I am under the impression the issue with engine braking is the extra stress on the valves, not so much the clutch.
I think I remember someone saying the exact same thing about incandescent bulbs
that just seems that way, because of … you know … survivor bias
. . . and use a toothbrush with firm bristles to do the best job of scraping plaque off.
It’s been decades since I’ve even seen a toothbrush with anything but soft bristles.
Also, do people still put raw steak on a black eye?
This. Even in an automatic trans, downshift for long descents, and don’t ride the brakes. The routine ups and downs of rolling terrain? Don’t bother.
Which valves would these be? And why?
You forgot changing the rotor and distributor cap. Be sure you time your engine afterwards.
The cylinder exhaust valves. I am sorry if that was not clear. Im sure there are quite a few ‘valves’ in the various systems on a modern engine, but the cylinder valves are a primary component of a gasoline engine.
My understanding is that engine braking puts stress on the valves. This makes sense to me. The transmission and clutch are part of the drive train and obviously involved too, but ultimately its cylinder compression doing the work.
I believe I first heard it on the old CarTalk radio program, with the speaker stating that brake pads are cheap and cylinder heads are very expensive, probably a very long time ago. A quick google search returns several results saying it should not be a concern.
No, that doesn’t make any sense. The valves are closed during compression, so the material doesn’t experience any strain. Now, the lifters and springs might get a tiny amount of exercise, but so what- they last for billions of cycles.
The clutch will definitely get some extra wear each time a downshift happens, but that’s probably negligible.
In engine braking, where is the heat deposited? It’s got to be somewhere.
(note: This is not meant as a snarky gotcha question. I don’t know the answer, either. But heat has to be deposited somewhere, and wherever that is, I would expect that there would also be wear).
Thought question:
What generates more heat? The combustion of air+fuel in a compressed cylinder, or just the compression of air alone in the same cylinder?
Maybe not routinely but I drive a manual in Minnesota winters and sometimes downshifting is safer than braking on slippery roads. Dumping momentum into your power train can slow you when there just isn’t enough friction with the road to do the job; the automobile equivalent of air brakes.
Pennsylvania used to have some absolutely brutal winters. During those times I would shift into a lower gear when descending some of the icy hills in the area. It definitely helps.
It’s been quite awhile since we’ve had a really bad winter.
My computer doesn’t even have an “off” button; the Power button is strictly for turning the computer on, and pushing it when it’s already on just does a reboot. Turning the computer off is done entirely through Windows Start menu’s Power options (though on rare occasions I’ve been locked up badly enough to have to yank the power cord).
Hmm. Here on the west side of the pond we have no wall switches. Everything unplugs. About a billion times a month.
Can’t have too much of a deleterious effect, otherwise the log trucks and other diesels in my neck of the woods wouldn’t use compression brakes. And prefereably not at 4 a.m.!
My 6 speed Allison transmission allows me to shift into a manual mode, and pick a gear. Has been most helpful coming down from Government Camp, 6% grade, while carrying a camper and towing a 7500# boat. Keeps me from having to ride the brakes, and haven’t seen any problems
in 80,000 miles.
Especially obnoxious were the more militant “Save The Earth” types who condemned eating meat as a decadent luxury, when we could feed so many more hungry people on this overcrowded planet if we all lived on beans and rice. In my more trollish moments I’d declare that I would kill and eat their children before giving up meat.
I forgot about the wall switches. Discovered those years ago while visiting London.
Oh quite possibly. However in my case I think it’s less dangerous than being 110 lbs overweight.
Every style of toothbrush comes in soft, medium and firm. I’m a medium guy.
Yeah, if valves experience significant additional wear under deceleration, then semis with Jake Brakes would just be eating valves on the regular, and they’re just not.
The heat generated (other than a minimal amount in the clutch surfaces) is in the work done to compress the air in the cylinder. So that heat is removed through the cooling circuit and out the exhaust.
It’s got to be the air+fuel compression. Leaving aside the complication of variable valve lift and timing, the compression ratio (and associated heating) will be the same, so I don’t see how adding fire could be anything less than more heat.