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Frequently Asked Questions

Skyline Emissions

Who is Skyline Emissions?

Skyline Emissions is a subsidiary of ESW Group. Skyline Emissions’ mission is to build high quality, cost-effective aftermarket diesel particulate filters (DPFs) and diesel oxidation catalysts (DOCs). With a new state-of-the-art facility, Skyline is poised to meet the demand for aftermarket DPFs and DOCs. The Skyline video is a good introduction to what Skyline does.

ESW Group is a company with many years of experience in diesel engine emissions control and engine and vehicle testing.

Under the brand ESW Group, we produce retrofit emission control systems for on- and off-road diesel engines, with over 20,000 installations around North America. Our products are supported by knowledgeable and experienced engineering, service, and warranty teams.

The ESW America subsidiary conducts engine and vehicle performance and emission testing at its Montgomeryville, Pennsylvania facility, with eight test cells for engines and vehicles between 20 and 1000 hp (15 to 750 kW).

Please check out the ESW Corporate Video for more information.

Where can I buy a Skyline Diesel Particulate Filter (DPF), Diesel Oxidation CAtalyst (DOC),  Gasket, or clamp?

Skyline DPFs, DOCs, clamps, and gaskets are sold, installed and supported through a network of distributors across North America. Contact us to find the distributor in your area.

Skyline Advantages

Why should I choose a Skyline DPF product over others?

Skyline DPFs are designed to be direct replacements for parts from the original equipment manufacturer (OEM), with exact fit geometry. Using OEM-grade substrates and coatings, Skyline provides performance equivalent to the OEM part. In addition to complying with emissions regulations, the Skyline DPF has demonstrated passive regeneration performance 50% greater than some other aftermarket products. It is more efficient, it will last longer, and if properly maintained, you will experience fewer warning lights. Essentially, Skyline DPFs are designed to keep your truck in service.

How does the backpressure compare between the Skyline DPF and OEM DPF?

DPF backpressure is an important performance characteristic. High backpressure can increase fuel consumption and shorten the lifetime of the DPF. The Skyline DPF is designed to be an exact replacement to the OEM part, including backpressure. ESW has extensively tested the Skyline DPF in our emissions testing facilities and in the field to ensure that the backpressure performance is equivalent to the OEM product. You can be assured of OEM level performance on every Skyline DPF, as we use only established OEM suppliers for our DPF products.

Why should I choose a Skyline DOC product over others?

The DOC is a very important part of a vehicle’s aftertreatment system. Its catalytic coating provides the means to keep the DPF clean during normal operation and active regeneration events. The Skyline DOC is designed to be an exact replacement to the OEM part with particular focus on its catalytic activity. ESW has extensively tested the Skyline DOC in our emissions testing facilities and in the field to ensure that performance is equivalent to the OEM product. You can be assured of OEM level performance on every Skyline DOC, as we use only established OEM suppliers for our DOC products.

Product Coverage

What model year range do Skyline DPFs and DOCs cover?

Skyline DPFs and DOCs are available for a wide variety of 2007 and newer diesel engines. The complete listing is available on the website. To find a specific part, use the Skyline search tool.

Can I use a Skyline DPF or DOC in California?

No. Skyline products are not approved for sale, installation, or use in California. Violators could be cited by state vehicle inspectors.

How to Buy Skyline DPFs and DOCs

How do I find the Skyline parts I need?

The most direct way is to enter the OEM part number in the search field on the Skyline website to find the correct replacement Skyline DOC or DPF. Or, you can try searching by engine model or by browsing the collection. Contact a Skyline dealer if you need assistance.

Is there a minimum order?

Skyline has no minimum order rules, but your local distributor might. Contact us to find the distributor in your area.

Can I order online?

No. Skyline DPFs and DOCs are sold, installed, and supported through a network of specialized distributors across North America. Contact us to find the distributor in your area.

If you are interested in becoming a Skyline distributor, contact Skyline for more information.

Does Skyline sell replacement parts for retrofit DPF systems?

No, but its associated division ESW Group does. Visit the ESW Group website for more information about CARB-verified retrofit systems and parts.

Warranty On Skyline DPFs and DOCs

What is the warranty on my Skyline DPF or DOC?

Skyline DPFs and DOCs are backed by a 3 year, unlimited mileage warranty. Consult Skyline's terms and conditions for details.

Who do I contact about warranty questions?

Contact a Skyline distributor or consult your owner’s manual. If you still have questions that have not been answered, email us here.

How do I register my newly purchased Skyline DPF or DOC for Warranty?

No registration is necessary. Your proof of purchase – the receipt from the Skyline distributor -- is your warranty card. The start date for the warranty period is the date of purchase.

Maintenance for DPFs and DOCs

Why does my DPF require periodic maintenance?

