Oil analysis is a sure fire way to know what evil may lurk inside your engine. It can tell you if your engine is healthy or facing a serious problem. It’s also sometimes a way to extend changes.
Not changing worn-out or malfunctioning oil can cost you big time. And with engines and oils like they are today – and with new ones on the horizon – arbitrarily changing your oil as frequently as every 10,000 miles to 15,000 miles may mean you’re throwing a lot of money away if the oil is still working properly. So how do you know when it’s really time to change?
That’s what analysis is for.
But, even with analysis, check with the engine maker – or at least re-read the engine’s warranty – before you go long.
In spite of occasional setbacks, the emission standards imposed on truck diesels since the 1980s have lead to improved combustion, making the engines cleaner inside. Injection pressures have more than doubled in some engines since the mid-’80s, in many cases because of new hardware such as unit injectors and unit pumps. Fuel pumped in under 26,000-30,000 pounds of pressure, instead of only 14,000 as it used to be, mixes a lot better with the air in the combustion chamber. That’s one big reason why you don’t commonly see smoke coming out of exhaust pipes any more. Combustion chambers have also been modified in many engines to stir up the air more forcefully and swirl it into the sprays of fuel in the cylinder. Electronic controls advance the injection timing at idle and low load (it used to be retarded under those conditions).
All these factors cut down on unburned fuel and soot. So, even though there is still soot sneaking around the piston rings and into the oil (and recent changes to reduce nitrogen oxides as of October this year increase this) engines are still much cleaner inside. Less soot, unburnt fuel, and acids end up in the oil these days. The fact that trucks get better fuel economy also reduces what gets into the oil pan.
Greg Shank, staff engineer responsible for lube, filtration, and coolant technology at Mack Powertrain, cautiously allows that combustion has improved so much that, “while idling is still detrimental and we don’t encourage it, it’s not as big an issue as it once was.”
At the same time, engine oils, because of ever-tougher industry standards and an extremely competitive market, have been improved tremendously. Shank, referring to just one basic improvement, says “the engine manufacturers have driven the oil manufacturers to produce oils with a higher base number. So, oils are more acid-resistant than before.”
The latest change, the CI-4 API (American Petroleum Institute) standard, is the toughest ever, by a mile. It was created for post-September engines that will use cooled exhaust gas recirculation (EGR) to meet the 2002 standards for reduced NOx (nitrogen oxides). It’s designed to cope with extra soot and acids that will get into engine oil because of the exhaust gases in the cylinder.
Oil analysis is like a blood test. You take a tiny sample under conditions that ensure it’s typical of what is in the oil pan. This means running the engine till it’s hot and then removing the drain plug while holding a small bottle near the stream. You fill the bottle a few seconds after flow starts (to flush away concentrated ‘stuff’ that may be sitting on the bottom of the oil pan). This sample gets sent to a lab that measures everything you need to know about the oil.
Oil analysis helps you know when you really need to change your oil and filters. But it’s important to realize it can work both ways. Analysis sometimes says you need to change more often than you have been.
Charlie Flexter’s fleet, Char-Lynn Trucking in Dawson, Ill., hauls grain. He’s in a rural area but his vehicles sometimes do short urban runs. Flexter says analysis told him his engines were, at times, exceeding the oil’s ability to protect them, even with 15,000-mile changes. He tightened up the interval and saved himself some trouble and money.
Analysis will also frequently point out problems like coolant or fuel leaking into the oil through a seal failure that is often cheap to repair, yet can quickly lead to catastrophic damage because of oil dilution.
David Nycz, fluids analysis data consultant at Caterpillar, says, “At Cat we use the word ‘optimize’ instead of ‘extended’ when we refer to customized drain programs. In some severe applications, oil analysis may indicate that the standard oil drain is the maximum or even that a shorter drain is desirable.”
So, analysis is even better insurance than frequent changes.
Mack’s EGR engine will feature two more quarts in the oil pan and an improved centrifugal filter just to keep its oil change interval from being shortened. The new EGR engines will need the new CI-4 oil, and will need careful testing before lengthening change intervals past the standard recommendation.
What it measures
“Oil analysis consists of a series of laboratory tests conducted on the engine lubricant,” says Detroit Diesel’s performance products development manager. “Most tests indicate the condition of the engine, while some reveal the condition of the lubricant.”
