The Navistar International 7.3L V8 diesel turbocharged T444E engine was modeled off the base of the 7.3L Ford PowerStroke engine that powered Ford Super Duty 250/350 trucks. The International T444E engine is found in both mid-size and full-size school bus models from 1994 – 2004.
This 7.3L T444E diesel engine guide is a part of our Diesel Engine Guide series to help with buying a school bus for sale.
This article will dive further into the T444E engine including:
- Engine Overview
- Engine Specs
- Towing Capacity
- Life Expectancy
- Maintenance Requirements
- Typically paired transmissions
- Common engine problems
- Engine comparisons to the 5.9L Cummins, DT466, and more.
T444E Engine Overview
Navistar International produced its 7.3L V8 diesel turbocharged engine series from 1994 to 2004 for use in school buses, and Ford trucks and vans.
During manufacturing, it was one of the largest mass-produced diesel engines. The company produced more than 2 million of the engines for Ford at its foundry operations in Indianapolis, Indiana, which closed in 2015.
The engine, known as the T444E or PowerStroke, is best known for powering Ford Super Duty 250/350 diesel trucks, Ford Excursion sport utility vehicles, and E-series vans. The engine also was part of the bus chassis for Navistar International Type C school buses and other large commercial vehicles.
The T444E engine name derives from its featured turbocharger (T) and electronically controlled components (E).
At approximately 930 pounds in weight, the T444E is lighter than other commercial vehicle diesel engines produced by Navistar International and Cummins.
T444E vs 7.3 PowerStroke
The T444E and PowerStroke are basically the same engines except for a few differences in components required for either Ford trucks with 525 lb-ft torque or Navistar International buses with up to 620 lb-ft torque.
They share the same cast iron engine block, either dark grey or medium blue color.
They differ in the power control modules that offer various power ratings between the two engines.
For example, the T444E had up to 620 lb-ft torque for buses, while the PowerStroke only reached 525 lb-ft torque for Ford trucks. However, the PowerStroke engine had higher horsepower than the T444E.
The two engines also differed in some sensors, turbocharger designs, and water pumps.
T444E Engine Production
Over 2 million of the Ford PowerStroke and International T444E engine models were manufactured. The T444E specifically was manufactured from 1994 to 2004.
Navistar International created the T444E in response to increased emissions standards in the U.S. and other countries during the mid-1990s.
To maintain power with cleaner emissions, the diesel engine came equipped with a Hydraulic Electronic Unit Injector system (HEUI). The HEUI system also helped school buses achieve better fuel economy.
As emissions regulation increased, Navistar International discontinued the series and replaced it with the all-new 6.0L VT365 to address emissions mandates.
T444E Engine Transmission Pairs
The T444E diesel engine is commonly paired with the 4-speed Allison AT545 and 5-speed Allison 2000.
T444E Engine Towing Ability
The T444E engine for commercial vehicles has different power ratings, depending on the standard and optional component offerings by the manufacturer.
While the T444E engine has less horsepower than the PowerStroke diesel engine for Ford F-series trucks, the T444E gives school buses and commercial trucks more torque for towing. The low-end RPM of the T444E engine provides higher levels of torque, which allows the engine to easily carry heavy loads.
Towing with a T444E engine paired with the Allison 2000 series transmission is ideal. The AT545 can be swapped out for a more desirable transmission, such as the MT643.
Here is a great video by Jax on his AT545 to MT643 transmission swap on a T444E engine bus:
T444E Engine Life Expectancy
Overall, the T444E is a reliable diesel engine and known to outlast gasoline engines. It has a B50 life of 350,000 miles, which means about 50 percent of the engines last longer than 350,000 miles.
T444E Engine Maintenance Requirements
Engine longevity is possible through proper maintenance of regular oil changes, engine coolant flush, fuel filter replacements, and transmission fluid and filter replacements.
The T444E can use B5 biodiesel fuel to further reduce emissions. It is important to check the OEM engine warranty to ensure that higher-level blends of biodiesel fuel are approved, such as B20.
Extra care is needed for engines that operate under severe or heavy-duty conditions, including excessive idling, dusty environments, frequent hauling, and short trips without reaching full operating temperature.
T444E Engine Problems
The T444E is a reliable engine overall. Given the Navistar International T444E and Ford-Series Diesel PowerStroke engines are similar, they are likely to suffer from many of the same issues.
Mechanics report that the T444E has problems starting in cold weather. Some school bus mechanics recommend plugging in the block heater the night before going out on a winter day. Generally, let the engine warm-up for a few minutes before driving and let it idle for 5 minutes or so before shutting off to help the turbocharger slow down after being revved up.
The vast majority of 7.3L diesel engine issues are relatively simple, inexpensive fixes. Due to their past mass production, engine repairs and rebuilds may be easier to achieve with an abundance of aftermarket parts and mechanic knowledge.
Here are the most common engine issues reported by mechanics:
Injection Pressure Regulator Valve (IPR)
A few things can go wrong with these valves, including damaged seals, damaged wires, or bad sensors.
Injector Driver Module (IDM)
When these modules go bad or suffer from water damage, the engine can stall or run rough. Check for damaged wiring, moisture, or water intrusion.
Diesel Fuel Filter Clogging
A restricted fuel filter will often cause long cranking or a semi-loss of power if the injectors don’t get needed fuel.
Lift Pump Problems
A lift pump failure will prevent the engine from starting. Check the fuel bowl for fuel before and while cranking. If no fuel is in the fuel bowl, fill the bowl with clean fuel. If it starts, replace the pump.
