Cummins 4BT 3.9L Engine Specs, Problems & Reliability

Cummins 4BT 3.9L Engine 

Here in this post, I have gathered information about the Cummins 4BT 3.9L Engine from its official website, including its specifications, Problems, and Reliability.

We believe in providing reliable information to our readers, therefore we prefer to obtain information on the Cummins 4BT 3.9L Engine from authentic sources.

This article, which has been updated, has all the information you require about the Cummins 4BT 3.9L Engine.

Cummins 4BT 3.9L Engine 

The Cummins 4BT is a water-cooled turbodiesel inline-four-cylinder engine.

The most popular B-series engines are the 3.9-litre straight-four and the 5.9-litre straight-six (12-valve Cummins). Other options include four-cylinder engines with displacements of 3.3 and 4.5 litres.

The engine block is made of cast iron and features engine bores that were machined into the iron.

The application-specific differences among 4BT engines lie solely in the gearbox adapter plate, as all 4BT engine blocks are identical.

OHV refers to an overhead valve valvetrain, which is used in the engine. In the front of the engine, a camshaft is installed in the block and powered by the crankshaft via gears (as well as the oil pump).

Valve opening and closing are accomplished by the camshaft’s pushrods and solid tappets operating on the rocker’s arms.

Cast iron is also used for the cylinder head. The apertures for taking in air and releasing exhaust are located on opposite sides of the device (crossflow cylinder head).

Every one of the eight cylinders has its own pair of valves. Injecting fuel directly into the cylinders mechanically is a 4BT characteristic.

In the earliest models, the mechanical injection pump, model P7100, is gear-driven off of the camshaft.

Firing order1-3-4-2
Engine oil weight
Engine oil capacity, litre
10 qts (9.5 litres) with filter
Oil change interval, mile
6,000 (10,000 km) or 6 month
Industrial equipment, commercial vehicles (step vans, trucks), marines and boats
Production years
Cylinder block material
Cast Iron
Cylinder head material
Cast Iron
Fuel type
Fuel system
Direct Injection (DI), mechanical injection pump
Number of cylinders
Valves per cylinder
Valvetrain layout
Bore, mm
4.02 inch, 102 mm
Stroke, mm
4.72 inch, 119 mm
Displacement, cc
239 cubic inches, 3.9 litres
Type of internal combustion engine
Four-stroke, turbocharged
Compression Ratio
17,5 : 1 (4BT)
16.5 : 1 (4BTA)
18.5 :1 (4B)

Cummins 4BT 3.9L Engine Problems & Reliability

Since the 3.9-litre engine is so versatile, it can be had for next to nothing. The B-series engines can function with few electronic components, are easily repaired, and cost little to nothing to rebuild.

Newer diesel with electric VP pumps are less reliable and more difficult to modify than older diesel with a P-pump.

Nonetheless, the 4BT is a big diesel engine that has been around for a long time and shows signs of wear. It’s loud, unsteady, and smells like an old diesel engine.

In addition to its height and weight, the 4BT also requires space for an intercooler and pipes, making it challenging to fit under the hood of a compact vehicle.

However, its weight places additional strain on the front suspension, which might affect the handling of a smaller 4×4 vehicle. This is not enough power for a full-size truck or SUV.

Cummins 4BT 3.9L Engine Review 

Cummins 4BT engine 3.9L is a turbocharged diesel that was produced between 1984 and 2006. The engine is a 4-cylinder with a displacement of 3.9 liters. The 4BT engine is known for its reliability, durability, and fuel efficiency. It is compact and lightweight, making it an ideal choice for engine swaps. For a full review, please check this YouTube video Here.

Cummins 4BT 3.9L Engine FAQ

How much HP can a 4BT Cummins make?

What are the specifications of the 4BT Cummins engine’s output? The 105 hp and 265 lb-ft of torque from a 4BT Cummins engine can be had at 2,300 rpm and 1,600 rpm, respectively.

Because of turbocharging and direct fuel injection, this is possible.

Is Cummins 4BT a good engine?

The 4BT power plant is dependable and extremely durable. It has been said time and time again that the Cummins 6BT is the most dependable diesel engine ever produced.

The 4BT is equally as trustworthy an engine as the 6BT it is based on because it uses the same components.

Why is the 4BT so popular?

The 4BT Cummins, to be specific. It has become a household name in the world of engine swaps due to its compact dimensions, copious amounts of low-rpm torque, overland-friendly fuel efficiency, and decades-long endurance.

What mpg is a 4BT Cummins?

If your truck only gets 15 mpg now, the conversion’s fuel savings aren’t going to be enough to cover the cost. The majority of the real-world estimates we’ve seen have been in the 17–21 mpg area.

Notify of

Inline Feedbacks
View all comments