Ask the Expert: The Link Between Engine Oil and Fuel Efficiency

Evolving fuel efficiency and regulatory standards are requiring vehicles to burn less energy and reduce emissions. One of the tactics used to address these requirements is the strategic selection of engine oil. The harder your engine works, the more fuel it has to burn to compensate for the energy lost through heat and friction.

When this loss of fuel persists over years of driving, it adds up to a significant financial loss. The right oil will reduce friction by optimally lubricating contact points so that components don’t require as much energy to run smoothly. An interview with CITGO Senior Product Specialist, Steven Bowles, reveals how CITGO’s 10W-30 heavy duty engine oil is helping both on and off-road vehicles conserve fuel, save costs, and meet efficiency demands.


Q: In layman's terms, how does CITGARD 10W-30 improve fuel economy?

A: Viscosity is one of the most important properties of an engine oil.  Basically, viscosity is how thick or thin the oil is and how easily it flows.  Lower viscosity engine oils are thinner and flow more easily than higher viscosity oils. 

During operation, it takes less energy for an engine to pump low viscosity oils than high viscosity oils.  Picture two swimmers racing each other, and one is swimming in water and the other is swimming in honey.  Which swimmer is going to have a harder time and spend more energy?  The one swimming in the thicker fluid.  The key to engine oil is that it has to be the right viscosity to maintain an effective fluid film between parts, but not too thick of a film to cause energy loss. 


Q: On average, what percentage of fuel savings does CITGARD 10W-30 offer over conventional higher viscosity oils?

A: CITGO has a Guaranteed Efficiency Program (GEP) that guarantees a fleet at least 1.5% increase in fuel efficiency, up to 3% when switching from a 15W-40 engine oil to one of our 10W-30 or 5W-30 heavy duty engine oils.  We have many fleets that have participated in this program and achieved these results or higher.


Q: Emission standards set quantitative limits on the permissible amount of specific air pollutants that may be released from specific sources over specific timeframes. As these standards are becoming stricter, how is CITGARD helping vehicles meet these requirements?               

A: With regards to Green House Gases (GHG), namely CO2, the main way to reduce CO2 emissions is to burn less fuel (increase fuel economy).  CITGO's CITGARD 10W-30 and 5W-30 engine oils help increase fuel economy and lower CO2 emissions.  CITGARD Engine oils also help keep engines clean and running efficiently, which can help reduce particulate matter (PM) emissions.


Q: Which additives play the biggest role in improving fuel efficiency?

A: All the additives in the CITGARD engine oils help contribute to fuel economy since engine oil formulations require a well-balanced formula.  If you over-treat in one area such as anti-wear, another area such as corrosion protection may suffer. That is a major reason why after-treatment additives are not recommended, since they tend to focus on one additive area and can alter the balanced engine oil chemistry. 

CITGARD engine oils do have excellent anti-wear protection - which protects engine components and helps keep the engine running longer, and antioxidants - which keep the oil from oxidizing and thickening up, allowing fuel economy benefits to be maintained throughout the oil drain interval.

CITGARD engine oils also have high TBN (Total Base Number) to help neutralize acids produced during combustion and a balanced detergent package with both Calcium and Magnesium detergents to keep parts clean and the engine running efficiently.


Q: Is this oil best suited for newer engines? Can off road applications benefit from this oil just as much as on road vehicles?            

A: API currently has two heavy duty engine oil categories, CK-4 oils, which are backwards compatible and can be used in both newer and older engines, and FA-4 oils, which are typically for newer (2017 or later) engines, but can be used for some older engines depending on the engine manufacturer. 

It is always best to check your owner's manual to determine the appropriate engine oil.  Most over-the-road trucks are currently factory-filled with either CK-4 or FA-4 10W-30, depending on the manufacturer.  Off-Road manufacturers tend to fill with either CK-4 10W-30 or 15W-40. If recommended by the manufacturer, 10W-30 engine oils can also save fuel in off-road applications.


Q: The condition of the engine undoubtedly plays a significant role in its performance, and therefore fuel efficiency of the vehicle. How does CITGARD 10W-30 provide advanced wear protection to maintain engine health compared to alternative oils?         

A: CITGO has performed testing and field trials where results showed the wear metal levels with CITGARD 700 Synthetic Blend 10W-30 are well below condemning limits even at drain intervals of 60,000 - 90,000 miles or more. We have field trial data with a fleet that used the CITGARD 700 MFE Synthetic Blend 10W-30 (FA-4) on a truck that went 850,000 miles at 75,000 mile drain intervals and the parts looked terrific when the engine was examined. 

As mentioned earlier, it's not just the wear protection, but the engine formula as a whole that provides for a clean, efficient engine.  We have data that shows new oil with a 2% fuel economy improvement and the aged in-service oil at 50,000 miles still maintaining close to the same fuel economy.


Q: Do you have any testimonials or real cost saving metrics from any of your customers since switching to 10W-30?

A: Brundage Bone, the largest concrete pumping company in the United States, was able to save 2 - 2.5% annual fuel cost savings after switching from 15W-40 to CITGARD 700 Synthetic Blend Heavy Duty Engine Oil SAE 10W-30. 

This is a good example of a fleet that's not an over-the-road fleet that is also able to save money by switching to CITGARD 700 Synthetic Blend 10W-30.  We have several over-the-road fleets that are averaging around 2 - 3% fuel efficiency.


Although much can be done to improve fuel efficiency (maintain your tire pressure, avoid excessive idling, etc.), switching to a lower viscosity engine oil like the CITGARD 10W-30 is one of the easiest tactics. Formulated to provide an optimal barrier between engine components, you can average 2 – 3% annual fuel cost savings while reducing emissions and maintaining the health of your engine.

For more information on CITGARD engine oils, visit


Steven Bowles is an experienced Senior Product Specialist with a demonstrated history of working in the oil & energy industry. He is skilled in Petroleum, Environmental Compliance, Environmental Awareness, Manufacturing, and Petrochemical. In addition to earning a Master of Science focused in Environmental