The Navistar DT engine family is a line of mid-range inline-6 diesel engines. With 
horsepower ratings ranging from 170 hp (130 kW) to 350 hp (260 kW), the Navistar DT engines are used primarily in medium-duty truck and bus applications such as school buses, although some versions have been developed for heavy-duty regional-haul and severe-service applications.
Prior to 1986, Navistar International, then known as International Harvester Company, used the DT engine in farm and construction equipment.
 From 1997 to 2004, the DT was also rebadged and sold by Detroit Diesel as the Series 40.
 The Navistar DT diesel engines are of a wet-sleeve design. This means that the cylinder wall (sleeve) is a separately machined part that fits into the cylinder bores cast into the engine block. The cylinder sleeve is in contact with the engine coolant, hence the "wet"-sleeve.
 Navistar claims that the wet-sleeve design enhances durability because the consistent wall thickness of the sleeve allows for consistent heat transfer, ensuring the cylinders stay round during thermal expansion. Additionally, they state that the hardened cylinder sleeve is more durable and wear resistant than a softer, cast-in wall. Also, the replaceable cylinder sleeves protect the block from damage (e.g. in case of foreign objects entering the cylinder) and can easily be replaced, which Navistar claims enables simpler restoration to original specifications. The wet-sleeve design also allows the engine to be rebuilt easily to factory specifications, sometimes without even removing the engine from the vehicle.
 This design is opposed to parent bore engines, where the cylinder walls are machined out of the bores cast into the block. International states that the uneven thickness of the cylinder walls causes the cylinders to become out of round during thermal expansion, increasing wear. Also, damage to the cylinder wall requires more extensive work to repair.
 From 1984 until late 1995, the DT engines used a Bosch pump-line-nozzle (PLN) mechanical direct fuel injection system. 1984 through 1992 DTs used a Bosch MW style pump, while the 1993-1995s used a Bosch P style pump, and starting what was called New Generation Diesel engine design, which is still the same basic block design. Mechanical injection was still utilized in trucks up into the 1997 year, but this is rare. In 1994, due to tightening emissions regulations, the engines were redesigned to use electronically controlled unit direct fuel injection. From 1994 to 2004, the engines used HEUI (Hydraulically actuated Electronically controlled Unit Injection) injectors, co-developed by Navistar and Caterpillar Inc. From 2004 to 2009, the engines use International's Electro-Hydraulic Generation Two (G2) unit injectors.
 From the time the United States Environmental Protection Agency's 2007 emissions regulations went into effect, the Navistar DT engines were available in three configurations in what turned out to be their final generation prior to discontinuation. These variants were renamed to conform to International's then-new MaxxForce engine brand.
 The engines were also available for defense applications under the MaxxForce D brand. The final generation MaxxForce DT was known as the MaxxForce D7.6I6, and the MaxxForce 10 was known as the MaxxForce D9.3I6. Modifications from the civilian versions included diamond-coated (metal nitride coating) injectors[citation needed] to enable the engines to run on JP-8 fuel.
 Other Variants:
 In 2004, the entire DT family of engines was updated to meet 2004 emissions standards set out by the United States Environmental Protection Agency. Changes to the engines included a new turbocharger (called 
EVRT, for "Electronic Variable Response Turbocharger") with movable turbo vanes to improve boost and reduce lag, a 
new, electronically controlled hydraulic unit fuel injection system, cooled Exhaust Gas Recirculation to reduce 
emissions, and new four-valve cylinder heads. 
 In 2007, the DT engines were updated once again to comply with stricter 2007 emissions standards. The DT 466, DT 570, and HT 570 
engines were renamed MaxxForce DT, MaxxForce 9, and MaxxForce 10, respectively. Among the new features were 
closed-crankcase ventilation and new wiring harnesses. The MaxxForce engines were first available in model year 2008 International trucks 
and IC Corporation school buses.
 In 2010 the DT engines were updated once again for compliance with 2010 emissions standards. They all received new, twin turbochargers, with higher-rated versions of the MaxxForce DT and all MaxxForce 9 and 10 engines receiving intercooling and aftercooling. Upgrades to fuel injectors, the EGR system, and cooling were also part of the 2010 modifications.
 2015 was the final production year for the MaxxForce DT. It was discontinued for 2015, with some buses being built as 2016 models. It continued in the RE for the 2016 model. It was announced on July 22, 2016, that the RE will be produced with the Cummins ISL9 and the DT offering was going away completely.