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How One Loose Nut Can Kill The Cummins 6.7 Diesel

Original Source: The Autopian

Internal combustion engines are the fussiest things. Properly built and maintained, some will run for hundreds of thousands of miles, perhaps millions, while rarely if ever letting their owners down. And yet, sometimes all it takes is for one little fastener or clip to fail, and you’ll see whole engine trashed in mere seconds. The Cummins 6.7-liter diesel is an engine that can apparently suffer from that very affliction.

The Cummins 6.7-liter engine is the turbodiesel star of the Ram 2500 and 3500 lineup. It’s currently the most powerful engine option for those trucks, offering up to 400 horsepower and 1,000 pound-feet of “clean diesel torque” according to Cummins. The engine has been available in the Ram pickups since 2007. It’s prized for its good fuel economy and reliability, and Cummins even says it can go 15,000 miles between oil changes. But it’s got one wacky flaw, and while it’s rare, you really should be watching out for it.

A Loose Nut Gets Sucked Into The Engine

The “grid heater” is a resistive heating element that sits in the intake of the Cummins 6.7-liter engine. Its role is to heat the incoming air to make it easier for the air-fuel mixture to ignite in the cylinders. It’s essentially doing the same job as a glow plug. However, instead of being installed on a one-per-cylinder basis, the grid heater is able to warm the intake air heading to all cylinders.The problem with the grid heater is actually quite simple. A metal stud passes through the body of the grid heater, carrying 12-volt power to the heating element, and is held in place with a nut. Unfortunately, under certain conditions, that stud can fail, or that nut can come loose. In that case, the metal object tends to fall through the intake and directly into one of the cylinders, usually cylinder #6. At this point, it will usually impact the valves, the piston, the head, and the cylinder walls in short order. It does a great deal of damage in the process, usually necessitating an engine rebuild.

Ram 6.7l Grid Heater Bolt Failure Explained 00 03 47
The stud and nut that carries power to the grid heater.
Studdo
The stud and nut, and busbar in turn, can carry over 200 amps when the grid heater is in operation.
Studdo2
12 volts is supplied to the grid heater via this connection, which passes through to the stud and nut on the other side.

Ram 6.7l Grid Heater Bolt Failure Explained 00 00 28 (1)

Ram 6.7l Grid Heater Bolt Failure Explained 00 00 26

Ram 6.7l Grid Heater Bolt Failure Explained 00 00 28 (2)
If the stud or nut fail, they can do immense damage if it falls off inside an engine.

But why does the stud and nut fail? This can happen for a number of reasons. For a start, the stud and nut can get very hot. They are right next to the heating element itself, and on top of this, they carry a great deal of electrical current. Furthermore, as the engine ages and the stud and nut get dirty or corroded, the electrical connection between them can become poorer, leading to more resistive heating of the connection. Between regular thermal cycles and engine vibration, it’s no surprise that this stud and nut come loose or occasionally even snap in the field. In extreme cases, if the solenoid controlling the grid heater fails, the heater can become stuck on, and the stud and nut can allegedly even melt off.

Diesel tuners Banks Power note that the problem was once thought to only affect Ram trucks in colder climates, where the grid heater was used to a higher degree. However, company notes it has since seen  the problem in engines from across the country, including those from warmer climates.

Thankfully, the problem can be caught early. Banks Power notes that a damaged grid heater stud and nut will not conduct electricity as well as it should. The high resistance of the connection can trigger check engine codes—either P2609 (Intake Air Heater System Performance) or P0542 (Intake Air Heater A Circuit High). This is a surefire clue that the grid heater should be physically checked.

The grid heater can also be checked manually. Getting to the stud itself involves removing the intake elbow, fuel lines and intake plate. It’s not a huge job, but not a small one either. However, an easier test can be done without disassembly. There’s a 12-volt lead that hooks up to a connection on the top side of the grid heater, which is directly connected to the stud itself. Wiggling that connection can give you a clue as to the state of the stud. If it moves easily or is excessively loose, it’s a strong suggestion that the stud has already suffered significant damage and could be broken or close to breaking. Indeed, Banks Power notes that in several cases, a damaged stud can be sheared simply by hand action. In these cases, the grid heater should be fully removed for checks and repairs prior to starting the vehicle. Else, there is a high chance of the engine ingesting a dropped nut or broken stud.

Ram 6.7l Grid Heater Bolt Failure Explained 00 00 44

Ram 6.7l Grid Heater Bolt Failure Explained 00 01 20
In some cases, Banks Power says minor agitation by hand is enough to break a compromised stud/nut assembly.
Ram 6.7l Grid Heater Bolt Failure Explained 00 00 46
Wiggling the 12-volt connection to the stud can be a good way to test whether the stud has become damaged.

Banks Power notes that no recall or service bulletin has ever been issued for the grid heater stud issue. Ram has recalled certain 2021-2023 model year trucks for issues with the relay that drives the grid hetaer, but not the grid heater itself, based on searches conducted by The Autopian.

So what is the fix? Well, if the grid heater stud is damaged, replacement is the obvious solution. However, given the original design is subject to failure, replacing with stock parts is not an ideal permanent fix.

Alternatively, you can look to the aftermarket. BD Diesel sells a number of kits that claim to solve the problem in different ways. You can delete the grid heater with a simple kit and intake mod, but you’ll lose the benefit it brings to cold starting performance. The company also notes that it can’t ship this to California, presumably for emissions reasons. It’ll also make your truck throw intake heater codes unless you get a tuner to code that out. Alternatively, you can buy an upgraded busbar kit. The thicker metal part has lower resistance to reduce heating, and it’s also designed with fasteners that can’t drop into the intake.

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