From the headline above, you might expect that Im back on the subject of passenger car engine oil changes; but youd be wrong. This is about the upward trend in heavy duty truck engines. And boy are they a-changing! Lets walk back 40 or 50 years, to see whats changed and whats driving the changes.
Back in the 1960s we had essentially the same heavy duty engine builders that are here now. However, the hardware was a lot different.
For one thing, Detroit Diesel, a division of General Motors, had a pretty good share of the market with a two-stroke cycle engine design. These engines were durable and relatively reliable, and were found in most military vehicles (tanks, half-tracks, etc.) On the four-stroke cycle side, Cummins, Caterpillar and Mack were all in the game. John Deere, International Harvester and J.I. Case were players in the off-road market.
Engine oil recommendations at the time were for SAE 30 or SAE 40 DS quality. These oils were around 1.2 to 1.5 percent sulfated ash, and their total base number (TBN) was in the 10 to 12 range. Antiwear was provided by zinc dithiophosphate, with zinc levels at about 0.12 to 0.14 percent. By the mid-1960s, when I got into the oil industry, drain intervals were in the 15,000-mile range for the heavy duty four-strokes.
Detroit Diesels two-stroke engines were a bit different. In these engines some of the oil is always burned with the fuel, so oil consumption is pretty high. Oil makeup rates were about one quart every 200 miles. Of course with makeup rates like these, the crankcase oil was essentially replaced every few thousand miles, so it only got changed during a major overhaul or repair. In over-the-road service, the recommended drain interval was 100,000 miles!
In the four-strokes of that era, the most important driver for changing the oil every 15,000 miles was the sulfur content of No.2 diesel fuel, which was at or above 1 percent. As most of you know, when high-sulfur diesel fuel is burned, the combustion process creates a lot of sulfuric and sulfurous acid. The oils TBN will neutralize these acids but once that base is used up, the acids will do some serious damage to an engine. Bearing failures and yellow metal corrosion were a serious problem.
The engine designs at the time were based on traditional technologies, and such things as computer controls were not available. Fuel was supplied by a fuel injection system controlled by a mechanical camshaft.
By the late 1980s, long-life engine protection was the big competitive trend among oil marketers. For example, Pennzoil (my employer at the time) actually had a 1-million-mile engine oil it was pushing very hard. It was a 12 TBN, 1.5 percent sulfated ash, SAE 15W-40 product.
Moving forward in time, the next big event was the lowering of fuel sulfur for highway engines to 500 ppm maximum, in October 1993. Leading up to that, SAE Technical Committee 1 on engine oils (which I chaired then) had a semi-annual report done by an independent contractor on diesel fuel sulfur. It found the sulfur levels in the early 1990s were in the 0.5 to 0.75 percent range with occasional outliers over 1 percent. These were mostly in the Southwest United States. About a year before the new regulations became law, the sulfur levels started to drop. By the beginning of 1993, all diesel fuel was essentially in line at the 500 ppm level.
Although fuel sulfur was reduced, heavy duty drain intervals were still pegged around 15,000 to 20,000 miles. Design changes in the engines were just coming into play, but the diesel truck marketers were uncomfortable with extending drains. They believed it was cheap insurance for long engine life. (Where have we heard that before?)
As we rolled on towards the new millennium, drain intervals became a more important subject. Besides the lubricant cost and disposal issues, the downtime required to do a basic oil change meant that a truck could be out of service for most of a day. Of course, gear oil and transmission fluids were checked as well as the other basics, but no one wanted a truck out of service any longer than necessary. As any fleet owner and operator will tell you, They arent making money if theyre not rolling.
With that impetus, drain intervals were stretching out longer by the late 1990s, and development of next-generation engine oils became rapid-fire: API CH-4 oils came in 1998, CI-4 in 2002, and CI-4PLUS in 2004. While working at Chevron Oronite, I had a ring-side seat to this activity. For example, we had a field test going in Denver with mail trucks which were in continuous operation, using driver changes without shutting down the engine. The loads were below maximum weight, at about 50,000 to 55,000 pounds, but the route was over mountains and was about 7,000 miles per week. These units were running 25,000 mile drains at the time.
