Exhaust or Jake Brake
Q: You recently updated a previous story regarding the catastrophic mechanical failure of a 6.6-liter Duramax diesel engine in a 2003 Chevy truck. One sentence caught my eye: "An exhaust brake, used to amplify engine braking on a diesel engine, does have the potential for producing excessive backpressure, which can cause valve float and lead to valve-to-piston contact." A few months ago, I purchased a new 2006 Ram 3500 SLT 4x4 with the Cummins ISB 5.9-liter I-6 coupled to Dodge's six-speed manual transmission. As part of the negotiations, I ordered it with the Jacobs exhaust brake as a Mopar dealer-installed option. I chose the Jake brake over other exhaust brakes because it comes with a comprehensive three-year/100,000-mile warranty. I'm pleased with the exhaust brake's performance, but after reading your article, I'm concerned about something like that happening to my new truck. Since Dodge, Cummins, and Jacobs collaborated on this exhaust brake, I'm hoping the risk of such damage is close to negligible compared with other manufacturers' units. Is that the case? Do you have any advice for usage of the Jacobs brake (specifically regarding to the general directions from Jacobs to keep the rpm as high as possible without exceeding 3200)?
A: Exhaust brakes have the potential to produce excessive backpressure, which can overpower exhaust-valve spring tension, cause valve float, and eventual valve-to-piston contact. But engine damage from a quality exhaust brake is by no means a common occurrence, especially when operated as directed by the manufacturer.
Our previous story involved a truck manufacturer implicating an aftermarket exhaust brake as the cause of engine damage in denial of a warranty claim, but there was no evidence available to support the allegation. An engineer's report, in conjunction with owner compensation from the truck manufacturer, supported the innocence of the exhaust brake in question.
Thumbs up on choosing the Jacobs exhaust brake, approved by Cummins and Dodge as a dealer-installed option. This should, if used correctly, eliminate the possibility of engine damage or discrepancies with related powertrain warranty claims. The magic number is 3200 rpm; let's call it the Jacobs redline. Exhaust brakes do their best work at higher engine speeds, but exceeding the 3200-rpm threshold during deceleration may produce dangerously high levels of backpressure, similar to how accelerating past your truck's redline exceeds the engine's designed capabilities, and therefore increases the risk of engine damage. Most exhaust brakes don't allow the butterfly to close all the way, or they incorporate a calibrated orifice to avoid a complete blockage of the exhaust system. This prevents backpressure from surpassing the engine's limitations--even if the exhaust brake fails and is stuck closed. But again, engine safety goes out the window if you blow by that Jacobs redline. An exhaust brake can be a valuable asset and a reliable component for commercial and light-duty diesel-truck applications.