CAT C15: The Engine For Your Industrial Needs?

by Conner Mckay

The CAT C15 from Caterpillar is a popular industrial diesel engine. From agricultural applications to drill rigs, it’s a reliable and capable engine for many industrial needs. It has even found popularity amongst truckers.

Unfortunately, while they still produce it, it’s mostly for off-highway use. We’ll discuss the engine’s strengths and weaknesses so you can decide whether it’s the engine for you or not. And we’ll also talk about why this engine is dying on the road.

CAT C15: What’s The Spec?

Of course, the first thing we should do is take a look at the spec sheet. Everyone loves a spec sheet. The C15 is an inline-six cylinder diesel engine, with a displacement of 15.2L or 928ci.

All this translates to 580 horsepower and a whopping 1,958lb-ft of torque. However, the power output may vary depending on what you use this engine for, which we’ll get into after this.


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They introduced the engine in 1999 and were discontinued in 2010. But don’t worry, rebuild kits are available and replacement parts are plentiful. The C15 boasts a 5,000-hour DPF (Diesel Particulate Filter) service interval, with a DEF (Diesel Emission Fluid) capacity of 93.7 liters.

On top of that, Caterpillar claims that the CAT C15 has a 500-hour maintenance interval. Meaning fewer services, so the engine can run longer, and it keeps costs low. Now, keep in mind that the C15 actually has several variations. This affects their power output and emissions.

The CAT C15 Engine Family

The C15 actually has a total of 10 variations. These mostly have minor differences, with some only different in serial numbers. But there are three that are quite different:

  • Original C15, that has either a 6NZ or 9NZ serial number.
  • C15 “Bridge”, has the MBN serial number and was introduced in 2001. Essentially still the same engine but with an electronic wastegate and other minor improvements to meet emissions regulations (to learn more, check out our explainer on do you need a catalytic converter).
  • C15 ACERT, twin-turbo variation of the C15, meets the 2004 & 2007 EPA emission standards.

So, the original C15 was produced until 2009. Then the less popular “Bridge” (MBN) engine came along in 2001 until 2003. This was intended to meet new emissions regulations at the time before they built the almost-entirely different ACERT.

Think of the bridge engine as sort of a minor facelift of the C15. But the result was slightly less power output at almost 10% less.

Afterward, they introduced the C15 ACERT variant. ACERT stands for Advance Combustion Emission Reduction Technology. Sounds like utter nonsense, but it consists of clean-induction technology, variable valve actuation for the turbocharger, and a diesel particulate filter.

All this means that the C15 ACERT makes less emission and meets the EPA’s demands in 2007. Other upgrades include adding a second turbocharger to further improve emissions and efficiency, and a better piston design featuring a two-piece aluminum skirt.

The ACERT makes anywhere between 440 to 595 horsepower, and a maximum of 1,958lb-ft of torque depending on the specs and applications. For the full engine spec, see below:

Full Engine Specs

  • Engine: 15.2-liter (928 cubic-inch), four-stroke direct-injection inline-six diesel, with either a single turbo or twin-turbo in ACERT variant.
  • Bore x Stroke: 137mm x 165mm (5.4-inches x 6.5-inches)
  • Compression Ratio: 17.0:1 in early versions, and 18.2:1 in ACERT variant.
  • Power Output: Between 440 – 595 horsepower, and 1,188 – 1,958lb-ft of torque depending on engine variant and application.
  • Weight: 3,673 net dry weight on the heaviest variant.
  • Dimensions (LxWxH): 56.6 x 38.1 x 49.1 inches.
  • Coolant Capacity: 75 liters (20 gallons).
  • Engine Oil Capacity: 48.4 liters (51.1 U.S. quarts).
  • Oil Change Interval: 500 hours.

What’s The Engine For?

Caterpillar lists down around 37 possible applications for the C15 engine. But here are some of the main ones that they recommend:

  • Agricultural applications, such as for tractors and harvesters.
  • Bore or drilling.
  • Construction, such as chippers or grinders and cranes.
  • Mining.
  • Earthmoving equipment.
  • Trenchers.

There are plenty more applications, and you can check them on their website. If you’re looking for an agricultural tractor, the C15 is used in the Cat Challenger MT800C and MT900C series tractors.

