Think Thin: GF-6 Is The Latest Spec In The World of Engine Oil

Back in the ’60s, Bob Dylan wrote  “the times they are a-changin’,” and that has certainly proven to be the case with engine oil. In the last decade, there have been more changes to oil viscosity, additive packages, and synthetics than ever before and even more changes are coming.

EngineLabs has been right there at the leading edge reporting on how specific engine oil can prevent low-speed pre-ignition (LSPI). We continue that trend by bringing you updates on the industry’s push to yet another new oil spec — ILSAC GF-6. This will require a few paragraphs to fill in all the details, so put your oil-geek hat on and follow the bouncing viscosity curve.

What’s Wrong With Today’s Standards?

This most-recent push is definitely aimed at increasingly thinner viscosity oils. Congress has demanded that corporate average fuel economy (CAFE) standards will jump to the new standard of 54.5 mpg for passenger cars and light trucks, beginning in 2025. This means the current standards will increase by an average of five percent every year until 2025.

By this deadline, CAFE levels for small cars will be pushed to 54.5 mpg while trucks will be in the mid-to-high-30 mpg range. Engines will likely become smaller, using power adders like turbochargers and superchargers to achieve acceptable power levels within emissions confines. This creates a demand for low-viscosity oils to reduce friction as a step toward achieving these goals.

You may have already seen the latest ILSAC GF-6 oil splashed across the internet. This latest new-spec oil is a 0W-16 viscosity intended for 2020-year and newer vehicles. It’s really not intended to be a performance oil.

This has created a move by the automotive oil industry to create another new standard designated as ILSAC GF-6. ILSAC stands for the International Lubricants Standardization and Approval Committee. This is a committee comprised originally of GM, Ford, Chrysler (now called Fiat Chrysler Automobiles – FCA), and the Japanese car companies.

The ILSAC standards can be considered similar to American Petroleum Institute (API) standards for engine oil, which perhaps more enthusiasts are familiar with. The current API oil standard is “SN” and “SN Plus.” ILSAC has established its new standard that is further broken down to GF-6A and GF-6B, where GF-6A is equivalent to the current API SN-Plus. Confused? So were we, at first.

These are the new proposed seals for the latest API specification, "SP", which will equate to the ILSAC GF-6B specification.

Looking at GF-6

The GF-6A standard encompasses oil that ILSAC designated to be backward compatible, which means GF-6A covers the current API SN oil viscosities of 0W-20, 5W-20, 5W-30, and 10W-30. The new GF-6A standard will meet all the specifications for these current oils in addition to meeting the latest GF-6 specs.

The GF-6B category applies only to the new 0W-16 low-viscosity oil that is already being employed by Japanese and European manufacturers to meet the increasingly stringent efficiency goals. But as pointed out, this oil is not backward compatible. We take that to mean the message for enthusiasts is, “stay in your lane, bro,” which just emphasizes that even current 2019 engines are not compatible with these newest lubricants.

The current ILSAC GF-5 (SN-Plus) was originally intended to be replaced a couple of years ago, but the new GF-6 deadline is 2020. Mainly, the GF-6B standard is aimed at turbocharged, gasoline direct-injected engines tasked with achieving these fuel economy levels. Thinner viscosity oil reduces the pumping losses as well as internal friction, but also requires tighter bearing clearances inside the engine itself.

This image (courtesy of Driven Racing’s Lake Speed, Jr.) illustrates what occurs during a “mixed film condition.” When the film thickness is a bit too thin, metal-to-metal contact occurs between the microscopic peaks of the bearing journal and the bearing itself.

Thinner Than Water

Driven Racing Oil’s Lake Speed, Jr. reports that in addition to this 0W-16 viscosity, currently there is testing being done on 0W-12, 0W-8, and even 0W-4 viscosities as potential solutions to this CAFE challenge. This leads to the point that the engine oil marketplace is going to become increasingly application-specific in terms of your choice of off-the-shelf oil.

Enthusiasts already know (or should know)  that older performance engines require oils with elevated zinc and phosphate (ZDDP) levels. The reduced levels of ZDDP in current API SN engine oils demand that those with older performance engines use a different, more targeted, hot rod-style engine oil. While that hot rod-style oil doesn’t conform to current API standards, API standards weren’t created with hot rod engines in mind.

This spider diagram reveals a portion of the complex relationship additives play and how different aspects must be addressed. The attributes of GF-6A and GF-6B oils are extremely close. Both provide substantially better LSPI protections than SN-Plus engine oils.

The change to the GF-6B ILSAC standard is aimed at 2017-and-newer engines. Even the “backward compatible” GF-6A is really not intended for engines older than perhaps the latest generation of production engines – or roughly back to the mid-1990s. Older engines certainly are not compatible with these new, low-viscosity engine oils. Emphasizing this point, we found current GF-6A and B standards do not include testing on flat tappet camshaft engines because they are now considered obsolete.

