It isn’t easy to pick the right diesel engine for your current and future needs. Not only do you have fuel costs to consider, but there are also power and durability issues to manage.
When choosing a truck engine, it’s easy to look at brands like GMC, Peterbilt, or BMW first. If you fall into that trap, you’ll miss the potential benefits of working with a Caterpillar product.
Caterpillar (or “Cat” for short) builds reliable diesel engines for a variety of vehicles. The 3406 has more than two decades of experience on the road, but anything in the 6NZ designation is worth considering if you need extra power.
What Is 6NZ?
The 6NZ is a serial number prefix used to identify an engine series from Caterpillar. Although the brand is known for creating heavy equipment, it also creates engines for semi-trucks, big rigs, and other large haulers on the road or in the water. It is a comparable design to the C15 and the 3406E diesel engines.
Caterpillar is based in the United States. Cat manufactures several heavy equipment and industrial vehicles, but they also produce several engines and replacement parts.
The 6NZ is a series of different engines that can be used in several applications. Its most famous creation in this designation is the C15 lineup, which replaced the 3406 series.
You can purchase the original 3406 or go with the updated 3406E for your needs, but the engines are intended for use in large vessels. It can be used alone or in a group to generate massive power. The C15 is meant more for land vessels.
If you’re on a yacht, freight transport vessel, or cruise ship, there’s an excellent chance that a Cat 3406 is delivering the power needed for forward momentum.
Trucks typically have a C15 engine installed from the 6NZ series.
The last engines outside of those for off-highway machinery were built in 2010, but the current 6NZ series is still going strong.
Caterpillar never made public what engine prefix numbers went into specific vehicles, so it is unknown who has these engines, where they are, and if anyone is still using them.
A Closer Look at 6NZ Caterpillar Engines
Cat engines with the C15 model were given several different engine prefixes, even during the same production year.
When Caterpillar was building 99,900 6NZs, they also produced 30,000 MBN and 18,5000 9NZ from 1998 to 2002. These engines even use the same fault code tables.
Here’s a closer look at the various engine prefixes, the engine model associated with them, and when they were available to the public.
| Engine Prefix | Engine Model | First Built | Last Built | Quantity Built | Model Years | Additional Notes |
| 6NZ | C15 | July 1998 | June 2005 | 99,900 | 1998 to 2002 | Same fault codes as 9NZ, MBN, and EGH |
| 9NZ | C15 | June 2005 | February 2009 | 18,500 | 1998 to 2002 | Same fault codes as 6NZ, MBN, and EGH |
| MBN | C15 Bridge | December 2001 | February 2003 | 30,100 | 1998 to 2002 | Same fault codes as 9NZ, 6NZ, and EGH |
| EGH | C15 ACERT | December 2002 | October 2004 | Under 300 | 1998 to 2002 | Same fault codes as 9NZ, MBN, and 6NZ |
| BXS | C15 ACERT | March 2003 | December 2004 | 39,000 | 2003 | First actual engine using ACERT technology |
| MXS | C15 ACERT | March 2003 | July 2006 | 100,000 | 2004 to 2006 | Most popular ACERT engine |
| NXS | C15 ACERT | July 2006 | April 2009 | 33,000 | 2004 to 2006 | Same engine as the MXS – ran out of serial numbers |
| RKS | C15 ACERT | September 2008 | January 2009 | Under 100 | 2004 to 2006 | Same fault code as MXS and NXS |
| SDP | C15 ACERT | January 2005 | March 2009 | 22,700 | 2007 to 2010 | Last C15 engine with this prefix |
As you can see, the C15 engine from Caterpillar comes in three different versions. It has the standard C15 setup from the original build, the “bridge” that connects the transition from the first version to the final, and then the ACERT engine.
ACERT is a proprietary Caterpillar technology that meets the 2004 and 2007 emission standards set by the Environmental Protection Agency. ACERT stands for “Advance Combustion Emission Reduction Technology.”
Cat designed the C15 to be the replacement for the 3406E as they phased it out, keeping the popular 15.0L engine and its big bore design.
What Is the Difference Between the C15 and the C15 ACERT?
Most people believe that the primary difference between the original C15 engine and the C15 ACERT is the inclusion of an extra turbo. Although that is a key difference between the two designs, there is more to it than meets the eye.