If you’re seriously considering the C15 for your industrial needs, let’s take a look at some of its common problems before you decide:

CAT C15 Common Problems

The C15 has two main variations, the original one with a single-turbo, and the ACERT with its two-turbo setup. The original one was a lot simpler since it had fewer electronics. But it’s not without its problems:

Cat C15

CAT C15 Problems

The C15 is the successor to the older 3406E engine. One of the upgrades they made was relief slots on the cylinder head. This helps to prevent pressure on the gaskets, but unfortunately, the gaskets were still prone to failure.

If they fail, you have no choice but to replace them. Make sure you use OEM-spec gaskets when replacing them. A C15 gasket set will cost between $380 – $475 to buy on average. However, labor costs will make it substantially more expensive.

For cars, the labor cost to replace a head gasket is usually between $900 – $1,200. But for an industrial engine like this, you can expect it cost upwards of $3,000 for the labor cost alone.

Aside from that, the engine is mostly reliable. We recommend staying away from the MBN “Bridge” engine. They have more electronics which makes them more prone to developing problems. Additionally, they make less power and are said to use more fuel. If you see a C15 on sale with the MBN serial number, avoid it like the plague.

CAT C15 ACERT Problems

As mentioned, the ACERT engine has two turbos. This helps the engine to meet emissions standards at the time and allows it to have a maximum output of 590 horsepower. However, it does make the engine more complicated as a whole. Later models seem to be reliable, but earlier ones do have quite a lot of reliability issues.

Its rocker studs were a common problem in earlier models and were prone to breaking. Other problems include the exhaust manifold and its studs as well. Replacing the manifold will cost you around $1,600 for a complete set, but that doesn’t include labor costs.

If you’re going to buy the engine secondhand, then be wary of the fuel injectors. They’re known to fail over time, although there’s no exact information on how long they will last.

Oftentimes injectors will last around 100,000 miles, that’s around 1,500 hours in tractor terms. A set of replacement fuel injectors for the C15 ACERT will set you back anywhere between $250 – $400.

How Much Does The C15 Cost?

If you’re buying used, then the original C15 will set you back between $10,000 – $12,000 on average. Meanwhile, a rebuilt engine is usually around $14,000 – $16,000. As for new engines, we can’t get an exact quote as Caterpillar doesn’t list the price on their website.

As with any B2B (Business-to-Business) company, you’ll often have to inquire to get a quote. This is so that they can give you a more accurate quote depending on where you live, timeframe, and application.


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However, looking at remanufactured versions, they cost between $25,000 – $35,000. You can expect a brand new one to be in the same ballpark. Keep in mind this is just for the engine and does not include installation costs which will vary depending on your needs.

Meanwhile, the C15 ACERT usually costs about the same as used C15s. However, rebuilt ACERTs will cost upwards of $19,000. As for the new ones, expect them to cost upwards of $35,000.

Is The ACERT Variant Better?

This is the part where you need to talk with a Caterpillar sales team. Since these engines have multiple applications, you’ll need to inquire with them to find out which version would fit your needs.

If you want our advice, we lean towards the original C15. Mainly because it’s simpler and more reliable, not to mention slightly cheaper in the secondhand market.

We’ve also seen cases where owners of the ACERT engines removed one turbo, making it a single turbo just like the original C15. Partly because many owners feel the single-turbo setup has better power delivery. But mainly because it’s less complex and will make future repairs easier.

Additionally, it’s cheaper to convert the setup, rather than replace the two turbos when you need to. We don’t know about you but buying a twin-turbo engine only to remove one of them, effectively making them like the original single-turbo engine, kind of beats the point, no?

All of this is part of the reason why the original C15 was so successful and popular in the truck industry. When the engine first came along, it was also a popular engine option in trucks. Mainly Peterbilt and Kenworth trucks were using the C15.

However, since Caterpillar stopped upgrading the C15 in 2010, it has since fallen out of popularity with truck makers. But truckers – mainly owner-operators and small companies – still loved the engine, and it was a popular engine for glider kits. This brings us to:

CAT C15 In Glider Trucks

Glider kits refer to trucks that roll out of the factory without a powertrain and driveline. So, they “glide” out of the factory with just the chassis, the cab, and everything but the powertrain. Glider kits can either be new trucks or older trucks that have been repaired and restored.