One important test measures the oil’s viscosity. You probably know this property refers to how thick the oil is. Oil gets thicker as it becomes loaded up with soot or when high temperatures make it oxidize. Oil that’s too thick won’t circulate properly and engine parts start to suffer from inadequate lubrication. Oil can also thin out if it has been exposed to extreme heat or if there are leaks of raw fuel or coolant into the engine. Thinning can also happen if any bad injectors fail to atomize the fuel properly or if there’s a lot of idling in cold weather. Thin oil won’t produce a thick enough oil film on engine parts to protect them from wear. Analysis will show whether or not the viscosity of a batch of oil has changed up or down one viscosity grade, meaning it’s time for replacement (some engine manufacturers recommend you dump the oil after a specified, small percentage change in viscosity). The analysis will even tell you just why the oil has gotten thick or thin.
Another oil property a good lab measures is Total Base Number. TBN is important because combustion produces acids that get into the oil. TBN measures the level of an alkaline oil additive that neutralizes those acids, just like Alka Seltzer or Tums neutralize stomach acid. The TBN tells you how much of the additive is left, or, if the material has run out and the oil is acidic. The lab will also tell you just how acidic it has become with a TAN (Total Acid Number).
The second basic type of information a good oil analysis contains is wear metals. Measuring the concentration of various metals and comparing it to the mileage since the oil was changed will tell you exactly how fast engine parts are wearing. A good lab report includes total concentrations of metals such as iron, chromium, nickel, lead, aluminum, copper, and tin. Each comes from different parts of the engine. Knowing the concentrations of wear metals becomes a critical tool in determining the change interval.
Choosing a lab
Not all laboratories give the same high quality oil analysis. Greg Shank says, “You get what you pay for. I don’t recommend the $3 to $5 analysis. A good price range is $12 to $18.”
He recommends, in addition to viscosity, wear metals, TBN and TAN, that you get a report that contains a separate measurement of soot level (which may be called either TGA or LEM.) “You need to know the percentage of soot in the oil,” he says. Eric Thompson, director of heavy-duty service engineering at Cummins, Inc, says the lab should also be able to measure how much oxidation has occurred because this will cause poor oil pumping during cold starts. Yet, many labs don’t measure it accurately.
Shank and Hart both said a lab should be asking in detail about the year and model of your engine. Without knowing what an engine is made of, there’s no way they can draw meaningful conclusions about what the levels of wear metals mean.
The Technology and Maintenance Council’s Recommended Practice on Used Engine Oil Analysis points out that the lab must verbally interpret the results for you rather than just send you a bunch of numbers that won’t mean much to you. Cat’s David Nycz says, “The most important part of Caterpillar’s S.O.S oil analysis, offered through Caterpillar dealers, is the interpretation of test results.” TMC adds that the lab needs to have a way to alert you immediately if they pick up a serious engine problem so that you can fix it.
Hart recommends a lab like the one that supplies Detroit Diesel’s POWER Trac analysis. This facility has ISO 9000 quality certification, and uses a digital spectrometer to measure 21 of those wear metals. Nycz says that your analysis results should include information not only on oxidation, but also on contamination from fuel, coolant, and water (a byproduct of combustion).
You must first establish normal wear patterns by following conservative change intervals and having an oil sample analyzed at frequent, regular intervals (say every 2,000 miles) near the end of that interval. When oil is doing its job, the concentrations of wear metals increase right with the miles, so that at 20,000 miles you’ll have exactly twice as much metal as at 10,000. When the oil quits working with full effectiveness, the concentrations will build up more quickly. You might then see iron doubling in 8,000 miles instead of 10,000 miles. The lab also needs to evaluate the content and character of the oil to make sure you won’t end up with piston deposits, a problem that often sends a diesel in for overhaul. All this lets you and the lab determine the point at which the oil’s useful life ends so you can change it just before that happens.
You need to maintain any warranty coverage or potential good will protection you may have by getting factory approval before instituting an extended change interval. This is worthwhile because it ensures that experts have seen that you’re doing everything right. In some cases, large oil suppliers will warrant your engine against an oil-related failure and cover you.
