Engine braking opinions?
04-06-2022, 09:22 AM
#1
AudiWorld Member
Thread Starter
Engine braking opinions?
I live at 2100 ft. My commute consists of a long descent along a ridge, and then a drop down to sea level, a total of 8 miles. If I'm the only car on the road I can make the whole thing without touching the accelerator and hardly touching the brakes.
The issue is when I'm behind someone who feels the need to brake sharply before every slight curve in the road, or to go 15 mph below the speed limit. In that case I would like to paddle shift to a lower gear to avoid overheating my rotors and to save brake life.
What I'm concerned about is that for the whole 8 miles the oil temperature still hasn't warmed up enough to even register on the readout. So running the engine to high RPM even though it's not putting out power probably isn't ideal. On the other hand, modern low-viscosity oils are pretty good even at low temperature.
What's everyone's opinion, use the brakes and keep the engine RPM low until the oil actually warms up, or use engine braking and keep the brakes and rotors cooler?
The issue is when I'm behind someone who feels the need to brake sharply before every slight curve in the road, or to go 15 mph below the speed limit. In that case I would like to paddle shift to a lower gear to avoid overheating my rotors and to save brake life.
What I'm concerned about is that for the whole 8 miles the oil temperature still hasn't warmed up enough to even register on the readout. So running the engine to high RPM even though it's not putting out power probably isn't ideal. On the other hand, modern low-viscosity oils are pretty good even at low temperature.
What's everyone's opinion, use the brakes and keep the engine RPM low until the oil actually warms up, or use engine braking and keep the brakes and rotors cooler?
04-06-2022, 03:48 PM
#2
AudiWorld Senior Member
Use the brakes - they are a lot cheaper to replace than an engine or transmission are are intended to be replaced as needed. Don't have them on all the time but allow as much cooling as possible cooling time between brake presses. IMO a firm press with cooling periods is better than having brakes on gently for a longer period of time. This scenario is when I am glad that I have a manual transmission.
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Nakedhoof (04-08-2022)
04-06-2022, 04:08 PM
#3
AudiWorld Super User
Using engine braking when going downhill is generally a non-issue. I don't know why some people make it a problem. 25 years ago I learned driving with a manual transmission living in the Swiss alps and learned to downshift to the lowest possible gear so that the car would not gain or only slightly gain speed coming down from a mountain. That's how everybody drove with a manual transmission. Around that time some cars still had drum brakes which could overheat if you didn't use engine braking. My parents had a Mustang at one point with drum brakes and 4 speed automatic transmission. That car regularly overheated the brakes coming down from a mountain. With only 4 gears it was difficult to find a proper gear ratio to not have to use the brakes constantly. Nowadays with disc brakes this is less of an issue, but you can still overheat them or at a minimum glaze the pads from constantly riding them. Sure, brakes are cheap to replace, but if they fade driving down a mountain that's not very pleasant.
You bring up an interesting point, though. One difference since then is that modern cars have fuel injection and for emissions control they cut off the fuel supply when coasting, so there is no combustion taking place to get the engine to operating temperature. You are effectively dragging a cold engine down the mountain under the car's momentum. That's the worst kind of wear that you can get, because the metals haven't expanded yet. Not really sure what the answer here is, but I'd probably drive in a way to get the engine up to operating temperature, before using too much engine braking. On the other hand back in my home country people still live on mountains and drive down in the morning when the car is cold, and I haven't heard of engine damage being typical in such vehicles.
You bring up an interesting point, though. One difference since then is that modern cars have fuel injection and for emissions control they cut off the fuel supply when coasting, so there is no combustion taking place to get the engine to operating temperature. You are effectively dragging a cold engine down the mountain under the car's momentum. That's the worst kind of wear that you can get, because the metals haven't expanded yet. Not really sure what the answer here is, but I'd probably drive in a way to get the engine up to operating temperature, before using too much engine braking. On the other hand back in my home country people still live on mountains and drive down in the morning when the car is cold, and I haven't heard of engine damage being typical in such vehicles.
Last edited by superswiss; 04-06-2022 at 04:14 PM.
04-07-2022, 05:33 AM
#4
AudiWorld Super User
A combination of the two - in the corner scenario, just use the brakes, following down a plodder, use a lower gear. As the others mentioned, constant brake pressure best avoided to avoid overheating/fade. In terms of higher RPM, sure, avoid 4000rpm+ when cold. But the engine won't care whether you're at 1700rpm or 2500rpm.
And saving the cost of brake pad wear is likely to be offset by the additional fuel consumption from being in a lower gear, so I wouldn't get too concerned about that. Plus you're probably not using the brakes much going home 😁
And saving the cost of brake pad wear is likely to be offset by the additional fuel consumption from being in a lower gear, so I wouldn't get too concerned about that. Plus you're probably not using the brakes much going home 😁
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TT-S4 (04-14-2022)
04-07-2022, 10:04 AM
#5
AudiWorld Member
Thread Starter
A combination of the two - in the corner scenario, just use the brakes, following down a plodder, use a lower gear. As the others mentioned, constant brake pressure best avoided to avoid overheating/fade. In terms of higher RPM, sure, avoid 4000rpm+ when cold. But the engine won't care whether you're at 1700rpm or 2500rpm.