The customer can purchase these glider kits, and then fit them in their engine of choice. Many glider kit companies, such as Fitzgerald, will have several engines for the customers to choose from. And if you guessed the CAT C15 is one of the most popular engines, then you’re right.

Even though production stopped in 2010, rebuild kits of the C15 were popular for gliders. Since Caterpillar and other truck part companies still supply replacement parts, the C15 remained a favorite. Especially the original C15 since it was more reliable.

Glider kits have been around for 50 years, with Fitzgerald being the industry leader. It became incredibly popular in 2010, with sales rising from just a few hundred a year to upwards of 10,000 units as recently as 2017.

It became so popular in fact that truck makers such as Peterbilt, Kenworth, Mack, and even Volvo also started offering glider kits alongside their ready-made trucks.

The reason behind its popularity is that glider kits are often cheaper. Usually around 25% cheaper than the MSRP of new trucks. This makes them very popular with owner-operators and small truck companies who don’t have a lot of capital to start or maintain their business.

Is It A Good Truck Engine?

It’s excellent, in fact. Many often regard it as the best truck engine ever made. While that’s up for debate, the C15 is certainly one of the best truck engines. Reviews of C15-equipped trucks note that it starts in the cold with no problem, and the immense torque can haul well over 45 tonnes of goods.

It’s probably not the most efficient engine when driven hard. Some note that highway runs with the C15 use around 5.2mpg, which is less than the average of 6.5mpg in modern trucks. Doesn’t sound like much, but in the trucking business, saving fuel is of utmost importance.

Another important aspect is, of course, reliability. The less time you spend in the workshop, the more time you can spend on the road making money. As mentioned, the C15 is a very reliable engine.

Service intervals are at 500 hours, and the simple design of the original C15 makes it less prone to electronic issues and therefore more reliable. Hence why the ACERT variant is less popular among truckers.

While the ACERT is plenty capable, the worse reliability means truckers tend to avoid it. They want to be on the road, not in a shop dealing with all sorts of engine electronics. This is why they often convert the turbo setup, as well as remove features such as the Diesel Particulate Filter.

Why The CAT C15 Is Dying

If you’re thinking of equipping your truck with a C15, you’re out of luck. When we say it’s dying, we mean its application as a truck engine is dying. Why? It all has to do with emissions. Here’s the story:

Caterpillar drew out of the truck engine business in 2010. Since then, they focus on making engines for off-highway use, and they no longer supply engines for new trucks. Most American trucks since then use either a Mack, Detroit Diesel, and now more often than not, a PACCAR engine.

The reason behind this was increasingly strict emissions regulations from the Environmental Protection Agency (EPA). Since the new law in 2007, Caterpillar decided that it was too costly to keep developing engines to keep up with the demands of the regulations. So, they focus on off-highway applications instead since the regulations are more lenient.

However, the C15 was still road-worthy. Since it’s cheaper, reliable, and still relatively efficient, it’s still a popular choice amongst truck owners and companies.

As mentioned, buyers of glider trucks love this engine even to this day. This keeps the engine alive on the road, even though Caterpillar drew out of the business well over a decade ago.

A New Emissions Regulation

It’s quite romantic, no? As petrolheads, we can relate to how much we can love an engine. Whether it’s because of reliability, performance, or simply the way it feels, sometimes we can’t help but fall in love with an engine. And it’s nice to see a great engine to get a second wind in life.

However, the C15 is meeting its demise. At least, on the road. In 2016, the EPA was planning to introduce a new law that has even stricter emission limits for trucks, especially class-eight trucks.

The new and stricter laws meant that trucks running an older engine – such as the C15 – won’t be able to operate. Since the engine is quite old, it produces NOx gases above the new limit. This also meant the demise of the glider business.

The law doesn’t actually outlaw the manufacturing of glider kits themselves. But since glider kits mostly use older engines that won’t meet the new limits, it effectively crippled the industry. Leaving owner-operators alike angry and without an option for more affordable trucks.

They did try to cap the production of glider kits to just 300 units per year per manufacturer in 2018 as part of their Phase II in introducing the new regulation. However, the law was not enforced due to backlash and pushback from the industry, including from Fitzgerald.

Alas, the new regulation came into full effect in mid-2021. The industry knew this was coming, and Peterbilt and Kenworth stopped making gliders in 2019. While the industry leader, Fitzgerald, diversified their business to stay afloat. They now focus on repairs, modifications, and act as a dealer for Peterbilt.

