Obsolete Advice (For things that still exist)

[Machine_Elf]

@Chronos

In engine braking, where is the heat deposited? It’s got to be somewhere.

Inspired by the engine braking discussion in this thread, I started a new thread to keep from totally hijacking things in this thread:

Engine braking

Inspired by a discussion on engine braking in this thread: While heat transfer is an inevitable part of engine braking, it’s possible to envision a hypothetical engine with no heat transfer at all that still provides engine braking. Consider an ordinary gasoline four-stroke engine. In the intake tract, there’s a movable throttle plate: open it wide, and the engine produces maximum torque, close it down to almost nothing and the engine breathes in just enough air (and fuel) to overcome fric…

I’m copy-pasting from that post the part that’s relevant to this thread, i.e. the advice (don’t use engine braking) that’s obsolete because of more knowledge and technology changes.

=======================================

=======================================

As far as temps go, well, for gasoline or diesel, it’s not running any hotter than it is when it’s idling, because it’s doing pretty much the same thing as far as squeezing/expanding the air in the cylinders. In fact, for the case of the diesel using a compression-release brake, temps are actually very cool during the expansion stroke. Likewise, the loads on the machinery aren’t particularly large, unless you’re spinning the engine at ludicrous speeds.

Is engine braking hard on the gears in your transmission/gearbox? Not particularly. The modest deceleration of engine braking is no harder on the gears than accelerating at the same rate. The faces of gear teeth are extremely hard and will probably be the last things to fail. More to the point, the “front” face of each gear tooth is what racks up the wear as you drive 100,000 miles in the forward direction; the “rear” faces of the teeth, the faces that get loaded during engine braking, will only see a tiny fraction of the miles that the “front” faces do.

Is engine braking hard on the clutch(es) in your transmission/gearbox? If you’re a skilled manual transmission enthusiast, then when you downshift, you can rev-match the engine before you let the clutch out, resulting in minimal clutch wear. For automatic transmissions before the advent of electronic throttle control, downshifting meant that clutch bands inside the transmission had to briefly slip to drag the engine up to speed during a downshift, and yes, that meant wear. For at least some late-model cars, that’s a thing of the past: when you request a downshift, the computers that are actually managing your drivetrain for you will blip the throttle to rev match, resulting in virtually zero wear on the clutch bands in the automatic transmission (or clutch plates in your dual-clutch transmission).