When you check the level in your crankcase, you’ll find the level higher if using CJ-4. That means money saved on make-up oil.
The 2007 emissions standard will bring big changes for truckers. Change can be scary, but the research that makes engines cleaner always does more than just clean the exhaust. It also improves the technology.
These changes bring a lot of good news, especially for those running pre-2007 vehicles. The biggest part of that good news is CJ-4 diesel engine oil, which is so much better than the CI-4 it replaces that it will be well worth the higher cost. CJ-4 is a lot better in the ways it performs in almost all areas, and it needs to pass much tougher tests to prove what it can do.
To decide whether or not you should switch from CI-4 to CJ-4, you need to understand that the fuel, the engine and the oil work together as a system. Once you see how they cooperate, the decision should be easy.
What oil fights
The biggest challenges for oil are heat and the soot, acids and sludge or deposits that form when fuel burns imperfectly. Although the particulate level drops in 2007 to 1/10th what was allowed before, this is not much of a challenge for the engine. A Diesel Particulate Filter or “DPF” (see July Big Rig Basics) will be collecting the soot outside the engine with very little effect on the operation of the engine itself.
The larger challenge for the oil is the 40 percent reduction in NOx or nitrogen-oxides, which is also required. NOx forms when the burning gases in the cylinder get too hot. Most truck makers have been recirculating some of the exhaust since 2002 to reduce the NOx. Exhaust soaks up a lot of heat, reduces the temperature in the cylinder and lowers the NOx.
The 40 percent reduction in NOx will be met with familiar systems – EGR (exhaust gas recirculation) and Caterpillar’s ACERT, with Cat adding a slightly different form of EGR called Clean Gas Induction.
It was having more exhaust from EGR going through most engines that worried engine oil makers and motivated them to develop the CJ-4 grade. What worried them most was additional heat and pressure, especially the heat. When an engine needs to recycle more exhaust, both the heat and pressure in the cylinder are likely to increase. The heat goes up because the exhaust is warm – nearly 300 degrees F. – and there will be more of it. The pressure goes up because there’s more total stuff going in – the same amount of air plus the additional exhaust.
Heat attacks the oil mostly where it sits between the piston and cylinder liner when lubricating those parts. It also reaches the oil where it flows inside the top of the piston, right under the crown, to cool it. Too much heat can have a very destructive effect on engine oil.
An additional worry was soot in the oil. Having a lot of exhaust in the cylinder often results in more soot getting around the piston, onto the cylinder liner and into the oil, though no more soot may come out the exhaust pipe.
Where CJ-4 is better
The oil makers went to work and developed new and better super-oils to combat the additional stresses.
“To meet the enhanced performance requirements of the 2007 engines, the CJ-4 oil is designed for better oxidation stability, high soot dispersion capability, better piston deposit control, increased wear performance and reduced oil consumption,” says Reginald Dias, director, commercial products, ConocoPhillips Lubricants.
Oxidation stability means the oil won’t combine with the oxygen in the crankcase, thicken and form acids that can eat away at bearings. Oxidation stability is harder to maintain when the oil is subjected to more heat.
Soot dispersion means soot remains dissolved in the oil, so it’s no thicker or grittier than when it is new. Reduced oil consumption saves truckers money because they then have to add less. But it’s also critical when running a truck with a DPF.
“The new oil is more robust and is capable of handling the higher engine operating temperatures and higher soot from heavy EGR,” says Citgo Petroleum Corp.’s heavy-duty lubricants manager, Mark Betner.
Chevron’s Jim McGeehan, global manager of diesel engine oil technology, headed the American Society of Testing and Materials committee that developed the tests. He mentioned the Mack T-12 test, which “involves high EGR rates, double the 2002 levels,” and the fact that the oil in the sump is held at 260 degrees F., much hotter than it normally runs. The new oil must protect critical engine parts even under those conditions.
That is a very difficult test to pass because heat thins the oil out in two ways. Just being hot makes it thin, so it loses viscosity – that thick quality that keeps metal parts from rubbing together. And if oil stays hot for a long time, it changes chemically – like cooking an egg – and gets even thinner. Passing this test shows that the oil retained its viscosity and protected the parts even under conditions most engines will never see.
Another test, the ISB test, runs the engine until the soot in the oil reaches 6.5 percent of what’s in the crankcase, a very high level, McGeehan says. It then looks at some critical parts, like the injector screw, that the oil has a tough time protecting even under good conditions.
Detergents keep soot in the oil dissolved, but if they don’t work well enough, several nasty things happen. First, the oil will thicken, preventing proper pumping and circulation through the engine. This deprives some of the parts of oil and becomes more of a problem when the engine is started cold because it takes too long for the oil to get to the parts.
The soot can also form a damaging abrasive like sandpaper when it is no longer dissolved. If an oil fails this test, the engineers see actual scratches on the surfaces of the parts. An oil won’t pass this test until the wearing parts look good.
The third problem is that, since soot forms solid grit in the oil, it often clogs filters. But soot that’s dissolved just goes right through them. The ISB test checks for filter clogging, too.
The ISB test even checks for deposits inside the cam cover, a place where they can form very easily. Deposit control is so important because most diesel engines that are cared for never wear out. Deposits on the piston rings make them stick, the engine starts to use oil, and the user then overhauls the engine because of the cost of adding oil. Deposits and related oil consumption will be even more of a problem for trucks running DPFs because that will mean more frequent cleaning.
In connection with deposits, McGeehan also described the Caterpillar C13 ACERT test. It runs the engine for 500 hours straight at full load and then looks at piston deposits and oil consumption. While ACERT exposes the oil to less heat and soot, piston deposits can be an issue because the fuel takes just a little longer to finish burning with ACERT, and that can leave a trace of gunk on the piston. Since the parts must look clean after the test and oil consumption does not increase, it’s clear all CJ-4 oils will control deposits much better than earlier oils.