It is entirely possible in the coming decades that even the ubiquitous 10W-30 may disappear from shelves at your local gas station or convenience mart because the push for newer lubricants will displace them from the shelves. While a quart of 0W-16 oil in your engine is better than none at all, enthusiasts with older engines may need to consider carrying their own supply of engine-specific oil rather than rely on a quart or two always being available at Jiffy-Mart.

Comparison of API to ILSAC Designations

API Spec ILSAC Spec Description
SP* GF-6B Not backward compatible – only forward for new engines
SN-Plus GF-6A Accommodates GDI engines
SN GF-5 Began in 2010 for turbo and high output engines
SM GF-4 2010 and older engines
SL GF-3 2004 and older engines
SJ GF-2 1996 – 2001 and older engines
SH GF-1 1992 – Not suitable for production engines after 1988
SA – SH —- Obsolete

*The API SP designation is not yet official, but is expected by 2020.

Low Viscosity Oil and Older Engines

As these newer lubricants move toward increasingly lighter viscosities, some enthusiasts may think these thinner oils can be used in earlier engines for reduced frictional losses. While a lighter viscosity will result in reduced pumping losses,  several factors work against using thinner oil unless the engine is specifically built to use low-viscosity oil.

The most important consideration is thinner oil reduces the lubricant-film thickness present between bearings and the crankshaft or connecting rod journals. This film thickness is directly proportional to the viscosity of the oil and its temperature.

We’ve included a graph from Driven Racing Oil that shows how oil thins in direct proportion to its operating temperature. For a performance engine operating at peak power, the average sump oil temperature may only be 200 degrees-Fahrenheit, but at the bearing, actual temperatures will be much higher.

This Driven Racing Oil chart indicates recommendations for a given viscosity oil based on horsepower output and average engine oil temperature. As engine oil operating temperature increases, the viscosity must also increase in order to provide an adequate oil film clearance to prevent metal-to-metal contact.

The concern is that this higher temperature will create a slightly thinner oil film and the components may touch, causing what is called mixed film lubrication. That is where the microscopic high points of the bearing and crankshaft main journal, for example, will touch each other, creating wear. This will show up as scratches or gouges in the bearing material.

Driven created a generic chart that lists average oil sump temperature and power levels that combine to list what should be a safe oil type and viscosity recommendation. Driven uses its own designations but we’ve also included a chart that lists the XP names in standard viscosity format. This chart is just a recommendation of where to start, but you can assume it to be conservative.

This graph (also from Driven Racing) reveals how viscosity changes with operating temperature. Note how at 300 degrees-Fahrenheit, there is a relatively minor difference in viscosity.

Another item to consider when choosing your oil’s viscosity is its effect on hydraulic lifters. These devices are designed to operate with a given viscosity of oil at a given temperature. Attempting to use a thinner viscosity oil may cause a hydraulic lifter to more easily pump-down, potentially sacrificing valve lift due to the higher bleed-down rate. This can also have a potentially harmful effect on newer engines utilizing variable valve timing and cylinder deactivation such as GM’s Active Fuel Management (AFM) and Dynamic Fuel Management (DFM) systems.

Something else to store in your memory banks in relationship to viscosity is that as the oil thins, pressure and volume are inversely proportional. What that means is thick oil increases the pressure and reduces the oil volume, while thinner oil will reduce the pressure and increase the volume. As long as there is a sufficient film thickness, an increase in volume will help reduce localized temperature, and thinner oil tends to run slightly cooler – assuming all other variables remain the same.

The world of automotive engine oil is becoming increasingly complicated. The days of “one-size-fits-all” engine oil are lost to history. Now, you will need to be able to speak the vocabulary of API and ILSAC if you want to keep up with what’s happening in the world of engine oil. Perhaps ‘40s actress Bette Davis said it best: “Fasten your seatbelts, it’s gonna be a bumpy ride!”

Driven Oil Viscosity by Part Number

Viscosity Synthetic Semi-Synthetic Conventional
0W XP0   —
0W-10 XP10   —
0W-20 XP20   —
5W-20 XP1   —
5W-30   — XP8 XP8
10W-30 XP3  —   —
10W-40 XP9  —   —
15W-50 XP6  — XP4
20W-50    — XP5   —

Article Sources

About the author

Jeff Smith

Jeff Smith, a 35-year veteran of automotive journalism, comes to Power Automedia after serving as the senior technical editor at Car Craft magazine. An Iowa native, Smith served a variety of roles at Car Craft before moving to the senior editor role at Hot Rod and Chevy High Performance, and ultimately returning to Car Craft. An accomplished engine builder and technical expert, he will focus on the tech-heavy content that is the foundation of EngineLabs.
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