Today’s truck engines have parts that fit better, expand and contract less, and have smoother surfaces than ever before, so you might think breaking in is much less important than it used to be. But no engine starts out perfect – there are still tiny irregularities in the surfaces that break-in helps smooth over.
A remarkable thing happens during those first miles of running a truck engine. The very same soot that is always thickening your oil, eventually making it gritty and abrasive, actually does you a favor. The fine carbon particles that naturally get into the oil form an abrasive polishing compound. The breaking-in is a lot like sharpening a knife on a stone covered with oil.
“During break-in the engine is going through an initial wear cycle,” says Ken Nolte, a Caterpillar test and demonstration driver. “At different stages in the life of the engine it will wear at different rates. During this period, all of the new parts are settling into the normal operating clearances that it will have for most of its life.”
There is always a potential for problems with any engine or truck, Nolte says. Following appropriate and recommended maintenance procedures and using good driving practices are of vast importance, particularly at the time of break-in. “Start it out right and take care of it and it will work for you,” he says.
The first break-in
These days, engine manufacturers make a major effort to break in their engines before they’re ever put into a truck.
“Cummins’ cylinder kit technology enables us to produce a fully broken-in engine before it leaves the Cummins manufacturing plant,” says Zack Ellison, director of customer technical support at Cummins. “Cummins tests and verifies each heavy-duty engine at full power before it leaves the plant.”
Mack’s Dave McKenna, power-train products marketing manager, concurs. Thus, he says, most engines have “been through several heat cycles of operation,” a large part of the break-in process.
The latest manufacturing techniques also make for more precision when machining parts. “We now know how fast and how much different types of metals expand or contract during the normal operation of the engine,” says Caterpillar’s Nolte. “Because we know this, we build the engines to be as close to normal operating specs as possible when they come out of the factory. That means less break-in time for the driver.”
Meanwhile, changes in materials for engine components improve durability and reduce oil consumption. “Some examples of these changes include Monotherms, one-piece pistons with better piston-to-liner clearance for better oil control and less blowby; induction-hardened liners; and improved piston ring materials,” Ellison says. Likewise, cylinder liners have a smoother finish. “This results in a better sealing process for lowered oil consumption resulting in no need for break-in.”
Driving your new engine
Yesteryear’s instruction books typically included a paragraph advising the driver to baby a new engine a little. They recommended avoiding prolonged periods of full-load, peak-rpm operation and ensuring the engine was exposed to a wide variety of operating conditions.
Today, most engine manufacturers are so confident in their fresh-from-the-plant engines that they have no special driving recommendations at all.
“For the driver of a new Cummins heavy-duty engine, Cummins’ recommendation is to just drive it,” Ellison says. “There are no special instructions for rpm, loads, etc. for any initial mileage or set amount of time.”
Volvo’s Jim McNamara, manager of media relations, likewise reported the company’s policy on break-in to be nonexistent. “Volvo does not have any recommendations regarding break-in periods for Volvo engines,” he says.
Earl Evans, who runs a one-truck operation hauling both air freight and general freight out of Canfield, Ohio, says his dealer gave him no special instructions as to breaking in his Caterpillar C15. With a new engine, he says, he does “look under the truck and watch things, but I never had any issues. Also, the oil consumption was hardly any different when it was brand-new.”
Still, during those first few miles, it’s especially important to do the things you should be doing throughout your engine’s life.
“The practices to follow and the things to avoid are the same techniques that should be used throughout the engine’s life, not just during ‘break-in’ time,” says Caterpillar’s Nolte. “The things to avoid are extended idling, cruising at high speeds, not using progressive shifting, and similar bad practices. Extended idling has always been hard on your engines.” All three practices waste fuel, too.
“As far as watching the gauges,” Nolte adds, “good driving practices will keep the driver monitoring the lights and gauges at all times.”
“We ask the driver to limit maximum throttle operation until the coolant gauge starts to move,” says Chuck Blake, Detroit Diesel’s manager of customer fuel consumption analysis, “which is good advice for any engine at any mileage.” Under-hood inspection should be an everyday practice, he says, to catch minor problems. Check the oil on a level surface, and don’t overfill or run low.
Maintaining your new engine New-engine maintenance is almost identical to broken-in engine maintenance, our sources report.
Caterpillar’s Nolte says a cooling system sample should be taken at 500 hours. “This is done to establish a baseline for the engine and to also check for any problems. The fluid levels should all be checked daily, more often if there is a problem suspected.”
For ’07-compliant engines, use an API CJ-4 rated oil, Nolte adds. The recommended change interval in most trucks is 30,000 miles or 500 hours. “At that time a service would include oil and oil filter change, fuel filter change and a few other checks to be performed,” he says.
Cummins’ Ellison concurs. “CJ-4 oil is the standard for Cummins heavy-duty engines. Drivers should always refer to the Cummins Owner’s Manual for recommended maintenance practices and intervals.” There is no special interval for break-in.
But one special procedure on all new engines, except those made by Cummins, bears careful attention. The “overheads,” or valve and injector mechanisms, on diesel engines are set periodically. For the valves, it’s a matter of loosening up the adjustment and sliding a feeler gauge between the rocker and the valve itself or a bridge that operates two valves. For injectors, it’s typically a matter of adjusting the rocker to the injector’s height, using a special tool provided by the factory or a high-quality aftermarket tool maker. This keeps the injector operating on the proper part of the cam so it pumps at the proper rate throughout each injection cycle.