Here’s what each engine manufacturer had to say about approving extended changes:
David Nycz says, “A customer can maintain the factory warranty when utilizing an optimized oil drain program.” He goes on to say that Cat will warrant an improperly manufactured part or improperly assembled engine, but not a failure resulting from an over-extended oil drain. “If an oil company guarantees the performance of their oil in extended drain applications, then the oil company is responsible for oil related failures.”
Oil analysis alone “should not be used to extend oil drain intervals,” says Ed Hart. Detroit Diesel will approve extended drain intervals when certain criteria are agreed upon in advance between the customer and Detroit Diesel engineering. These criteria relate to consistent changes at the scheduled mileage, consistent additions of make-up oil (to keep additives replenished), a favorable duty cycle, and use of quality oil and filters.
Eric Thompson says Cummins has already lengthened change intervals to just about the practical maximum in a desire to help their customers reduce costs. “We’re not as conservative as we were in 1991. Today, an ISX that gets over 6.5 mpg has a recommended change interval of 45,000 miles.”
“Oil analysis is a good way of catching potential failures before they become big problems.” Thus, Cummins sees analysis more as a way to protect yourself from engine trouble than to further extend changes. Cummins people have also experienced a lot of “variability” in the quality and consistency of lab test results. Thus, they recommend the use of the Fleetguard Monitor fluid analysis offered through their distributors, or at least consulting your distributor to find a good lab. If you should try to use analysis to take your change intervals out to the limit, work with your Cummins distributor to help ensure you’re protecting yourself.
Greg Shank says, “We encourage the use of analysis. It can be used to extend changes if done scientifically.” A critical factor is the “duty cycle” of the engine-i.e. engines that get good fuel mileage and see little idling are better candidates for extended changes.
Greg Holderfield, director technical support, says, “Yes, an oil analysis program is recommended. Any extended drain intervals would definitely require an analysis program. However, Volvo Trucks of North America does not endorse any kind of extended intervals beyond our published drain intervals.”
Caterpillar also provides its own premium branded oil and filters. Plenty of filters adequate for extended changes are available in the aftermarket, but you need to assure quality. Filters that aren’t designed to live long enough for extended changes can leak or bypass before you change.
Note that four items are critical to the success of an extended drain program:
- Use premium oil and filters. “Don’t treat oil and filters like a commodity,” says Mack’s Shank. “The customer has to be willing to pay a little more.” Factory filters are normally of premium quality, but higher priced filters in the aftermarket are often in the same category. Make sure the filter supplier guarantees that the filter has the capacity and durability necessary for the change interval you adopt. Cummins’ Thompson says premium filters often have media and seals that will survive long enough to last through an extended interval while lower grade filters do not.
- Change consistently right near the correct interval-no missed or greatly delayed changes.
- Refill the oil pan daily. This will ensure a constant re-supply of critical oil additives.
- The truck needs to operate in a favorable duty cycle typical of highway cruising where it gets good fuel economy and sees little idling.
Doing all this may allow many truckers to safely extend oil changes. A properly monitored extended drain program will save dollars on oil, filter, downtime, labor, and disposal costs, while helping them catch many small engine problems before they develop into major ones.
“However,” says Caterpillar’s Nycz, “you must consider this: the savings from extended oil drains are relatively small compared to the overall cost of fuel and maintenance, and certainly not high enough to make it worthwhile to put an engine at risk. On the other hand, an engine with a complete analysis history is worth more at trade-in.”
Choosing a lab
Many of the large, national engine oil manufacturers offer oil analysis combined with technical advice as an integral part of the marketing program for their premium engine oils. Premium oils are usually formulated with the goal of protecting your engine while also making extended intervals practical. By using their oil, combined with the services, you end up being able to optimize your change interval safely. You may also get the analysis service free or at low cost, and it comes with technical advice. When you add it all up, the total cost of lubricating your engine usually ends up being lower because the higher cost of a premium oil is more than offset by the savings associated with the longer change interval.
You may want to shop around on the websites of the oil manufacturers we’ve listed in this article. Go to the web address, and then click on an appropriate link like “products and services,” or type “oil analysis” into the site’s search engine.
For more information, contact:
Exxon Mobil Corp.
(800) 443 9966
Mobil Delvac Accutrack
(Click on Chevron or
Shell Oil Products U.S.
Pennzoil-Quaker State Co.
Citgo Petroleum Corp.
Cummins Engine Corp.
Volvo Trucks North America