Automotive Lubricants

Viscosity Continues to Decrease


Viscosity Continues to Decrease


I know that many of you are tired of hearing me say that viscosity is the single most important property of any oil. It’s a mantra I learned as a rookie in the oil industry and one that I believe. The thing is, how do we know which viscosity is the correct one? For over one hundred years there has been an SAE standard, SAE J300, that provides a relatively easy way to help the end user choose. However, in most cases the end user needs guidance on what viscosity is right for their application.

I usually go back in time to lay the groundwork for my comments, but this time I’ll refrain. Besides, if you’ve saved your old copies of Lubes’n’Greases you can probably find one or two columns that go over viscosity in more detail. There is a story about viscosity that I would like to delve into that concerns the decrease of viscosity over the past at fifty years.

When I started working at Pennzoil in 1979, the API category system was already in place. At that time, API SE was the current performance category. Unlike today’s API categories, no distinction was made about viscosity. Whether it was SAE 10W or SAE 50, the same performance limits were set. At that time, there was no real industry information about which oils were sold and which viscosities were popular. To top it off, do-it-yourselfers made up about 80% of the market. Do-it-for-me’s—those folks who had someone else do the work—were a distinct minority. Oil changes were done based on the famous (or infamous) 3-month, 3,000-mile interval recommendation.

Source: American Fuel & Petrochemical Manufacturers (1) Combined with 10W to comply with “three respondents rule” (2) Not reported separately (3) Not identified separately before 1982 (4) Separated in 1982 (5) Combined with 5W-20 to comply with“three respondents rule” (6) Included in “not classified” (7) Category deleted (8) Combined with 5W-30 (9) Combined with 15W/20W-50 (10) Combined with “other” (11) Included in total
Monograde (Thousand Gallons)
0W and 5W669(1)(10)(2)(2)(2)
20W and 20W-2050,9059,5465,651(2)180500
Not classified25,81123,80123,083(2)00
Total Monograde521,408381,795314,763153,729111,13053,200
Multigrade (Thousand Gallons)
Not classified15,57719,10219,77233,534(2)101,000
Total Multigrade482,294700,217824,970886,8471,231,400958,400
Grand Total1,003,7021,082,0121,139,7331,040,5761,342,5301,011,600

Being the numbers guy that I am, I started looking around for data. I was interested in what volumes of oil were sold and their viscosities. The National Petroleum Refiners Association—NPRA, which is now known as the American Fuel & Petrochemical Manufacturers—was collecting that sort of data and began reporting it for the first time for 1980. That went on annually until 2006 when the NPRA ended the practice. The way it gathered data was to ask individual marketers and refiners to share the data (coded) that was then compiled and reported.

I did some numerical magic on the NPRA numbers, which showed a lot of changes over the 25 years’ worth of data. Some of the more interesting results are reported below:

  • The total volume of engine oils was close to one billion gallons annually and surprisingly didn’t change very much. I must assume that two forces were at work here, the first of which being that the VIO (vehicles in operation) was growing at the same time that crankcase volume was decreasing.
  • Oil quality was increasing. The main API category in 1980 was API SE. By 2005, we had advanced to API SL. The ILSAC designations (GF-1, GF-2, etc.) came later, starting in 1992. By 2005, the ILSAC designation was GF-3. Remember that each improvement—SX or GF-X—was backwards compatible, meaning the newer oil would be an acceptable substitute for an earlier category.
  • Engine oil viscosity was going down. I base this observation on the relative oil volumes by viscosity grade. The largest volume in 1980 was SAE 30!  The largest multigrade volume was SAE 10W-40. By 2005, the largest volume was SAE 10W-30, which was closely followed by SAE 5W-30 and SAE 15W-40.
  • The relative volumes of monograde and multigrade oils changed dramatically. In 1980, monograde and multi-grade were even in volume. By 2005, monograde accounted for 5% and multigrade for 95%.

As a professor in my college days used to say, “It should be obvious to the most casual observer” that something was driving these changes. I won’t keep you guessing: It was the OEMs dealing with emission and fuel economy directives from the federal government that pushed viscosity down. Viscosities were going down, oil quality was being improved and oil change intervals were being extended. 

