The Difference Between Synthetic and Conventional Oil in Trucks

What Is Conventional Oil?

Conventional oil, often referred to as mineral oil, is refined from crude petroleum. After undergoing distillation and purification, it’s treated with additives to enhance its basic lubricating properties. It’s been the standard lubricant for internal combustion engines for decades and is typically less expensive than synthetic alternatives.

Characteristics of Conventional Oil:

• Derived directly from natural crude oil
• Offers adequate protection for light-duty applications
• Tends to break down faster under extreme heat or heavy loads
• Requires more frequent oil changes in heavy-duty engines

In diesel trucks, conventional oil provides lubrication, helps reduce wear, and removes contaminants via the oil filter. However, due to its molecular inconsistencies, it’s more prone to sludge formation and viscosity breakdown under intense working conditions.

What Is Synthetic Oil?

Synthetic oil, on the other hand, is engineered from chemical compounds, resulting in a lubricant with uniform molecular structure and superior properties. Whether fully synthetic or synthetic blend, these lubricants are crafted to perform under higher thermal and mechanical stress.

Key Benefits of Synthetic Oil:

• Greater resistance to oxidation and thermal breakdown
• Better flow in cold temperatures and high-pressure situations
• Longer oil change intervals, reducing service downtime
• Enhanced protection against engine wear and sludge buildup

Synthetic oil excels in high-mileage diesel engines, severe duty cycles, and extreme temperatures, making it an ideal choice for fleet vehicles running long hauls or towing heavy loads across mountainous terrain.

Comparing Performance in Diesel Engines

Lubrication and Engine Wear

Synthetic oil provides more stable viscosity across a wide temperature range. In cold starts, it flows faster, reaching critical engine components before metal-on-metal contact can occur. This reduces startup wear—one of the leading causes of long-term engine damage.

Conventional oil, while still effective, thickens in lower temperatures and thins out under sustained high heat. This inconsistency in viscosity leads to:

• Greater friction
• Increased engine wear

Engine Cleanliness

Synthetic oil generally includes superior detergent and dispersant additives, helping prevent sludge and varnish deposits. These deposits, if unchecked, can clog oil passages, affect turbocharger performance, and hinder the function of emission systems like the Diesel Particulate Filter (DPF) or EGR valve.

With conventional oil, these contaminants build up more readily, requiring more aggressive preventive maintenance and potentially contributing to emissions system failure.

Oil Change Intervals

Trucks using synthetic oil often enjoy extended oil change intervals—up to 25,000 miles in certain applications. Conventional oil, by contrast, typically requires service around every 10,000 to 15,000 miles, especially under heavy loads or extreme operating conditions.

While synthetic oil may carry a higher upfront cost, it provides longer service life and reduces the frequency of maintenance-related downtime.

Fuel Economy

Synthetic oil reduces internal engine drag thanks to its stable viscosity and lower friction coefficient. This can lead to slight but meaningful gains in fuel efficiency, especially over thousands of highway miles.

Although conventional oil may not negatively impact MPG in the short term, its lower efficiency becomes more pronounced in Class 7 and Class 8 trucks operating under stress, particularly on steep inclines or during extended idling.

Compatibility and Application Considerations

Not all engines are created equal. Some older diesel engines, particularly those not built to modern emissions standards, may have tighter tolerances or seals that respond better to the thicker properties of conventional oil. That said, many of today’s heavy-duty engines are engineered to run cleaner and longer with synthetic oil.

When making the switch to synthetic oil, particularly in older engines, it’s wise to monitor for seal shrinkage or leaks, as synthetic oil’s detergent properties may clear away sludge that was artificially sealing small gaps.

Cost Analysis: Upfront vs. Long-Term

The initial cost of synthetic oil is undeniably higher—often 2 to 3 times the price per gallon compared to conventional. However, when factoring in:

• Longer drain intervals
• Reduced labor costs
• Lower risk of mechanical failure
• Improved fuel efficiency

…it becomes clear that synthetic oil offers superior long-term value, particularly for fleet owners or long-haul operators looking to optimize their total cost of ownership (TCO).

When to Use Each Type

Choose Conventional Oil When:

• Operating older engines with significant mileage
• Running shorter, low-load routes
• Budget constraints override long-term ROI
• Following manufacturer recommendations for specific engine models

Choose Synthetic Oil When:

• Operating under heavy loads or in high-temperature environments
• Running newer engines that demand tighter emission control
• Seeking extended service intervals and reduced maintenance
• Operating in cold climates with frequent cold starts

Choose the Right Oil Today

Synthetic oil offers unmatched protection, extended intervals, and improved fuel economy—ideal for the mountainous terrains and rigorous hauls. Conventional oil, while still reliable, is better suited to lighter-duty or legacy engines with more modest demands.

If you require truck oil services near Mt. Nebo and Sutton, WV, reach out to our team at AMF Enterprises today.