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Is your oil “swelling?”
Recently, I was contacted by a reader who thought his oil might be “swelling,” because he got dipstick readings above the full mark immediately before changing oil. He wanted to know if oil could possibly “swell.” Many modern low oil-consumption diesels could easily give the operator the impression that oil was swelling in service.
The reader was told that diesels with high EGR rates collected so much soot in the oil that it caused significant expansion. During a typical oil change interval, the oil in the sump may collect as much as 4% to 5% soot, primarily in P&D service. However, soot particles in modern oils are very small (less than one micron), so they don’t add significant volume to the crankcase oil. The slight increase in volume would be very difficult to read on a dipstick.
The major reason for crankcase oil to “swell” or expand in service is fuel dilution. Diesel fuel is much more critical than gasoline in this regard. A fully warmed-up gasoline crankcase will reach temperatures as high as 300 degrees F, and gasoline oils are much thinner (typically SAE 5W-20 grade) than diesel oils. Gasoline (and low viscosity oils) are mixtures of many compounds from relatively heavy compounds to very light compounds (called light ends) to assist in starting a cold engine. Subsequently, hot automotive crankcases evaporate many of the lighter ends in gasoline engine oils. This prevents swelling, and it is why there is a NOACK volatility specification for modern passenger car oils.
Diesel fuel is significantly less volatile than gasoline since the range of compounds in diesel fuels tends to be much narrower with few “light ends.” In addition, fully warmed-up diesel engine crankcases operate at much lower temperatures. The majority of diesel oils tend to be SAE 15W-40 viscosity grade, which is thicker, therefore less volatile, than gasoline engine oils. As a result, very little of the diesel fuel in the crankcase is ever driven off (evaporated), and fuel dilution can easily be observed when checking with a dipstick. It is possible to observe diesel fuel dilution levels as high as 7% to 10% in P&D operation.
Coolant dilution also can cause an apparent increase in the quantity of oil in the crankcase, but most of today’s diesels have addressed that problem with improved cylinder liner sealing. If you should see coolant in the oil when you are changing it, and it is pretty obvious, oil expansion is perhaps the least of your problems. Get your engine into the shop quickly!
But the reader’s question made me think about some of the other things that could give vehicle operators the impression they are “making oil” in the crankcase. For example, you should always check the oil on level ground. Dipsticks are supposed to be placed in the middle of the crankcase, but vehicles setting at different angles have different amounts of oil d...
Optimizing Oil Drains
While some fleets strictly adhere to manufacturers’ recommended drain cycles, other fleet managers use various techniques to extend the interval between oil changes. This month, FE examines what savvy fleet managers should consider before “going long” on engine lubrication.
Fleets may save money by extending oil drain intervals, but how far is too far? What can be done safely that won’t jeopardize the engine?
On one side is the understandable and generally cautious position of engine OEMs and the oil manufacturers who don’t want to encourage practices that may jeopardize engine performance. On the other side are the economic and environmental pressures that are forcing fleet managers to look harder to find more dollars. It comes down to what is reasonable that still supports manufacturers’ recommendations. “As fleets, we have to make sure we are using everything to our advantage to keep our costs in line,” says Darry Stuart, president and CEO of DWS Fleet Management Services. “And we always pick on drain intervals.
“I don’t like the term ‘extending’ oil drains,” says Stuart. “I think ‘optimizing’ is a much better word” for the process and reasoning that he describes to justify adding miles to the interval.
There are many quality oils from which to choose, and the choice of oil may not be the determining factor in setting the interval. According to Stuart, “The most important thing about optimizing oil drain intervals is to make sure you have a PM [preventive maintenance] program that supports whatever interval you choose to use.” One of the key points to a quality PM,” he adds, “is to be consistent” and to audit the PM process to make sure that your people are performing the tasks and doing them the same way each time. Those items should be familiar: checking tire air pressure, load-testing batteries, pressurizing the coolant system, torquing wheel nuts and U-bolts, and greasing and lubricating the vehicle. “If those procedures are correct, then you can optimize your drain intervals,” Stuart says.
For the engine specifically, he recommends checking belts, idlers, tensioning, air restriction in the air filter, “and make sure you get maximum life out of your air filter.” Stuart points out that recently there has been some concern about fuel filter life and the quality of ultra low sulfur diesel (ULSD) fuel. “We are probably getting to a point where we’re going to have to increase our ability to filter the fuel in order to get to maximum oil drain intervals.” He notes that fuel filter life has been cut in half in some instances, for reasons not fully understood now. Stuart thinks the industry should consider additional filtration. He believes the capacity is available in oil and fuel, and “we could get to the ...