Vehicles in operation include passenger cars and light trucks (pickups and SUVs).  In 1980, there were about 150 million in the United States—split at 85% passenger cars and 15% light trucks. By 1990, there were approximately 182 million total, with light trucks accounting for 26% of the total. The year 2000 saw 213 million total vehicles, with light trucks accounting for 37%. The 2005 data show the same progression. In fact, the VIO was 247 million in 2005. The number of light trucks was about 40% of that total. Fast forward a few years and 2020’s VIO was in the 285 million range, with more light trucks than passenger cars. The 2020 VIO is hovering around 290 million and the light truck category now accounts for over 50%.  The bottom line here is that there are more vehicles using more robust oil formulations with lower viscosities.

API, which licenses ILSAC GF-6, has asked the Auto/Oil Advisory Panel (AOAP) and the API Lubricants Group to add two new viscosity grades, SAE 0W-8 and SAE 0W-12, to ILSAC GF-6B. GF-6B currently includes only SAE 0W-16.

AOAP will evaluate the request. Given that it accepts it, the new grades will be added to GF-6B using API 1509, Annex C procedures. Changes to API SP, the latest API gasoline engine oil standard, will be handled by the API Lubricants Group in parallel with any changes in the ILSAC GF-6 specification. 

Jeffrey Harmening, API senior manager, noted that the new viscosity grades can be fast tracked for quick approval and incorporated into GF-6B by the end of 2022. However, there is a fly in the ointment. A current GF-6 fuel economy test (Sequence VIF) hasn’t demonstrated the ability to accurately measure fuel economy for these ultra-low-viscosity grades. To address this, API is recommending that a new fuel economy test standard from the Japanese Automotive Standards Organization, known as JASO, be added. The test standard is JASO M366 – Automobile Gasoline Engine Oils – Firing Fuel Economy Test Procedure.

The bottom line here is that there are more vehicles using more robust oil formulations with lower viscosities.

 JASO M366 is a fired engine test that measures fuel consumption using very low-viscosity gasoline engine oils. JASO M366 is available at United States independent labs and has some base oil interchange and viscosity grade read-across guidelines. API plans to add this test to GF-6 in a manner to be determined by the AOAP.  Test limits will be set using current JASO methodology.

For background, these grades were proposed for GF-6 but were not pursued since they were not available in SAE J300. They were added to J300 in 2015, but GF-6 development and introduction would have been delayed even more than it already had been. Adding them now would cover the gap in very-low-viscosity grades globally. In addition, there wasn’t a test procedure available for evaluating fuel economy for low-viscosity engines oils. The JASO procedure covers that issue as well.

So, very-low-viscosity engine oils will be available as ILSAC GF-6B as well as API SP. Why does this matter? Fuel economy and exhaust emissions are driving the boat as usual. Very-low-viscosity means lower frictional drag within the engine, which translates into less energy required to operate. Less energy used means fewer emissions. I’m sure that some of you are thinking that the viscosity is so low that it doesn’t protect adequately against wear. That doesn’t seem to be a problem, since we’ve been running vehicles on pretty low-viscosity oils for quite some time. My view is that additive technology has partially solved that gap, and the addition of partial or fully synthetic base oils has aided in the performance improvements we’re seeing today, too.

The SAE 0W-20 viscosity is more common now. My 2020 Honda Pilot specifies SAE 0W-20, and I live in Arizona. In addition, I have the 3.5 L V-6 engine option, which is a mainstay of the industry. I don’t drive as much as I used to, but in 115°F temperatures and in city traffic, the engine stays cool and fuel economy is about 24 miles per gallon. I guess you can identify the fact that in 1980 SAE 30 was the top dog viscosity-wise. Now the SAE 0W-XX grades are the leaders and growing. I wonder what the bottom line on viscosity might become.  

Steve Swedberg is an industry consultant with over 40 years experience in lubricants, most notably with Pennzoil and Chevron Oronite. He is a longtime member of the American Chemical Society, ASTM International and SAE International, where he was chairman of Technical Committee 1 on automotive engine oils. He can be reached at