How Many Miles Can You Expect From The Average Semi-Truck Engine? Here's What Truckers Say

The engines used by the top semi-truck brands are built to last far longer than the average car engine. While most passenger vehicles start having major issues after 200,000 miles or less, a well-maintained semi-truck engine can last around 750,000 miles before requiring an overhaul. Some even push beyond that limit with proper care and quality parts. The longevity of a semi-truck engine depends on factors like routine engine maintenance, driving conditions, and engine type; basically anything that affects the durability and performance of any passenger car. 

Most semis have diesel engines, which are more durable and reliable than gas engines. Manufacturers such as Mack Trucks, Detroit Diesel, and Paccar produce engines that are known to cross the million-mile mark before needing a rebuild. Real-world experience backs up these numbers. Some Western Star and Kenworth rigs using these engines have been reported to reach 2 million miles or more on the odometer, according to accounts from truckers shared online. 

A semi-truck engine's lifecycle hinges on a number of important considerations other than routine maintenance. Operating conditions matter a lot, as highway use tends to be less demanding than stop-and-go urban traffic. Lengthy idling and short runs also wear down the engine, although newer diesels are built to minimize this. On the r/engines subreddit, u/Noisymime explained, "Oil pumps these days are designed to provide good pressure even at idle. On modern diesels, it will gunk up the emissions devices if you leave it too long (think hours rather than minutes), but older diesels are typically fine." Fuel quality is yet another significant consideration; cheap diesel will lead to carbon buildup and clogged injectors, resulting in early failure. Hauling heavy loads also regularly stresses engine components, which leads to faster breakdown. 

The engine model also makes a big difference, with the likes of the Cummins ISX, the Detroit Series 60, and the Paccar MX-13 commonly touted for ruggedness and a potential run past the million-mile mark. In a thread on the r/Truckers subreddit, u/makinbacon claimed, "I had a Volvo 2007 with a Cummins 450 ISX that I ran until 1.5 million with no overhaul." Many truckers opt for engine rebuilds rather than replacing the entire truck. A rebuild, which typically costs several thousand dollars, can add another 500,000 to 1,000,000 miles to an engine's lifespan. If properly maintained, a semi-truck engine can even outlast multiple cabs.

Experienced truckers emphasize that proper care is the key to getting the most miles out of a semi-truck engine. On a Quora thread, one owner-operator reported an amazing experience with their rig. "2008 Kenworth T660 Cummins ISX CM871 engine for 1.6 million," the unnamed commenter wrote. "Original transmission, original rear ends. I haul primarily light weight oversize freight."Another trucker, Richard Klaus, said his 2010 Freightliner powered by a Detroit DD-15 engine had logged over 1.2 million miles as of early 2022. "Still pulls well, peaks at 44 pounds of manifold pressure, and has 58 pounds of oil pressure. Thinking another couple years and about 1,500,000 miles before I even think about an overhaul." In both cases, drivers pointed to strict maintenance routines and quality parts as the reason their engines stayed reliable for so long.

Fleet trucks tend to have shorter lifespans because they are often run harder with less individualized attention. Owner-operators, who are responsible for their own maintenance, typically achieve longer-lasting engines. Some truckers even buy used rigs with over 500,000 miles and still squeeze out more before a rebuild. One user advised a regular rebuild schedule in a thread on r/Truckers. "Rebuild the top end at 750k and the whole motor at a million," they wrote. At the end of the day, the life expectancy of a semi-truck engine comes down to care and usage. With diligent maintenance, truckers regularly see their engines hit and exceed the million-mile milestone. Those who neglect upkeep, however, often find themselves facing expensive repairs well before reaching that point.