These oils were prototype API CI-4 products with sulfated ash content of about 1.4 percent, phosphorus levels of 0.14 percent, and TBN around 10.5. The results were exceptional and soon after – when CI-4 became the newest API category – the heavy duty OEMs began to recommend drains at the 25,000-mile mark.
The next leap in intervals came in 2006, when ultra-low sulfur diesel (ULSD) was introduced to the highway market. We were now looking at 15 ppm sulfur and the industry really started to take note of the impact on oil drains. API CJ-4 oils were introduced that year and their properties were quite a bit different from earlier oil categories. TBN was at about 10, sulfated ash was around 1 percent and sulfur levels were dropped to less than 0.4 percent.
With ULSD, which became mandatory for all highway vehicles in 2010, and improvement in fuel injection control as well as piston/ring designs, blowby acids were reduced and it became possible to lower the TBN of the oil. And again, oil change intervals took a great step forward. Since the first federal emission limits were introduced in 1974, OEMs have monitored drain intervals for their impact on exhaust systems and EPA compliance. Once those needs are covered and engine durability is assured, the only way for intervals to go is up.
The graphic below gives you an idea of how oil change intervals have grown over the last 10 years, based on current API CJ-4 chemistry. Next months introduction of API CK-4 and FA-4 category oils can be expected to push drain intervals even longer.
What else has been helping to push the envelope on drain intervals?
1) Used engine oil analysis. Most OEMs provide guidance for condition-based oil change intervals, and savvy fleet operators have taken advantage of analysis programs provided by their oil marketers or have contracted their own used oil analysis.
Used oil analysis had been successfully used by the railroads since the 1940s to monitor the condition of their locomotive engines. By the early 1960s, the trucking industry was ready for it too, and the first commercial oil analysis laboratories were born. One of the pioneers in this field is Analysts Inc. For the last 20 years, the American Trucking Associations Technology and Maintenance Council has maintained a Recommended Practice for used engine oil analysis which has seen several updates. The latest version is TMC RP 318C.
2) Driving conditions. Fuel efficiency plays a big role in oil changes since the duty cycle, routes, loads and altitude all impact the success of the vehicles operation. Operating temperature ranges such as cold starts and high ambient temps impact oil life. Driving in extreme environments such as poor quality roads, high humidity and extended idling put extra wear and tear on the oil.
I can testify to road quality after a recent drive to California. For those of you who havent driven the Phoenix-to-Newport Beach route, I-10 is a very trying experience. It is in poor condition in many places and is very crowded. Blowing dust is a regular event and the temperatures are often in the Fahrenheit 110+ range.
3) Engine properties. Fuel economy, poor seal design and heat control are all important. Emission control systems have an impact as well. Exhaust gas recirculation is particularly important as well as soot control. Of course, oil system capacity makes a difference since the more oil you have in the sump the longer it can go, especially with an efficient oil filtering system.
Similarly, engine age is also important. Several years ago, engines on the road averaged about 8 years old. Now the average has dropped to 6.5 years. That means newer engines with better operating systems, which naturally will lead to longer oil drain intervals fleet-wide, on average.
Finally, operating conditions are a key factor in raising drain intervals. Paccars MX engine for instance now recommends 60,000-mile drain intervals when fuel consumption on a unit runs at or above 6.5 mpg and less than 20 percent idle time. Could we be headed towards an annual oil change?
With such robust oils, it may become possible to construct a global oil specification. Europe and North America are becoming more harmonized in their equipment, as most North American OEMs now have a European connection (e.g. Volvo-Mack, Daimler-Detroit Diesel and now Volkswagen-Navistar).
Given this trend, by using the proper base oil, additive and viscosity modifier combination, products can now be formulated to meet 90 to 95 percent of the worlds heavy duty engine oil requirements. But thats a story for another time.
Industry consultant Steve Swedberg has over 40 years experience in lubricants, most notably with Pennzoil and Chevron Oronite. He is a longtime member of the American Chemical Society and SAE International, where he was chairman of Technical Committee 1 on automotive engine oils. He can be reached at email@example.com.