• Lubricate the engine
• Control wear
• Control sludge and deposits
• Handle soot
• Neutralize acid and control corrosion
• Cool critical engine parts
• Maintain seals

In addition to all these things, though, the engine oil itself must maintain its vital performance characteristics. “It has to resist change in viscosity, so that it doesn’t go too much above or too much below its intended and designed grade,” Pettingill said. “It has to control oxidation, which is more important now that engines are running hotter than they used to. It has to resist volatility at high temperatures, so that it stays as a liquid and doesn’t go into the vapor state. Above all, it has to maintain its function at wide temperature ranges. Multi-grade oils have to protect at very low temperatures as well as very high temperatures.”

So why does the industry need lower-viscosity heavy-duty engine oil? 

“Lower-viscosity engine oils enable improved fuel economy,” Pettingill said. “The lowest viscosity currently allowed for API-licensed and OEM-approved heavy-duty diesel engine oils in the North American market are the API FA-4 products. They’re available as 5W-30 and 10W-30 viscosity grades, and they’re defined by their high thermal, high shear limits of 2.9 to 3.2 centipoise. Your HTHS is a simulation of viscosity at high temperatures under extreme loading conditions.”

In comparison, more traditional heavy-duty engine oils must have an HTHS of 3.5 cP or higher, depending on the oils’ viscosity grade or OEM requirements. “So in some cases, those minimum requirements are 4.2 for, say, a 15W-40,” Pettingill said. 

In addition to increased fuel economy, Pettingill said that lower-viscosity engine oils that maintain engine protection reduce vehicle operating cost and improve vehicle exhaust emissions. “You’re burning less fuel, so that is less emissions” he said.

How do we know this to be true? 

“Within the engine oils business, there is general industry acceptance and agreement to the correlation of engine oil viscosity with fuel consumption and that lower-viscosity engine oil enables improved fuel economy,” Pettingill said. “Even in the case of FA-4 oils, which were launched at the same time as the most recent category of CK-4, there was no actual fuel economy test that you had to run to demonstrate fuel economy capability of the FA-4 oils because the industry consensus is very strong. So where you have a higher grade with a higher HTHS, you will use more fuel in comparison with a lower grade having a lower HTHS.” 

Bring on the Prototypes

“The challenge to us is, can we formulate a heavy-duty engine oil with viscosity below SAE 30 and FA-4 limits and still provide strong engine protection?” Pettingill said. 

In answer, Petro-Canada Lubricants developed two prototype 0W-20 heavy-duty diesel engine oil formulations for field trial evaluations. No 0W-20 heavy-duty engine oil formulations are commercially available in the North American market. 

“Viscosity grade is defined by kinematic viscosity at 100 degrees Celsius,” Pettingill explained. “So the traditional grades that you’re probably used to seeing are 5W-40, 15W-40 or 10W-40, which are higher viscosity. There’s been a recent industry acceptance and OEM approval of the SAE 30 grade. We are testing even lower to enable improved fuel economy in the SAE 20 region.” 

However, certain formulation challenges come along with low-viscosity engine oils. “It’s not that easy,” Pettingill said. “You don’t want to just go into a test program or into a field trial without really giving some thought as to what you need to still protect the engine.” 

Petro-Canada’s main formulation concerns were the low HTHS values of the oils, as they could risk oil film strength required to protect critical engine parts. It was also concerned with the low base oil viscosity because it was also a potential risk to film strength that could increase volatility of the oil under high operating temperatures. 

“The risk has been alleviated in part with the use of proven performance additive technology that is common to API CK-4 products,” Pettingill said. “You go ahead and design the oil, but it’s a very novel approach, so the prototype 0W-20 oils were very carefully monitored with frequent sampling and testing through our used oil analysis program to check for critical performance characteristics during the fuel trial. You want to make sure that these oils are going to hold up.”

