Engine Braking Pros and Cons

[USNvet]

My old Audi would engine brake and use the rear brakes to modulate downhill speed when cruise control was turned on.

Engine braking is perfectly safe and fine IF you have a big enough engine to actually engine brake with. I used to have a Chevy Cruze with a 1.4 L 4-cyl. That engine was NOT big enough to effectively engine brake with. Wonder is the Jeep 2.0 has enough rotating mass to brake with.

Might have to take vehicle weight into account, too, as long ago a buddy had a gutless 36hp VW bug that would almost come to a stop when he let up on the gas. My 4xe with the regen button pushed reminds me of it!

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[Thrashie]

oh, my ram 2500 has a button for that, and it sounds awesome too!

 

[T.Pigott]

You've obviously never heard of Donner Pass or Wolf Creek Pass or Vail Pass. There are plenty of long, winding downgrades in the US. Mostly in the Rockies, but can also be found in the Owyhees in Oregon, the Blue Ridge Mountains as well as the Appalachians (specifically W. Va. and PA) and the Catskills in New York.

To OP, there is nothing wrong with using your engine as a brake or retarder to control speed. Truckers do it all day every day. I drove a manual car for 6 years and never had any engine troubles due to downshifting engine braking. The only way you're going to hurt anything in the drivetrain is by letting your RPMs get too high. Avoid that and you're golden.

I lived in Vail for 6 years. Also lived in LA Veta, CO for 3. Had lots of experience with the I-70 corridor between Vail and Denver and Cuchara Pass, LA Veta pass, ect. I had a 85 Nissan Sentra 5 speed. On the downhill slopes I let the transmission hold the car's speed steady in whatever gear worked but used the brakes for slowing down. But, on ice I always used the transmission. The brakes would lock the tires immediately on ice. After 10 years driving out there I just developed the habit of gearing down to a stop. Probably pisses off the people behind me here in GA. No brake lights when you gear down.

 

[Skrumpcious]

This is something that I looked into long ago when I owned a car with a standard transmission. The anecdote that was given to me by a mechanic was, "your transmission will get worn slightly (I think he said in the opposite side of normal wear) and just like doctors say with certain medical conditions, it (your transmission) will die with it, but not because of it."

I'm no mechanic and know very little about cars, but that sounded right and it eased my concerns about downshifting to brake.

 

[wcjeep]

Couple of us were towing to Moab. One person used zero compression braking coming down a mountain pass. His brakes liquefied. It was scary when it happened. Expensive to repair/replace brake components.

Follow the book recommendations. Don't over Rev the engine. Compression braking on a gas engine means using less vehicle service brakes.

 

[autotragic]

On the JL[U] specifically, is the wear and tear on engine and transmission components of manually downshifting (an automatic) to in part--in collaboration with the foot brakes--slow down the vehicle not worth it? Would it be better--assuming this engine braking isn't done in excess--to sooner wear out the brakes and replace them (a relatively minimal service item) than spare the brakes and put more of the deceleration efforts on engine's compression and transmission's innards?

Certainly we're working against the forces of inertia here when accelerating a vehicle but should we normally--big hill, lots of weight, and need to control excess speed notwithstanding as a good reason to downshift--leave deceleration to the brakes?

Thoughts?

TIA

I'm just going to say that compression braking with a gas engine is very effective and won't hurt it at all. It's a big air pump after all. In fact one of the "PROS" of gas engines is their superior engine braking ability. The lack of natural engine braking is why big diesel trucks have to have "jake brakes". They are absolutely essential on hills to keep from smoking your service brakes. At least until your big fancy automatic transmission decides to downshift at the wrong time and then misses the gear and you go down big hill in neutral but I digress. (NOTE: I love my "Georgia Overdrive" as much as the next guy but this particular hill had a sharp curve at the bottom and was not the place for that)

As far as your transmission goes generally speaking transmission lubrication systems work better while you are in gear than coasting. This should be obvious but I guess not. This is why Wrangler transfer cases have a neutral position for use while being flat towed. To keep the transfer case/transmission from spinning while not in gear to prevent damage. That alone should tell you what you need to know about that.

 

[Gnomad]

I manually downshift while driving around suburbia…just to listen to the glorious sound of my Hemi!

 

[Heimkehr]

I manually downshift while driving around suburbia…just to listen to the glorious sound of my Hemi!

I remember the first time I did that with the then-new Suzuki, sans earplugs, figuring I'd hear some awesome combustion sounds.

Nope. 'Twas just the distinct aural signature of an air-cooled thumper that doesn't benefit from an accelerator pump [in the carb] during deceleration. IOW, lots of mechanical farting in the form of pops from the exhaust.

Not what I was hoping for.

 

[Ratbert]

Certainly we're working against the forces of inertia here when accelerating a vehicle but should we normally--big hill, lots of weight, and need to control excess speed notwithstanding as a good reason to downshift--leave deceleration to the brakes?

I'm thinking I didn't fully understand what you were saying here when I first replied. On my second read it looks like you're explicitly asking about normal braking. That is, when not doing the more extreme stuff like descending a large hill.

In that scenario (and with an automatic) I'd just use brakes. The only reason I'd manually downshift during normal stopping would be to hear the exhaust gurgle / pop (e.g. in my wife's Mercedes AMG GLC43 or in a 392).

 

[AndySpill]

I'd also like to throw out there, if it hasn't come up before, that reducing speed on hills while under cruise control on an automatic JL is effected with vehicle controlled downshifting....

...so there's that.

 

[NWJeepr]

There's a balance. Do you need to shift 8-7-6-5-4-3-2-1 for every stop light? Nope.

But there is really good sense in using gears to provide engine braking on long/steep grades and also reducing speed for the downslope.

The JL isn't a 105,500 lb truck but many of the same concepts can be applied for safety, and it becomes important when towing. Brakes are relatively cheap but you also don't want to smoke them. They should be cool and ready should you need to come to a hard stop.

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