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CAT 3116 & CAT 3126 Diesel Engine

Caterpillar introduced the CAT 3126 engine in 1997 as its first electronic mid-range diesel engine. The CAT 3126 is a turborcharged 7.2L inline 6-cylinder diesel engine used to power medium-duty buses, dump trucks, tow trucks, fire trucks, ambulances, and RV motorhomes. It is also closely associated with the CAT 3116 diesel engine, which is primarily used in marine applications. The CAT 3116 is a slight variation of the CAT 3126.

This CAT 3116 and CAT 3216 diesel engine 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 CAT 3116 and CAT 3216 diesel engine including:

  • Engine Overview
  • Engine Specs
  • Towing Capacity
  • Life Expectancy
  • Maintenance Requirements
  • Typically paired transmissions
  • Common engine problems
  • Engine comparisons to the DT466 / DT466E and T444E

CAT 3116 & 3216 Diesel Engine Overview

The CAT 3126 diesel engine came to market just as regulation went into effect to improve air quality and reduce emissions in the United States, Canada, and other countries. For Caterpillar to better comply with escalating emissions regulation, the manufacturer released two other versions of the CAT 3126 over seven years of the series production. All engine versions were basically the same, and they all included a hydraulically activated electronic control injector (HEUI) designed for staged fuel distribution to improve engine combustion and reduce emissions. 

The two engine variants differed with improvements to electronic components and fuel systems. The first variant, called the CAT 3126B, was introduced in 1998 with an improved HEUI system and new fuel injectors to achieve higher horsepower and torque ratings. The injectors use CAT’s pre-injection metering (PRIME) system, which provides a short injection of fuel ahead of the delayed main injection. This system helped reduce nitrogen oxide (NOx) and noise emissions. The second variant, called the CAT 3126E, was introduced in 2002 as an intermittent diesel engine for meeting even stricter emissions regulations slated for 2004. The CAT 3126E diesel engine featured a rudimentary Advanced Combustion Emissions Reduction Technology (ACERT), which is an air/fuel management system to control emissions. 

In 2004, Caterpillar ended production of the CAT 3126 and replaced it with the CAT C7 diesel engine. The CAT C7 featured even more electronics and emissions reduction equipment while offering a wider range of horsepower (from 210 hp to 360 hp) and torque capacities. 

Mechanics report that if properly maintained the CAT 3126 is a very reliable diesel engine. However, it had an unfair bad reputation, because it was associated with issues from its parent CAT 3116 diesel engine. The two engines shared the same engine block design, but only the CAT 3116 reportedly had issues of cracked engine blocks resulting from high stress to powerboats. The engine blocks were prone to cracking when the engine ran over its red line to level out boats on choppy waves.

3116 & 3216 Engine Specs

Engine variationsProduction YearsHorsepowerTorque
CAT 3126
CAT 3126B
CAT 3126E
1997 to 1998
1998 to 2001
2002 to 2004
Minimum: 175 hp @ 2400 RPM
Maximum: 300 hp @ 2200 RPM
Minimum: 420 lb-ft @ 1440 RPM
Maximum: 860 lb-ft @ 1440 RPM

CAT 3116 & CAT 3216 Transmissions

The CAT 3126 diesel engine was paired with Allison generation 3 transmissions, either the 2000 series or 3000 series. These automatic transmissions included more sensors and diagnostic capabilities than previous models. Mechanics report sometimes transmissions are swapped with Eaton transmission models in the aftermarket. 

The CAT 3116 diesel engine for marine applications was paired with the MG5050 with variable-speed gear ratios. The fastest transmission, the MG507-1, is heavier at 350 pounds.

Towing with a CAT 3116 or CAT 3216

The CAT 3126 diesel engine was built to accommodate medium-duty vehicles and a maximum tow capacity of 9,000 pounds. Upgraded horsepower and torque were optional for more rigorous towing.

The CAT 3116 diesel engine for marine applications had lower horsepower, and some boats were equipped with twin engines for more power on the water.

CAT 3116 & CAT 3216 Diesel Engine Life Expectancy

The CAT 3126 and CAT 3116 diesel engines could reach 200,000 miles before requiring a major repair or rebuild. That kind of engine life expectancy is considered low range when compared with competitor diesel engines.

CAT 3116 & 3126 Engine Maintenance Requirements

Extra care and high-quality fluids are needed for CAT 3126 diesel engines, especially when operating under heavy-duty conditions (i.e., excessive idling, dusty environments, frequent hauling, and short trips without reaching full operating temperature). The CAT 3116 diesel engine for marine applications requires different maintenance depending on usage measured in hours.