Making these adjustments is a complex procedure and requires skillfully turning the engine over with a breaker bar and putting the crankshaft at exactly the right position to adjust each valve and injector, according to a precise pattern and sequence established by the factory. Even experienced owner-operator mechanics like Gordon Bow of Oakfield, N.Y., a man who has actually lengthened his own aluminum trailers, normally leave this procedure to experienced technicians. Bow had his Series 60 overheads done initially according to Detroit Diesel recommendations.
In general, the overheads wear a little differently and the initial settings change more during the break-in period, often necessitating making an early overhead adjustment. One factor here is the pounding that valves take as they hit the cylinder head each time they close. They often rise a little in the head during break-in, making the lash adjustment too tight. Once the engine is broken in, and the adjustments are reset, the settings become much more stable. Setting the valve clearances and injector height at the initial interval will go a long way toward guaranteeing long life for the valves and the valve and injector actuating parts, as well as keeping injectors operating at full performance. (On pre-electronic engines, injector settings can also affect injection timing, but that is not true of today’s engines.)
Here are the overhead adjustment recommendations by engine manufacturer:
Caterpillar: “The initial adjustment of the overhead should occur between 15,000 and 60,000 miles,” Nolte says. “After that it is scheduled at 300,000 miles or 6,000 hours under normal conditions. The initial service is very important. At that time the engine would be thoroughly checked and adjusted to achieve the best performance possible.”
Detroit: “60,000 miles is the number initially stated,” Blake says of the valve adjustment. “Remember, no injector lash, just the valves. This early look should catch any break-in wear or problems with settings during assembly.” After that, the nominal 60,000-mile interval actually remains the same but is far less critical. The company suggests discussing your operational pattern with the distributor and getting their advice on when to do additional settings. On Detroit Diesels, the injector height is set at the first sign of deteriorated performance, but it normally changes very little.
Mack: “The Mack MP7 and MP8 engines have identical valve adjustments, which are 125,000 miles or 12 months for the initial adjustment and every 250,000 miles or 24 months after that,” McKenna says.
Volvo: The owner’s manual states that the intervals are the same as with Mack.
Cummins: “There is no initial setting requirement for Cummins heavy-duty engines,” Ellison says. “Cummins recommends setting overhead every 120,000 miles for ISM engines and every 500,000 miles for ISX engines. The Cummins ISX unique design includes fewer wear joints, resulting in the recommended interval of only every 500,000 miles.”
Most specifications state an acceptable range for the valve clearances, which means you often don’t need to reset them, just check that they are still acceptable. Earl Evans loosens every adjustment and resets each on his Cat C15 so the right gauge just slides perfectly, which is the ideal adjustment. He did the initial setting at 60,000 miles and continues at 100,000 miles “because they deserve it for what they go through,” he says.
Break-in and MPG
Many owner-operators have experienced a noticeable improvement in fuel economy as their engines wore in. Earl Evans was hauling very light, air-freight loads on level roads for the first 100,000 miles he drove his C15. He was at first disappointed by how tight the engine was – and by the fuel economy. Fortunately, he got back into long-haul, heavy freight with long climbs involved. As soon as this happened, the engine seemed to run better, and within 25,000 miles it was much looser and giving good fuel economy. Owner-operator Gordon Bow says his Series 60 seemed to take about 60,000 miles to loosen up so it ran at its best.
“The engine should begin to achieve its best mileage and performance after about 40,000 to 60,000 miles,” says Caterpillar’s Ken Nolte. “This would occur after the overhead has been checked and serviced as needed. It is possible that the driver would notice a measurable change in both at about that time.” Mack’s Dave McKenna agrees with the 40,000-mile lower threshold for improved fuel economy.
Sometimes when an operator notices improving fuel economy as the truck is broken in, it’s not just the engine, points out Cummins’ Zack Ellison. “A Cummins engine is optimized for fuel economy when it is built,” he says. “There are, however, a number of components on the vehicle that may impact optimum fuel efficiency. Tire tread is an example of a vehicle component that will change over time. As the tire tread wears in, fuel efficiency will improve.”
Detroit Diesel’s Admir Kreso, manager of HDEP performance, says, “Interestingly, the other systems on the truck have a break-in period, too. These include the transmission, braking systems and even the aftertreatment.”
Chuck Blake of Detroit Diesel agrees that break-in incorporates many factors and not just the engine. “The number of miles taken for engine break-in is a factor of load and engine speed operation,” he says. “The truck, the engine and the tires break in at different rates. Fifteen-to-twenty-five thousand miles is probably a good range for the engine. Max fuel efficiency is affected by weather, so mileage alone won’t suggest max mpg.”
Mike Powers, Caterpillar’s on-highway product development manager, says the company has noticed that its ACERT engines take a little longer to fully break in than earlier designs, about 60,000 miles rather than 40,000. This suggests that Caterpillar’s unusual air handling technology (twin turbos and variable intake valve timing) and other aspects of ACERT may well reduce the tendency for carbon soot to form in combustion and find its way past the piston rings and into the oil.
For more information:
Caterpillar Engine Div.
Detroit Diesel Corp.
Mack Trucks, Inc.
Volvo Trucks of North America