Testing and Results

Prior to testing, both the 0W-20 prototype oils were assigned test codes to prevent potential bias. The new oils were referred to as Test Oil Grey and Test Oil Beige. The two different 0W-20 formulations shared some similar formulation characteristics; both had the same base oil viscosity targets and the same kinematic viscosity. Both oils were also formulated using Group III base oils as well as the same additive package. 

The oils differed in the type of viscosity modifier used. “Test Oil Grey has a comb polymer, while Test Oil Beige has a star polymer,” Pettingill said. “Otherwise, the physical characteristics of what needs to be 0W-20 viscosity requirements are very similar.”

The test conditions were severe, Pettingill said. “They were really put to a severe test because we feel that if they can make it under really heavy conditions, then lighter loaded conditions shouldn’t be a problem,” he said. 

The trucks used for testing were ProStar International trucks equipped with Navistar MaxxForce N13 engines. The routes were long-haul routes with maximum loading of up to 140,000 pounds gross vehicle weight. “This is considered severe duty,” Pettingill said. The trucks “use a high amount of fuel because they’re so heavily loaded, so it really puts the oils to the test.” 

The testing site was outside of the Toronto area in Ontario, Canada.

“Since you’re not used to seeing data from 0W-20 oils, for reference the field trial data includes data from an API-licensed FA-4 10W-30 oil,” Pettingill said. The 10W-30 oil was code named Test Oil Amber; Amber was the standard to which Test Oils Grey and Beige were compared. Test Oil Amber was mainly formulated with Group II base oil. 

The test methods chosen were common industry test methods often seen in used oil analysis reports, Pettingill said. Test methods included ASTM D445 for kinematic viscosity at 100˚C, ASTM D2896 for total base number, ASTM D664 for total acid number, ASTM E2412 for oxidation and ASTM D5185 for iron content. 

The results of testing were obtained via used oil analysis for duplicate runs of both test oils in similar trucks operating under similar duty cycles. 

At the conclusion of testing, the viscosity of Test Oil Beige strayed outside of SAE 20-grade limits into the SAE 30 region. Test Oil Grey maintained its intended viscosity throughout testing. “This would be indicative that Test Oil Grey would maintain its fuel economy better than Test Oil Beige because it did not thicken into the higher grade,” Pettingill said. 

Both Test Oil Beige and Test Oil Grey demonstrated improved total base number retention over Test Oil Amber, and the total acid number increase occurred at a higher rate for Test Oil Amber than for Test Oils Beige and Grey. 

“The good news for the 0W-20 products is that we don’t see any rapid base depletion and we don’t see any rapid acid increase,” Pettingill said. “It’s interesting to see this. Field trials often tell you things that you might not have expected. Probably one of the key enablers for these strong attributes is that these 0W-20 test oils are formulated with high-quality Group III base oils, which most likely enables an improved synergy between the additives and the base oils in these products.”

Test Oils Beige and Grey demonstrated good oxidation resistance, which is very important for oil integrity. “Lower oxidation is better,” Pettingill said. Test Oils Grey and Beige “are directionally better than Test Oil Amber. This is another good sign that these 0W-20 oils are holding out just fine. Resistance to oxidation means the oil is not thickening, so the oil maintains its integrity and the additive package continues to do its job.”

How well did Test Oils Beige and Grey maintain their resistance to wear? 

“Over time, any oil in an engine will show accumulation of wear metals,” Pettingill said. “They build up as the drain interval progresses. A very conservative industry limit for the amount of iron content would be 100 parts per million. Some OEMs say that’s more conservative than you need to be, and they would allow a higher limit on that.”

All three test oils maintained wear metals well below 100 ppm at the 50,000-kilometer point in the test run. However, Test Oil Grey was the standout performer, showing the least amount of iron metal accumulation. Of the three oils, Test Oil Beige demonstrated the highest level of metal accumulation. 

“The main thing is that we have demonstrated with our own field trials, under extreme, maximum loads, that solid engine protection is possible with a 0W-20 oil,” Pettingill said.  

Sydney Moore is managing editor of Lubes’n’Greases magazine. Contact her at Sydney@LubesnGreases.com