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Sinister Diesel CAT Duramax Fuel Filter

Rebuilding the 2001 to 2010 Duramax fuel filter head.

The fuel filter and filter head on 2001 to 2010 Chevrolet Silverado 2500HD and 3500HD trucks, along with 2001 to 2010 GMC Sierra 2500HD and 3500HD, equipped with the Duramax diesel V-8 engine becomes a point of frustration for all owners at some point. Because the trucks aren't fitted with any sort of lift pump (which helps move fuel from the tank to the high-pressure injection pump), the filter head features a built-in primer module. This primer is used to pull fuel up to the fuel filter in the event that the filter is changed or the system unexpectedly loses prime. Under normal circumstances this setup works perfectly adequately. However, as the trucks age the O-rings inside the filter head become worn and eventually leak.

A leak is bad for two reasons. First, fuel can escape leaving a mess to clean up (thankfully, the risk of fire from a diesel fuel leak is relatively low). Second, and the worse of the two, is that the filter head can suck air into the fuel system, which causes a whole host of issues from a no-start condition to high-pressure injection pump (CP3) failure. Fortunately, rebuilding the filter head is relatively easy, and the parts are inexpensive.

At the same time, we decided it would be prudent to also install a CAT fuel filter and adapter from Sinister Diesel. The benefit of the CAT fuel filter is simple: better filtration. While the factory filter is good for particles between 5 and 10 microns (depending on who you ask), the CAT unit filters down to 2 microns. The CAT filter also works as a water trap, though it doesn't have a drain or sensor as the factory filter does.

The whole process of rebuilding the filter head takes about two hours from start to finish. If you're just installing the Sinister CAT fuel filter adapter, the job takes about 10 minutes. The rebuild kit is about $25 from Merchant Automotive, while the Sinister CAT filter adapter will set you back about $150.

The fuel filter on 2001 to 2016 Duramax engine is found attached to the passenger side valve cover toward the rear of the engine. It can be hard to spot with the engine fully dressed, but the primer button on the top is a dead giveaway of what you're looking at (along with the big white filter hanging off the bottom). Engines built from 2001 to 2010 used the same filter housing; slight changes were made to 2011 to 2016 models, and 2017 to current. However, they all function the same in principle.

When we bought our project, a 2002 Chevrolet Silverado 2500HD, the engine was in pieces. So, we found most of the accessory pieces in the back seat, including the filter head. Also, because our truck was originally a "California" LB7, meaning it has exhaust gas recirculation (EGR) and a vacuum pump, our filter head played host to a bunch of sensors and vacuum hoses.

To clean things up a bit, we removed and relocated all of the extra sensors and hoses. The one wire left on the filter housing goes to the fuel heating element that is located inside the unit.

For rebuilding our filter head, we headed over to Merchant Automotive and picked up the company's O-ring kit for 2001 to 2010 engines. The kit includes everything needed to reseal the filter head, including the primer pump.

Disassembly and reassembly of the filter head are quite easy. The primer housing is removed with three screws, and the heating element is held in with two. Once apart, replace the O-rings and reassemble. Merchant Automotive has a great video on its website (and YouTube) that shows this in detail.

While we were working on the filter head, we also replaced the next most problem-prone part, the bleeder screw. From the factory this screw is made of plastic. After years of use it can become brittle and strip. We replaced it with an aluminum screw from Merchant Automotive.

The Sinister Diesel CAT fuel filter adapter kit is pretty simple. It utilizes a billet aluminum adapter, which is made right here in the United States, to adapt the threads from the factory AC Delco filter to those of the CAT filter. Because the kit is good for 2001 to 2016 trucks, it also comes with a spacer and longer bolts that push the filter head off the cylinder head for better clearance for 2011 to 2016 trucks.

Reinstalling the filter head starts by bolting the mounting bracket to the valve cover. You likely had to remove yours to perform the rebuild, so this part is review (unless yours came in a bucket in the cab, like ours did).

Next, the filter head can be bolted to the bracket. To make things easier, we spun the new Sinister Diesel CAT fuel filter adapter onto the filter head prior to installing it in the truck. When installing the adapter, a little bit of fuel on the O-ring will help keep it from binding.

The CAT filter adapter comes anodized in Sinister's trademark blue color, which adds a decent pop of flair to the engine bay.

We finished off the fuel filter housing rebuild by also replacing all of the fuel feed hoses to and from the housing. Pay no attention to the road grime on the filter—we're still running no inner fender covers.

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