Thicker Is Better?
By Allan W. Perry and Scott McQueen

Disproving the Myth - The Move to SAE 5W-20 Engine Oils

For most 2001 and later model-year vehicles, and even some earlier model vehicles, Ford Motor Company and Honda recommend using an SAE 5W-20-viscosity grade engine oil. This represents a change from the previous preference for heavier SAE 5W-30 and SAE 10W-30 viscosity grade engine oils. Why this change, and what is the significance to the customer?

Ford and Honda's preference for SAE 5W-20 engine oils coincided with the introduction in 2001 of API Service Classification SL and the International Lubricant Standardization and Approval Committee (ILSAC) GF-3 standard for passenger car engine oils. Both automakers established performance requirements for SAE 5W-20 engine oils that actually exceed the requirements for ILSAC GF-3. The two key driving forces behind specifying higher-quality SAE 5W-20 engine oils are improved fuel economy and improved oil performance.

IMPROVED FUEL ECONOMY

All automakers in the United States are required to meet EPA-mandated Corporate Average Fuel Economy (CAFE) targets for passenger cars and light trucks. Failure to meet these targets can result in substantial fines. Thus, automakers consider every possible source for achieving additional fuel economy, including engine oils. Lower viscosity oils generate less internal (fluid) friction than higher viscosity oils (they flow easier) leading to improved fuel economy. Using a 5W-20 instead of a 5W-30 or SAE 10W-30 oil will improve fuel economy by about 0.5 percent and 1.0 percent (absolute), respectively, over a 10W-30. Spread over just Ford's fleet of 4 million vehicles per year, this equates to fuel savings of about 100 million gallons per year. Although Honda vehicles are not in need of improved fuel economy to meet CAFE standards, Honda sees the benefits of reduced fuel consumption helping the environment by reducing the level of CO2 emissions. Honda has shown that by using a lighter viscosity grade, emissions are reduced at start-up, when cars emit most of their pollution until the catalysts come on-line.

IMPROVED OIL PERFORMANCE

Fuel economy is not the only benefit gained from using an SAE 5W-20 oil. For their SAE 5W-20-service fill specifications, both Ford and Honda have established test limits that go beyond the requirements for API SL and ILSAC GF-3. Specifically, they require a double-length ASTM Sequence IIIE or ASTM Sequence IIIF test (test run twice as many hours) with either the same (Honda) or stricter (Ford) pass/fail limits than the standard length test. The ASTM Sequence IIIE/IIIF test evaluates oil thickening, piston deposits, and valve train wear under high-speed, high-temperature conditions. In order to pass these stricter test requirements, engine oils must be formulated with high-quality base oils and very robust additive chemistry. The result is an engine oil that can deliver better oxidation stability, deposit protection, and bearing corrosion protection over a longer service interval better than previous generation engine oils and better than GF-3/SL (only) 5W-20 motor oils.

To further dispel a couple of motor oil myths, an SAE 5W-20 oil will not be more volatile or increase wear. The SAE 5W-20 motor oils adhere to the same volatility limits as do the SAE 5W-30 and SAE 10W-30 oils, as specified in ILSAC GF-3. The lighter-viscosity-grade oil also improves wear protection by being able to pump faster within an engine. This means that it will reach the necessary lubrication areas quicker than thicker oils and protect during the critical period of startup. In short, these oils provide longer oil life and better overall engine protection. Due to these many performance advantages, the recommended viscosity grade for many passenger cars has gradually been lowered over the past several years from SAE 10W-30 to SAE 5W-30 and now to SAE 5W-20 for most Ford and Honda vehicles. This trend is expected to continue as witnessed by Daimler-Chrysler, who recommended SAE 5W-20 for most of their 2005 model year vehicles.

WHY USE AN SAE 5W-20 ENGINE OIL?

Ford, Honda and Daimler-Chrysler's recommendations for SAE 5W-20 engine oils are based not just on the desire for higher quality, more fuel-efficient engine oils, but are backed up by extensive dynamometer and fleet testing to demonstrate performance and engine protection. The newer engines are engineered to deliver optimum performance using an SAE 5W-20-viscosity grade engine oil. Using a higher-viscosity oil could compromise eng

ine performance over the long term and could be grounds for voiding the manufacturer's warranty if warranty issues should arise. It is important to remember that API Service Classifications, ILSAC standards, and OEM (Original Equipment Manufac

Allan W. Perry is technical specialist, and Scott McQueen is director, automotive products for ConocoPhillips Lubricants - Conoco, Phillips 66, 76 Lubricants and Kendall Motor Oil - headquartered in Houston, TX.