One of the best improvements that Cat included with the C15 ACERT engine involves its piston design. Instead of implementing a two-piece aluminum skirt, the ACERT uses a one-piece steel option.
If you’re interested in using a C15 ACERT for your rig, boat, or heavy equipment, you’re better off looking for one of the later models.
Although they’re all strong and reliable, the ones that came off the production line first had problems with their rocker studs breaking. The exhaust manifolds also had stud-related problems – or just broke.
The fuel injectors in the C15 lineup are known to fail as time passes, even with proper maintenance. Inspecting them should be part of the regular maintenance needs for those using this engine.
Here are the specs of the C15 ACERT to review.
| Fuel Requirements: | Diesel only |
| Liter: | 15.2L engine |
| Cubic Inch Displacement: | 928 |
| Stroke: | 6.732 inches (171 mm) |
| Cylinder Configuration: | L6 |
| Cylinder Bore Diameter: | 5.4 to 5.402 inches (137.16 mm to 137.21 mm) |
| Engine Review | SOHC Electronic, Similar to 3406E |
| Compression Ratio: | 18.1 |
| Available Power: | 435 HP to 625 HP at 2100 RPM |
| Weight: | 2,890 Pounds |
| Oil Capacity: | 41 Quarts |
The durability of the C15 ACERT engine is impressive. It goes for about 20,000 miles before needing an oil change, has an expected engine life of one million miles, and incorporates a 300,000-mile particulate filter.
When you find the right combination of oil, fuel, and driver management with the C15 series, you have a powerful and efficient way to transport cargo. The same outcomes apply if you’re operating one of the older 3406 engines out at sea.
Even if you can only find a rebuilt one to use for your needs, it’s worth considering an investment in this hard-working engine.
Best Oil to Use for Hard Working Diesel Engines
As I’ve driven trucks over the years, I’ve seen mechanics use (and used myself) several different diesel oil products. Some seem to work great, while others make you wonder what you were thinking.
The one that works the most consistently for me is Shell Rotella T5 Synthetic. When you’re putting in 41 quarts or more into your engine for a complete change, you need something that’s cost-effective without compromising the quality of your engine. After all, your ability to roll down the road with cargo is how you make money.
I like how the Rotella guards against oil breakdown when you’re driving all the time. It delivers remarkable protection for those times when you need more resistance to stress or heat. It also helps to control engine deposits so you can push the limits a little when the need arises.
The triple protection tech also safeguards against premature wear and tear while preventing unwanted deposits from forming. According to Shell’s testing, the results are 37% better than the API CK-4 standard.
It doesn’t take long to figure out that conditions aren’t always favorable or predictable when driving a rig. The T5 provides better cold-cranking properties because it reaches your critical engine components faster when you’re ready to start your day.
It is suitable for any engine requiring an API of CH-4, CI-4, CJ-4, or CK-4 diesel oil with this viscosity rating.
Is It Worth Investing in a 6NZ Engine?
The Caterpillar 6NZ engine series with the C15 design delivers an impressive amount of power while producing less soot and consuming less fuel. It’s meant to run lean and deliver plenty of boost with its compression-friendly design. Precise injection ensures fuel is used efficiently in all conditions.
Back in my college days, I worked in the headquarters of one of the largest shipping and transport companies in the United States. Truckers came in daily, the smell of oil and diesel was always in the air, and lots of engines needed servicing.
I wasn’t the mechanic. I was the janitor.
One day, a truck came limping into the shop. The driver said he thought it had blown a piston, but the mechanic looked at him skeptically. “These Cat engines don’t do that,” he said. “It’s got to be something else.”
The guy waved me over to help. “Crawl up on top to see if there’s something stuck in there,” he said. “I’ll check from below.”
Yeah – there was something stuck in there. The driver had apparently run into a flock of birds somewhere, and one had gotten stuck along the drivetrain. Even though it caused the engine to heat, there was no damage to it.
The mechanic showed the driver the problem. “There’s your blown piston, Amigo,” he said.
When I finally got into the trucking business myself for a bit, I made sure my rig had a C15 in it. The turbo, compression, and responsiveness are everything you’d expect it to be.