust protection against wear, sludge, and varnish by using a highly oxidation‑resistant synthetic formulation designed for extended, high‑load operation.

Gear lubricants

• Delo® Syn-Gear XDM SAE 80W-140 – Synthetic heavy duty, extreme pressure extended drain gear lubricant recommended for Dana and Meritor axles and differentials operating under severe conditions in trucks and buses.
• Delo® Gear ESI® – Long drain gear oils with ISOSYN® technology for use in axles and differentials of trucks and buses operating under severe temperature and load conditions.

Coolants

• Delo® XLC Antifreeze/Coolant – Long life antifreeze/coolant for trucks and buses requiring a nitrite-free coolant.
• Delo® ELC Antifreeze/Coolant – Also a long-life antifreeze/coolant for trucks and buses requiring a nitrite containing coolant.

Greases

• Starplex EP - Premium, multipurpose EP automotive wheel bearing and chassis grease.
• Multifak EP - Extreme pressure multi-purpose grease for trucks and buses.

Keep Your Fleet Running Longer

Managing a fleet of trucks, buses, or coaches is a constant challenge. These vehicles must operate daily to maintain profitability, making their reliability non-negotiable. We support that operational imperative by providing high-quality Caltex products and services designed to keep your fleet moving forward and running longer.