Fuel and oil contain inorganic additives to help protect your engine and extend the life of the oil. During the combustion process, they are turned into ash, which collects in the DPF over time. Unlike the black carbon in the exhaust, which is removed during the regeneration process, the ash can only be removed by a cleaning device. This requires the DPF to be removed from the engine. The cleaning interval varies for each engine manufacturer (and sometimes between engines from the same manufacturer) and can be found in your vehicle’s service guidelines. You should follow the engine manufacturer’s recommended cleaning intervals for your Skyline DPF just like you would for the original DPF.

Note that the amount of ash is directly related to the amount of oil an engine consumes. High oil consumption or high hours of service means more ash in the DPF and may require more frequent cleaning.

How do you maintain a Skyline DPF?

The Skyline DPF is designed to be an exact replacement to the OEM part, so you maintain the Skyline DPF just like you maintain the OEM DPF. Refer to the OEM service documents for instructions and cautions.

Where can I get my DPF cleaned?

A network of DPF cleaning services has developed since DPFs became standard equipment on trucks and buses. Some Skyline distributors also have cleaning services, so your Skyline distributor would be a good starting point to find a reliable cleaning service.

My company has its own filter cleaning machine or a preferred service provider. Can I use it to clean my Skyline DPF?

If a filter cleaning machine is approved by the OEM, it can be used to clean your Skyline DPF.

Does a Skyline DOC require periodic maintenance?

No, unless DOC maintenance is specifically called out in your engine’s maintenance instructions.

DPF and DOC Technical Topics

Why do some of Skyline’s recent DPF releases look different than the earlier DPFs?

In recent years, some OEMs have started to use a different type of DPF material in their heavy-duty aftertreatment systems. Since Skyline matches the OEM design, our DPFs use the same type of filter material.

These DPFs are made from a material called Silicon Carbide (sometimes abbreviated as SiC, its chemical formula). It differs from the more common material (cordierite) in color and how the filter is assembled. Silicon carbide is dark gray and the DPF is almost always a collection of smaller pieces that are cemented together, often in a checkerboard pattern. In contrast, a cordierite DPF is typically tan and built as a single continuous cylinder. The photos below illustrate these differences.

Photographs of silicon carbide DPF and cordierite DPF

Unless the OEM specifies otherwise in their service documents, a cordierite filter must always be replaced by a cordierite filter, and a silicon carbide filter replaced by a silicon carbide filter. Although both DPF types provide nearly 100% PM reduction efficiency, the OEM’s regeneration strategy and fault codes are designed around a particular material, so switching material without OEM authorization could cause undesirable effects.

Why is maintaining an engine important?

A poorly maintained engine lowers your fuel economy, increases emissions, and shortens the life of your engine and emissions critical components such as the DPF and DOC. Deferred or neglected maintenance items may include the following: restricted air filters, stuck EGR valves, faulty fuel injectors, faulty turbochargers, and degraded charge air coolers.

Regular vehicle, engine and after-treatment maintenance (including the DPF), will yield more vehicle “up time,” with reduced operating costs, and maximize your return on the investment that you made in the vehicle.

What do Passive Regeneration and Active Regeneration mean?

As an engine runs, the DPF collects solid particles called particulate matter (“PM”) which consists of carbon, unburned fuel and oil, the ash from fuel and oil additives, as well as any other contaminants from the exhaust. Over time, the DPF will fill with PM. The process of removing the combustible part of the PM (the carbon, unburned fuel, and unburned oil) is generally called “regeneration.”

Under driving conditions with the engine producing high exhaust temperatures – on a highway or pulling a heavy load – the catalytic coatings on the DPF and DOC are sufficient to keep the DPF clean. This cleaning process that takes place without any activity by the engine is called “passive regeneration.”

When the exhaust temperature is not sufficiently high, the vehicle’s exhaust system relies on auxiliary fuel injection to raise the temperature of the DPF to a level at which the most of the PM is oxidized. This process is actively controlled by the engine‘s controller and therefore called “active regeneration.” The active regeneration occurs periodically and is not noticeable to the driver. Numerous sensors on the engine and exhaust system provide input to the engine‘s controller so it can trigger and control the process.

Most engines have another type of active regeneration that is initiated by the operator when the vehicle is standing still. This process is called "stationary regeneration" or "forced regeneration." During the process, the engine controller modifies the engine speed, intake air flow, EGR rate, and other functions to allow the DPF temperature to reach a suitable temperature. Consult your engine or vehicle owner's manual for details.

In most cases your vehicle relies on both passive and active regeneration to keep the DPF clean and the vehicle operating normally.

Why is it not good to idle the engine for long periods?

Extended periods of idling shorten the lifetime of your engine, consume fuel unnecessarily and load up the DPF . In addition, some states, private entities (like warehouses or loading docks), and many municipalities have strict anti-idling laws or policies.