CAT C15 Twin Turbo Problems: Symptoms, Reasons, and Fixes

The CAT C15 ACERT is an industrial engine from Caterpillar. The CAT C15 is commonly referred to as "CAT C15 Twin Turbo", however, this is a misnomer. The CAT C15 ACERT has two turbochargers. Yet, they are not the same, negating their description as a "twin turbo." Instead, what you have with the CAT C15 ACERT is two turbo engines with a high-pressure turbocharger and a low-pressure one. These turbos work together to remove turbo lag.

While this dual or "twin" turbo design is advantageous for reducing turbo lag, it comes with its own set of problems. Since there are more moving parts with the CAT C15 ACERT, it comes with some unique challenges when compared with other engine designs. We discuss three major CAT C15 ACERT problems.

CAT C15 ACERT Background

Despite the common usage of the term CAT C15 Twin Turbo, we will be using the correct name of this engine (CAT C15 ACERT) throughout the rest of this article.

While there were CAT C15 ACERTs between 1998 and 2002, The true CAT C15 ACERTs were released between 2003 and 2010. The distinguishing feature between the ACERT and non-ACERT C15s was that the ACERT models comply with the US Environmental Protection Agencies 2004 and 2007 emission standards. ACERT stands for Advanced Combustion Emissions Reduction Technology. There are a few CAT C15 ACERT models, they include:

• BXS (2003 -2004)
• MXS, NXS, RKS (2004 - 2006)
• SDP (2007 - 2010)

Generally, the CAT C15 ACERT is an engine used in industrial and agricultural applications. You will find the C15 ACERT in loaders, tractors, bore rigs, aircraft ground support tools, and more.

The C15 ACERT has an inline 6, 4-stroke cycle diesel engine with a 137 mm bore and 171 mm stroke. It uses a common rail direct injection fuel system. The maximum power of the C15 ACERT engine is 595 horsepower, and the minimum is 440 horsepower. Its rated speed is between 1800 and 2100 Revolutions Per Minute (rpm).

The twin-turbo nomenclature of the C15 ACERT is because of its turbocharger design. The turbocharger is a two-stage, variable geometry. The primary or high-pressure turbo generates higher boost pressures at lower engine speeds, including when idling, providing solid low-end torque. The secondary or low-pressure turbocharger works best at higher speeds, closer to the engine's top rpm, helping the engine produce more power at higher speeds with low particulate matter output.

CAT C15 ACERT Problems

All engines have problems. Some of these problems show up across different types of engines; others are unique. The CAT C15 ACERT certainly has its fair share of problems. These problems are identified here.

1) Emission Control System Issues

One of the main problems with the CAT C15 ACERT revolves around its emissions system. CAT C15 and C13 ACERT engines have been the subject of many lawsuits in the USA. Most lawsuits against Caterpillar and its C15 and C13 ACERT engines were about their emissions systems. The specific models were those released between 2007 and 2010. The C15 ACERT engine emissions system is considered defective by many operators and fleet managers.

Reasons

Caterpillar created the ACERT engines to comply with EPA requirements to reduce Particulate matter and Nitrogen Oxides (NOx) to very low levels. The dual turbo design was one way CAT was able to reduce particulate matter in the heavy-duty C13 and C15 ACERT engines. However, this solution increased NOx.

To reduce NOx, Caterpillar came up with an Intake Valve Actuator (IVA) system. It opens the intake valve longer than the camshaft would, forcing some of the combustion air out of the cylinder before ignition occurs. This way, there is a reduction in oxygen, nitrogen, and pressure during combustion. However, the IVA system was problematic because its timing was not consistent, and the wiring regularly failed.

Pre-2007 C15 ACERT engines already had issues, but it got worse with the 2007 - 2010 models when the EPA wanted even lower NOx and particulate matter emissions. So, CAT added new components like the Diesel Particulate Filter (DPF) to the C15 and C13 ACERT engines. The DPF catches soot and ash from the exhaust. However, with usage, the DPF will get clogged and start to affect engine performance. This is where the aftertreatment regeneration device (ARD) comes in.

ARD's primary function is to burn up the soot in the DPF. ARD, DPF, and Engine Control Module (ECM) are the significant parts of the regeneration system in the CAT C15. Most complaints make it clear that the C15 and C13 regeneration systems led to inconsistent performance in every operating condition despite repairs and replacements.