Engine variationsNormal conditions
CAT 3126 diesel engine for medium-duty trucksOil capacity: 22 quarts
Engine oil & air filter: 6,000 miles/6 months
Fuel filter: 15,000 miles/6 months
Engine coolant: 200,000 miles/24 months
Transmission fluid & filter: 30,000 miles

CAT 3116 & CAT 3126 Common Engine Problems

The CAT 3126 diesel engine was adjusted over time to accommodate strict emissions regulations. Many mechanics have reported several issues with the components intended for reduced emissions. 

  • Hydraulically activated electronic control injector (HEUI) – If not maintained and lubricated properly, mechanics report the HEUI could develop issues. Older engines (2002 model year) sometimes have faulty HEUI fuel pumps.
  • Advanced Combustion Emissions Reduction Technology (ACERT) problems – The ACERT system is prone to numerous issues. For example, mechanics report clogged diesel particulate filters, as well as clogging of the turbocharger inlet.
  • Valves – Valve drop is an issue reported by mechanics. Valve drops are more common on heavy-duty machines and equipment, due to the engine’s rigorous use. It’s recommended that vehicle owners check valves as part of a routine maintenance schedule.
  • Other common issues – Mechanics list other issues associated with the CAT diesel engine, including cracked cylinder heads (mostly CAT 3116 models), crankshaft failures, over fueling, lack of oil pressure and scored pistons/liners.

CAT 3116/3126 vs. CAT C7

After the CAT 3116/3126 diesel engine series ended production in the early 2000s, Caterpillar introduced the inline 6-cylinder CAT C7 diesel engine series in 2003 for use in heavy-duty vehicles with gross vehicle weight (GVW) up to 33,000 pounds. 

The CAT C7 diesel engine powered box trucks, tow trucks, fire trucks, tractor-trailers, RV motorhomes, and large school buses. It was also used in severe-duty equipment for agriculture, construction, and mining industries. To help power a wide range of heavy-duty vehicles, the diesel engine provided original equipment manufacturers (OEMs) with a range of horsepower and torque capacities. The engine was available in 8 different horsepower ratings (from 210 to 360 hp), as well as various torque ratings (520 to 925 lb-ft). The highest horsepower version required an optional dual turbocharger.

Both CAT engine series came with a hydraulically activated electronic control injector (HEUI) designed for staged fuel distribution to improve engine combustion and reduce emissions. The CAT 3126 diesel engine also featured an early version of Advanced Combustion Emissions Reduction Technology (ACERT), which is an air/fuel management system to control emissions. The CAT C7 engine included improvements to both HEUI and ACERT systems.

New regulation in 2007 dictated the use of Ultra Low Sulfur Diesel (ULSD) for fueling newly produced heavy-duty vehicles and super-duty machinery. In response to the fuel change, Caterpillar upgraded the CAT C7 engine with a new common-rail fuel injector system for pumping different kinds of liquid fuel.

Production for both CAT 3116/3126 and C7 diesel engine series lasted only a few years. By 2009, Caterpillar no longer wanted to invest money and effort to keep upgrading engines for new low emissions mandates that went into effect in 2010.

Feature comparisonCAT 3126 diesel engineCAT C7 diesel engine
Production years1997 to 1998 CAT 3126
1998 to 2001 CAT 3126B
2002 to 2004 CAT 3126E
2003 – 2009
HorsepowerMinimum: 175 hp @ 2400 RPM
Maximum: 300 hp @ 2200 RPM
Minimum: 210 hp @ 1800 RPM
Maximum: 360 hp @ 2200 RPM
TorqueMinimum: 420 lb-ft @ 1440 RPM
Maximum: 860 lb-ft @ 1440 RPM
Minimum: 520 lb-ft @ 1800 RPM
Maximum: 925 lb-ft @ 2200 RPM

CAT 3116 / 3126 vs. DT466 / DT466E

The Navistar International DT466/DT466E/MaxxForce diesel engines were in production long before and after the introduction of CAT 3116/3126 diesel engines. The Navistar diesels were designed for heavy-duty vehicles and severe-duty equipment, while the CAT 3116/3126 were more appropriate for medium-duty vehicles and marine applications (mostly CAT 3116).