Injector Control Pressure (ICP) Sensor
A bad sensor causes the engine to cut in and out. If you detect oil in the ICP connector, the sensor may be bad or reaching a failure point. If oil has permeated the wires, it is recommended to replace the ICP sensor pigtail, as well.
Diesel Fuel Heater
The fuel heater can short out and blow a fuse, which disables the powertrain control module. The issue may clear up when disconnecting the fuel heater, replacing the fuse, and restarting.
T444E Engine Comparisons
T444E vs DT466 / DT466E / MaxForce DT
Navistar International already had other engines in production when it began making the 7.3L V8 T444E diesel engine in 1994. The 7.6-liter six-cylinder diesel turbocharged engine series (DT466/466E/MaxxForce) had already been in production for 20 years, and they were popular engines for school buses.
The DT466/466E was referred to as “The Legend,” because it had a good reputation for its long-running performance and reliability.
By the mid-1990s, the DT466 engine was undergoing a design upgrade in response to regulations for vehicle emission reductions. Navistar International changed the design from a mechanical injection system to an electronic injection system for cleaner emissions and greater fuel economy.
The model name changed to DT466E to indicates with the “E” that it had an electronic control system to maintain power with cleaner emissions. The first of those systems was a Hydraulic Electronic Unit Injector system (HEUI), launched in 1995. In 2004, the G2 “Generation 2” injection system debuted, which was an improved and updated HEUI system. Beginning in 2007, Navistar International retired the DT466/DT466E namesake in favor of new emissions-compliant engine family, called the MaxxForce DT.
School bus mechanics differ in their favorites picks among the T444E vs. DT466/466E. Mechanics report that it is relatively easy and inexpensive to find DT466/466E/MaxxForce replacement engines and parts because there were produced in large numbers. The biggest flaws are the engine’s size and weight. Older versions of the DT466 weigh 1,425 pounds, while later versions of the MaxxForce DT weigh as much as 1,900 pounds with its emissions control devices and sometimes even two turbochargers.
Many believe the T444E was likely more popular when it came to price comparisons because it was often marketed at lower prices. However, when it came to comparisons of engine power, the DT466/466E was more popular among school bus mechanics. For example, a 230hp T444E engine and a 230hp DT466E engine are similar in performance to a point. The T444E may sufficiently haul a lightweight vehicle or smaller school bus weighing a maximum of 23,000 pounds, but the DT466E is considered more powerful for hauling bigger buses and heavier loads.
School bus mechanics also mention the T444E has a harder time starting up than the DT466E, especially in colder weather.
T444E vs 5.9 Cummins
Cummins already had a competitive diesel engine in production when the Navistar International T444E launched into production in the mid-1990s. The Cummins 5.9L (or B Series diesel engines) went into production in 1984 for use in agricultural equipment. By the end of production in 2007, the Cummins 5.9L had gone through a few iterations for reduced emissions, and it was a popular engine for Types C and D school buses.
While the Navistar International T444E had a strong association with Ford F-Series trucks, the Cummins 5.9L had strong brand associations with RAM medium- and heavy-duty trucks. A version of the Cummins 5.9L diesel engine was featured in Dodge pickup trucks.
Cummins’ first engine model, known as the 6BT or 12-valve 5.9L, was a popular alternative to large gasoline V8 engines, such as the T444E. Despite its smaller size, Cummins turbocharged diesel engines could produce significant power with decent torque at low engine speeds.
Cummins diesel engine series went through several design changes as the manufacturer complied with emission reduction laws by U.S. Federal, state and local governments. Cummins worked with school bus manufacturers, such as Blue Bird and Thomas Built, to build vehicles that would be safe and clean enough to transport students.
In 1998, Cummins replaced the 6BT 12-valve 5.9L with the 24-valve 5.9L ISB (Interact System B), which was designed for improved fuel economy and emissions. The ISB model used electronically controlled Bosch fuel systems, unlike the 6BT systems which were mechanical.
The 1996-1998 California model engines were fitted with exhaust gas recirculation (EGR) to meet the California Air Resource Board’s (CARB) stringent Nitrogen Oxides (NOx) standards. For further environmental protection, bus operators shifted to biodiesel fuels. Some high horsepower Cummins engines with certain fuel systems can use industry-approved biodiesel.
School bus mechanics report that the Navistar International T444E and Cummins 5.9L are similar in their abilities to sufficiently run small-to-medium size school buses. For more demanding drives, such as bigger school buses and heavier loads, mechanics tend to favor the Navistar International DT466/466E (see above).
If maintained properly, mechanics report that the T444E can reach higher mileage over its lifetime than the Cummins 5.9L. The mechanical 5.9L was given a life expectancy of 350,000 miles without catastrophic failure, but some school bus owners will tell you that range is conservative. Owners of a used school bus with a Cummins 5.9L will likely need to replace some expensive fueling parts long before hitting that kind of high mileage.
Mechanics the Cummins 5.9L has enough durability to outlive multiple transmissions throughout the course of its life. It’s not so much about the automaker’s inability to build a quality diesel-rated transmission, but rather the engine manufacturer’s I-6 power plant turning out so much low-rpm torque.
When it comes to common engine issues, mechanics report the T44E has more simple, inexpensive fixes (see above). Common issues with the Cummins 5.9L are more severe, such as exhaust manifold leaks and engine block cracks.