How This Affects Truck Operators

Owner-operators and small truck companies with smaller capital now only have two choices: either they buy a brand new truck. Or they buy a secondhand truck with an engine that meets the regulations.

Running trucks with an older engine such as the C15 will likely get them into legal trouble. While emissions testing will vary between states, there are around 28 states that require truck owners to do an emissions test at least once every two years.

Cat C15

If the truck fails an emissions test, then it can’t legally operate in that state. Changes will have to be made, such as repairing the engine (if it has an issue that affects emissions). Or an all-new engine that meets the requirements will have to be fitted.

Otherwise, the government will send a notice and require drivers to pay a fine. Violators are subject to civil penalties of up to $45,268, which is no small amount of money. That’s nearly $10,000 more than what the average truck driver spends on fuel annually.

While technically not the end, it seems that glider trucks are as good as dead. Technically, if the glider truck uses an engine that meets the new regulations, it will still be legal. However, since newer engines are more expensive, it offsets the cost benefits of buying a glider rather than a new truck.

The Argument For Glider Trucks

Hold on, don’t hate on the EPA just yet. The EPA’s argument is quite sound; they argue that 10,000 gliders produce emissions equal to 200,000 new trucks. Of course, this is a somewhat rough estimate and doesn’t account for whether these gliders travel as much as new trucks.

However, it can’t be denied that medium and heavy-duty trucks account for around 23% of greenhouse gas emissions from transportation in the US. While passenger cars and light trucks still contribute more, medium and heavy-duty trucks only make up about 8% of total vehicles on the road.

Cat C15

While it’s imperative that we reduce our carbon emissions for a better future, there is an argument to be made for glider trucks. For one, glider trucks are a form of recycling.

Not only you’re using an old engine that would otherwise turn to waste. Glider trucks often use a remanufactured old chassis, so you’re recycling a chassis that would otherwise be left to rust.

Fitzgerald claims that it saves around 12 million pounds of steel every year since you don’t have to produce the steel to make new trucks. Considering how steel production contributes to around 6.5% of CO2 emissions, that’s a point for the glider truck industry.

Of course, there are the economic benefits as well. It provides jobs, and it helps small companies and owner-operators to save money and grow their business. But that’s an entirely different conversation.

Can I Still Use The C15?

For off-highway use, yes. This includes using the C15 as a generator, or as a power source for machines like cranes, drills, mining equipment, and even agricultural vehicles.

Non-road or off-highway vehicles are not affected by the new regulation from EPA. They still need to conform to the Tier 4 EPA standards, which the C15 does meet.

So, if the C15 seems to meet your industrial engine needs, you can still use it. As long as it’s for off-highway use. We recommend inquiring further with a Caterpillar dealer to make sure the C15 will meet your needs.

C15 vs C18 Industrial Engines: Facts You Need to Know for Your Generator

  1. CAT engines are known for their reliability and long-lasting machines in various applications.
  2. The C15 and C18 engines are two CAT industrial engine models known for their excellent track record.
  3. Both engines were designed for similar applications, with comparable overall functionality and appearance.
  4. The C18 engine offers a slightly higher power capability than the C15, with a minimum of 575 HP and a maximum of 800 HP.
  5. The C15 engine offers a minimum of 475 HP and a maximum of 580 HP.
  6. Both the C15 and C18 engines meet the EPA Tier 4 standards for emissions.
  7. The C18 engine has significantly higher torque than the C15, with 2696 lb-ft at 1400 rotations per minute.
  8. The C15 engine offers 1958 lb-feet at 1400 rotations per minute.
  9. The C18 engine weighs more than the C15 engine, with a weight of 3688 lbs compared to the C15’s 3673 lbs.
  10. When shopping for a backup generator system, it’s essential to consider the size and specifications of the engine to choose the right one for your needs.

CAT C15: Wrap Up

The sad demise of the CAT C15 on the road aside, it’s still widely available for off-highway use. The CAT C15 is reliable, powerful, and replacement parts are also plenty so you don’t have to worry about your machine sitting dormant for too long while waiting for replacement parts.

If you’re looking for an industrial engine with marine applications, check out the 3208 Caterpillar engine. It can be used for agricultural machines, but can also be used for yachts, container ships, and other marine applications.

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