Unlike the CAT diesel engines, the Navistar International diesel series includes a wet-sleeve cylinder design, which enhances engine durability and serviceability. The wet-sleeve design allows the engines to be rebuilt to factory specifications, sometimes without even removing the engine from the vehicle. Some mechanics claim the wet-sleeve design also gives DT466-equipped vehicles greater longevity, sometimes 700,000 miles before requiring a major repair or rebuild. 

Fuel management components within the CAT 3116/3126 diesel engines evolved over time to meet escalating emission reduction regulations in the late 1990s and early 2000s. Caterpillar eventually replaced the engines with an all-new CAT C7 diesel engine to better meet more rigorous regulations in 2004. Navistar International had two upgrades (DT466E in 1995 and MaxxForce in 2007) to address the same escalating emissions regulations. 

Mechanics report the CAT diesel engines had more issues with its componentry, such as HEUI and ACERT system failures. Mechanics list other issues associated with the CAT diesel engines, including cracked cylinder heads (mostly CAT 3116 models), crankshaft failures, over-fueling, lack of oil pressure, and scored pistons/liners.

Due to their long production run, the DT466/DT466E/MaxxForce engines and components tend to be more plentiful in the aftermarket.

Feature comparisonCAT 3126 diesel engineDT466/DT466E/MaxxForce
diesel engines
Production years1997 to 1998 CAT 3126
1998 to 2001 CAT 3126B
2002 to 2004 CAT 3126E
DT466: 1971 to 1994
DT466E: 1995 to 2007
MaxxForce DT: 2007 to 2015
HorsepowerMinimum: 175 hp @ 2400 RPM
Maximum: 300 hp @ 2200 RPM
Standard: DT466: 250 hp @ 2,400 RPM
DT466E: 275 hp @ 2,4000 RPM
MaxxForce DT: 300 hp @ 2,200 RPM
TorqueMinimum: 420 lb-ft @ 1440 RPM
Maximum: 860 lb-ft @ 1440 RPM
Standard: DT466: 660 lb-ft @ 1,600 RPM
DT466E: 800 lb-ft @ 1,600 RPM
MaxxForce DT: 860 lb-ft @ 1,300 RPM

CAT 3116/3126 vs. T444E

The CAT 3116/3126 and Navistar International T444E diesel engines were produced approximately the same years. Hence, they both evolved in response to increased emissions standards in the U.S. and other countries during the late 1990s and early 2000s. Due to the shorter production years of both engines, aftermarket components tend to be scarcer and more expense to repair.

To maintain power with cleaner emissions, both the CAT 3116/3126 and T444E diesel engines were equipped with their own versions of a Hydraulic Electronic Unit Injector system (HEUI). Another similarity between the two engines is the absence of a wet-sleeve design, which makes them both harder to repair and rebuild than competitor diesel engines. 

They differed in the vehicles that they powered. The CAT 3116/3126 diesel engines were built for medium-duty vehicles and marine equipment. The Navistar International T444E or Power Stroke, is best known for powering Ford Super Duty 250/350 diesel trucks, Ford Excursion sport utility vehicles and E-series vans. The T444E engine also was part of the bus chassis for Navistar International Type C school buses and other medium-duty vehicles. 

Mechanics report that the Navistar International T444E has problems starting in cold weather. Some mechanics recommend plugging in the block heater the night before going out on a winter day. Allow the engine to warm up before driving, and let it idle for a few minutes before shutting off to help the turbocharger slow down after being revved up. 

As air quality regulation increased, Navistar International discontinued the T444E series and replaced it with the all-new 6.0L VT365 to address emissions mandates. For the same reasons, production for the CAT 3116/3126 diesel engine series lasted only a few years. Even its replacement diesel engine, the CAT C7, lasted only a few production years. By 2009, Caterpillar no longer wanted to invest money and effort to keep upgrading engines for new low emissions mandates that went into effect in 2010.

Feature comparisonCAT 3126 diesel engineT444E diesel engine
Production years1997 to 1998 CAT 3126
1998 to 2001 CAT 3126B
2002 to 2004 CAT 3126E
1994 to 2004
HorsepowerMinimum: 175 hp @ 2400 RPM
Maximum: 300 hp @ 2200 RPM
Standard: 184 hp @2,200 RPM
Optional: 238 hp @ 2,300 RPM
TorqueMinimum: 420 lb-ft @ 1440 RPM
Maximum: 860 lb-ft @ 1440 RPM
Standard: 460 lb-ft @ 1,400 RPM
Optional: 620 lb-ft @ 1,400 RPM
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