The Engineering Explained crew breaks down the finer points of engine braking, and why it's mostly okay.
Engineering Explained is back with another is it bad video, this time talking about the wonderful world of engine braking. This is actually a good topic to cover, as there is often conflicting information and opinions about this, even among those with a good amount of knowledge over and above the average car fan. The short answer is no, engine braking won’t hurt the car or its mechanical bits in the least, and can in fact provide some benefits. As with most things, however, there’s a bit more to it than that.
To start with, the video explains what engine braking is. The basic definition is simply lifting off the gas and letting the engine slow the car, which can not only save wear on the brakes, but also help average fuel mileage since fuel-injected cars cut fuel when the throttle is fully closed. The concern is whether or not that creates extra wear on the clutch, driveline, and transmission components, especially if you downshift. Depending on who you talk to, that can be a significant factor.
For example, a high-rpm downshift for engine braking can potentially increase wear on the gear synchronizers and shock the entire drivetrain, which could lead to broken parts. There’s also the issue of clutch wear, especially when slipping the clutch at high revs to engage the shorter gear. The argument here is that it’s far cheaper to replace brakes than a clutch or transmission parts, so why engine brake?
Engineering Explained takes the pro-engine braking standpoint that no harm is done provided you’re not doing something stupid like downshifting to a gear that will cause the engine to bounce off the limiter. However, a commenter on the video named oellinas pointed out that helical-cut gears in modern transmissions are designed to take a load when accelerating, but not necessarily when decelerating. The takeaway there would be that, if you frequently engine brake from higher rpm, even if you rev match and execute clean shifts, the increased reverse load on the gears alone could cause problems.
There’s plenty of coulda woulda shoulda at work here, but the general consensus is that, if you just take your foot off the gas while driving in a normal rpm range, there’s nothing wrong with letting the engine help slow you down. As for the rest, watch the video and check out the comments, then tell us your opinion on the matter.