ARD regularly failed, which invariably led to DPF failure. The ARD and DPF replacements can be expensive. When they fail, the ECM releases error codes, which may shut down the engine. These codes cannot be cleared by users. They needed to be cleared with dealer passwords. This problem is costly, financially and time-wise. Also, these problems tended to recur.

The recurrent problems with these engine regeneration systems not only affected work performance but also led to a drop in the performance of the CAT C15 ACERT engines. Some other reasons for failed fuel burner regeneration in the C13 and C15 ACERTs include clogged injectors, fuel line issues, and sensor malfunctions.

Symptoms

Unfortunately, the main symptom of this problem is engine shutdown. Due to failed regeneration, the ECM may shut down your C15 ACERT engine, halting work.

Fixing

The solution to this emission problem involves repairing or replacing the affected components of the emissions system. However, many users have made it clear that this solution is temporary, and the issue is likely to reoccur because the problem is a core defect of the 2007 - 2010 ACERT engines.

2) Turbocharger Failure

The two-turbo design of the C15 improves performance and emissions compared to a single-turbo design. Nevertheless, these turbochargers are known to fail.

Reason

Some of the C15 models (BXS, MSX, NXS) use journal bearings with brass bushings. The C15 ACERTs Journal bearings use a rotating turbine shaft for its housing. There is a thin layer of oil between the shaft and the brass bushing of the bearing to reduce friction and increase smooth operation.

If there is significant debris or soot in the oil, the contact patch will lose its durability due to increased friction. In such a case, the journal bearings bushing may not rotate freely, leading the turbocharger to self-implode. The high-pressure turbocharger is more likely to become damaged first due to its faster rotation and smaller size.

Some other causes of turbocharger problems with the CAT C15 ACERT engine include loose carbon or debris in the engine, damaged fins, and air leaks.

Symptoms

Symptoms of turbocharger failure or implosion in the CAT C15 ACERT include:

• Oil loss in the turbocharger
• Low engine power.

Fixes

If one of your CAT C15 ACERT turbochargers has suffered damage, you have to replace it so far as the other one is not compromised. In case both turbochargers have failed, you must replace them both.

The newer SDP CAT C15 ACERT uses ball-bearing turbos instead of joint bearings. Ball bearings are more solid. Although, if you need a replacement, they are significantly more expensive.

3) Cylinder Head Problems

The cylinder head is on top of the engine block. Inside it are the intake and exhaust valves, valve seats, and valve guides. Also, the cylinder head is where you will find gaskets, coolant passages, fuel injectors, and the combustion chamber. It is vital for the following reasons:

• Seals the combustion chamber
• Controls air and fuel flow
• Moves heat away from the combustion chamber
• Supports the valve

Without a doubt, a problem here can be catastrophic. Unfortunately, the cylinder head is one of the parts of the C15 ACERT engine known to develop faults.

Reasons

A major source of cylinder head problems is overheating. Overheating will prevent the engine from maintaining safe operating temperatures. Excess heat will also cause cracks in the cylinder. Cracks may lead to loss of oil and fuel in the engine.

Besides overheating, failure of any of the components in the cylinder head can cause problems. Over time, the elements in the cylinder head may wear out. Head gasket failure and valve issues can damage the cylinder head of the C15 ACERT. Also, physical damage from a collision can damage the cylinder head as well.

Symptoms

Symptoms of cylinder head malfunction on the CAT C15 ACERT engine include:

• Loss of coolant
• High oil consumption
• Compression in the coolant
• Compression leak
• Excessive white smoke
• Overheating

Fixes

Depending on the particular issue, a cylinder head may be repairable. Small cracks can be welded shut, and warpage can be machined flat. However, significant damage to the head gasket will require a replacement.

It is not all the time a replacement will solve a CAT C15 ACERT head cylinder problem. It might be one of the defective components, like the gasket or valves, that need repair or replacement.

Conclusion

While the CAT C15 ACERT is a popular engine, especially with fleet operators, they have some well-discussed problems. This article identifies three major problems. But first we gave a brief background to this engine and why it is referred to as a "Twin Turbo."

The first problem revolves around the 2007 - 2010 models' emission systems. It has even attracted numerous lawsuits against Caterpillar. The other two problems discussed were turbocharger failure and head cylinder problems. It is essential to identify these issues to help would-be buyers and renters make a clear decision.