Cummins 6BT 12 Valve Engine: Specs, Problems, and Reliability. The Cummins 6BT is the most famous truck engine of the B series. The 5.9 l Cummins engine was the first diesel engine used in full-size pickup trucks as an alternative to the big V8 gasoline engines. The production was started in 1984. It was designed as an engine for Case agricultural equipment. In the future, the 6BT was widely used in light, medium, and some heavy-duty trucks and buses. The turbocharged 12 Valve Cummins engine found huge popularity in 1989-1998 model year Dodge Ram pickup trucks for a massive torque at low rpm and all engine speed range, and a better fuel mileage compare to Dodge’s gasoline V8 engines.
The engine has the smaller brother using better fuel economy – 3.9 L 4BT engine. They both have the same architecture (inline engine) but a different amount of cylinders. The Cummins 6BT engine is inline six cylinders 5.9-liter turbocharged diesel engine (turbodiesel). The engine has a cast-iron engine block and cylinder head. The valvetrain is 12 valve OHV (2 valves per cylinder), solid tappets. In this order, the engine is called a 12-valve Cummins very often. There is a set of timing gears at the front end of the engine (no chains or belts).
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Cummins 6BT 12 Valve Engine: Specs, Problems, and Reliability
An oil pump and a fuel pump are driven by gears also. The engine has a mechanical and reliable injection pump (easy for tuning) and fuel injectors. Before 1994 the engines were equipped with Bosch VE44 rotary injection pump, but some early versions have CAV rotary injection pump. 1994+ engines have Bosch P7100 injection pump. All 5.9 l engines were equipped along with a turbocharger and since 1991 together with air-to-air intercooler. Holset made all turbochargers – Holset H1C (1989-1993), Holset WH1 (1994 ), Holset HX35 (1994-1998). For helping to start the engine in cold weather, the grid heater is mounted on the intake manifold as opposed to a traditional glow plug system.
The manufacturer offered the engine along with such transmissions as Chrysler 47RH (4 speed automatic), New Venture NV4500 (5-speed manual), and GETRAG G360 (5-speed manual). The 12 valve engine was produced before 1998 and after that was replaced by the new 24-valve engine along with the Bosch high-pressure Common Rail fuel injection system – 5.9 L ISB Cummins.
Cummins 6BT 12 Valve Engine: Specs
| Manufacturer | Cummins |
| Production years | 1989-1998 |
| Cylinder block material | Cast Iron |
| Cylinder head material | Cast Iron |
| Fuel type | Diesel |
| Fuel system | Direct Injection (DI), mechanical injection pump |
| Configuration | Inline |
| Number of cylinders | 6 |
| Valves per cylinder | 2 |
| Valvetrain layout | OHV |
| Bore, mm | 4.02 inch, 102 mm |
| Stroke, mm | 4.72 inch, 119 mm |
| Displacement, cc | 359 cubic inches, 5.9 liters |
| Type of internal combustion engine | Four-stroke, turbocharged |
| Compression Ratio | 17.0 : 1 |
| Power, hp | 160 – 215 hp /2,500 |
| Torque, lb ft | 400-440 lb-ft (542-597 Nm)/1,600 |
| Engine weight | 1100 lbs, 499 kg, dry |
| Firing order | 1-5-3-6-2-4 |
| Engine oil weight | SAE 15W40 diesel oil with a dual rating of at least CF4 and at least SG |
| Engine oil capacity, liter | 12 qts (11.4 liters) with filter. |
| Oil change interval, mile | 6,000 (10,000 km) or 6 month (3000 miles for severe duty) |
| Applications | Dodge Ram pickup trucks, buses, marines, agricultural equipment, construction machinery |
12 Valve Cummins Reliability and Problems
The cast iron engine block and the head are the basis for excellent reliability and longevity. There are not a considerable amount of electronics and nothing fancy. The 6BT is a straightforward diesel engine together with a mechanical pump and injectors. It makes it undemanding to fuel quality. The 12 Valve Cummins engines are known for starting quickly in any weather condition also.
The engine has some faults. Among them is a clogged grid heater. It is mounted between the air tube and intake manifold. Gradually, the heating element is covered using soot caused restricted airflow into the intake manifold. In this case, an engine takes a little longer to start than usual and sometimes dies while idling or at low rpm’s, consumes more fuel. The other problem together with the 12-valve engine is called The “Killer Dowel Pin,” or KDP.
The engine has a steel dowel pin pressed into the block located near a bolt between timing gear and fuel pump gear. Engine vibration slightly pushes this pin to back out. The pin may fall between the timing gears and cause massive damage to the engine (blend valves, brake pistons, and timing gears). There are a few very cheap solutions to prevent the engine from this dramatic outcome on the market.