In interviews with experts from BP and Castrol, ExxonMobil and Shell, deposit control and wear protection improvements were mentioned consistently. McGeehan later mentioned “verified longer wear in the field” for the new oil grade. Shell has publicized results showing 38 percent reduction in wear and even 50 percent or more on some parts. They are even planning to phase out CI-4 in all but bulk sales.
All the other oil companies make generally similar claims, and Citgo’s Betner says, “I would prefer CJ-4 even in a 2004 truck.”
As if this were not enough good news, the engine makers have made some improvements in their 2007 engines to combat the anticipated extra stress. All have improved their injection systems to do a better job of mixing the fuel and air. This means less air going in than before, so the pressure in the cylinders goes up much less than expected. EGR coolers have been improved too, and this means less heat. Cummins, for example, claims no increase in either heat or pressure. Many engines have been increased in size or beefed up or both.
What this means is that the oil is probably better than what is actually needed, even for the 2007 engines – quality overkill. The result is likely to be longer engine life and fewer repairs for those willing to pay a little more for oil.
Where CJ-4 is not better
There is just one area where CJ-4 is not an improved lubricant. Oil has a quality called TBN or Total Base Number. TBN is exactly like Alka Seltzer or any other antacid for your stomach. As a diesel runs, acid forms in the crankcase, and it will attack many of the parts, especially the bearings, making them soft and subject to abnormal wear. But if it’s neutralized with a chemical, it becomes harmless. This is what TBN additives do.
The quality of TBN, and also their ability to keep engine parts clean, called “detergency,” is produced by fancy additives that most of the time contain something called “ash.” Ash in small amounts won’t hurt an engine, but it’s not good for the DPF. The problem is that the DPF is so good at what it does that it sorts out and grabs not only the soot, but the ash that’s in the exhaust. This is the tiny bit of ash that comes through from the oil the engine consumes.
Heat produced under load, or via a tiny bit of extra fuel in low-load conditions, will make the soot burn off as fast as it is collected. But no amount of heat can burn the ash. So eventually (after 150,000-200,000 miles or more in over-the-road trucks), the ash will build up to the point where the DPF begins to clog. The driver will see an indicator light on the dash telling him to have the DPF cleaned.
To meet the EPA’s minimum standard of 150,000 miles for the cleaning interval, the oil refiners reduced the amount of ash in the oil. This means that the level of TBN protection may be just slightly less than before.
But before you get worried, realize that the engine, fuel and oil are a system. Most of the diesel fuel on the market is already ultra low sulfur diesel. Better refining has reduced the sulfur level all the way from 500 ppm (parts per million) down to 15 (33 times less) because sulfur interferes with DPF operation and produces particulate.
Fortunately, most of the acid in engine oil comes from the sulfur in the fuel burning to form sulfuric acid. Bottom line: For anyone running ULSD, the oil needs much less TBN than before to protect the engine. The lower TBN in CJ-4 is no problem.
Of course, 20 percent of the fuel produced for highway trucks, except in California, is still low sulfur diesel, with the old, higher levels of sulfur. Ideally, you would run a combination of ULSD and CJ-4 in any truck to see the best results.
But what do you do if you have a good source of LSD, are running a pre-2007 vehicle and want to use the earlier fuel to save fuel dollars? No problem here, either. For one thing, CJ-4 oils are licensed to replace CI-4 – to be backward compatible. Several of the tests they must pass are run with the engine using LSD. The TBN protection is only slightly lower and will normally be more than sufficient.
Also, the situation is eased by the fact that not all the acid in the oil comes from the fuel. Some of it comes from the oil itself, as it is exposed to heat and the air in the crankcase over long miles.
Here again, the higher quality of the oil helps. CJ-4 needs to have greater oxygen stability, and that actually reduces the acidity. In other words, even if running LSD with CJ-4, you’ll still need a little less TBN than before. Alex Buhlkovsky, an engineer with ExxonMobil, says their oil is so much better refined and forms so much less acid over long miles on the road that even with a lower level of additive, the TBN actually lasts longer. Steve Goodier of BP says they have opted for an exotic form of additive that produces TBN without ash, so their best CJ-4 has a TBN rating equal to their earlier oils.
Jim McGeehan provided the simple answer as to how to handle this issue. If running only LSD and using CJ-4, seek the advice of your engine manufacturer. They will tell you if you should shorten your change interval slightly. You might be spending a little more on oil changes, but you’ll be reducing engine wear.
Can I use CI-4 with a DPF?
Some small fleets may have several pre-2007 vehicles and only one or two 2007 trucks. They may want to use just one oil and save money by continuing with CI-4. Some engine manufacturers may approve this because, with most DPFs, the only effect will be that it will have to be cleaned more often to remove the additional ash. Just make sure to get engine company approval because some DPFs and some engine systems may not work well on LSD.
On the other hand, the smart thing probably still would be to switch to CJ-4. Why? Because the amount of ash that gets into the DPF, and the frequency of the cleanings, is not only determined by the amount of ash in the oil, but by the amount of oil the engine uses. CJ-4 reduces deposits and wear, along with being more resistant to oil consumption, and that means much less oil and ash getting past the rings, and fewer cleanings, over the life of the engine.
Since you’ll be reducing not only maintenance on the DPF, but maintenance and overhaul costs on all your engines, you’d probably be smart to spend a few extra dollars and use CJ-4.
For More Information:
ExxonMobil Lubricants and Specialties
Shell Oil Co.
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