And saving the cost of brake pad wear is likely to be offset by the additional fuel consumption from being in a lower gear, so I wouldn't get too concerned about that. Plus you're probably not using the brakes much going home 😁
And saving the cost of brake pad wear is likely to be offset by the additional fuel consumption from being in a lower gear, so I wouldn't get too concerned about that. Plus you're probably not using the brakes much going home 😁
04-14-2022, 01:01 PM
#7
Some people are under a mistaken view that "engine braking" is somehow detrimental to an engine.
Based on understanding how an engine works, there is no greater stress, wear, or tear on an engine while "engine braking", then there would be when accelerating, or even keeping a steady rpm while cruising.
The engine works in the same way whether it is in positive power production, or when it is being spun by exterior mechanical forces, such as gravity when going down a hill.
The main differences are, when in positive power production the engine requires air, fuel, and spark in order to create power to move the vehicle.
When accelerating, that is when there is the most stress on the engine and other systems.
Starting a stationary object moving, requires the greatest amount of energy, and force/torque, and that creates the greatest stress on an engine, and associated drivetrain components.
In acceleration or steady speed conditions, the brake system is largely not under stress, as it is not being called upon to do its function.
In deceleration, the brake systems is being called upon greatly. The energy of the moving vehicle is transformed into friction, heat, as the brake pads contact the rotors, and the tires bite/friction onto the road surface.
If the trans is in neutral, the engine is under much less stress as it is not creating power, nor being called on to help control vehicle speed.
If we come to a downhill section, we no longer need to produce the force/power to accelerate, or to keep momentum. At the start of the downhill, gravity is the force acting on our cars.
Gravity is the force moving/pulling the vehicle down the hill.
We drivers need to maintain speed control as the force of gravity starts to accelerate our vehicle down that hill.
To control the speed we need, we need to control that force.
To do so we have some options.
Friction is one of our options. We can apply friction in a few different ways.
We can use our brakes, which applies great friction with the contact of brake pads to brake rotors.
Doing that creates a lot of heat, as we are now transferring the force of gravity into heat, by way of friction.
That brake force also transfers to the tire material to bite into the road surface, which creates another great friction point, and heat is generated there as well, as the force/energy of gravity is converted to heat.
All that helps to control descent speed.
What can we do to take some of the stress off of the brake system, to help us control the speed of our car, as we control the force of gravity?
We can engage the engine to help out.
"Engine braking", is engaging the engine's mechanical functions, but not using its power generating capabilities.
By putting the transmission into a gear and engaging the engine, we can now use the engine's mechanical functions to help control our car's speed.
By engaging the engine, for speed control, the engine becomes another tool by which to control descent speed.
Now we can use the brakes, tires, and engine to control the force of gravity, and thus our speed.
Engaging the engine to help control speeds divides all of the force of gravity, thus reducing the stress and strain on the brakes.
The tires are still having to provide their frictional control as they did even with just the brakes in use.
When going down a steep hill, if we were to disengage the transmission, and not use the brakes, the force of gravity continues to accelerate our cars, and that energy would easily overcome the tires frictional ability.
Adding in the brakes, provides a great amount of friction and control. Adding in some engine braking adds some more frictional control.
Using the brakes, engine braking, and tires, provides the maximum amount of control.
So, is engine braking useful?
Yes, it can be.
Does engine braking wear the engine more if it is used to control descent speed?
Yes, it will, but no more than accelerating our cars does.
There is a caveat with that.
If the descent is such that it would force the engine into extreme RPM, beyond its designed mechanical limits, then using engine braking can cause excessive strain on the engine and cause it to break.
What about the brakes?
If a descent were such that a car's brake system becomes so overtaxed, and there is extreme heat generated such that the brake components fail, then that system too can break.
Those are extremes, however.
Back to the main point. Is engine braking a good way to help control vehicle speed in a downhill descent?
Yes, it is.
By using the engine to help control speed, we now have greater levels, margins, of safety as we are engaging the engine, brakes, and tires.
Thus, we've spread the frictional load among three systems rather than just two.
Does engine braking really create that much stress so as to greatly increase wear and tear such that using engine braking will break the engine sooner rather than later?
The point really is, we have more than just the brake system and the tires to help us control descent speed, and do so safely for the health of the brake system, engine, and drivetrain.
Spreading the work means that each system takes on less stress, wear, and tear...well except for the tires.
If you ride the brakes to control speed, then you may overheat the brake parts, which leads to having to replace them sooner, not to mention the loss of braking power and control, which can result in having to replace your whole vehicle, and maybe a knee, elbow, or hip.
If you can engage your engine to help assist the brakes, then you're providing yourself better control of your vehicle as you spread the load.
A vehicles engine is capable of creating such force that it can overcome a heavy stationary object, and cause it to start moving and accelerate.
Using the engine to help control descent speed, and using your brakes as needed with that, is a good thing.
Based on understanding how an engine works, there is no greater stress, wear, or tear on an engine while "engine braking", then there would be when accelerating, or even keeping a steady rpm while cruising.
The engine works in the same way whether it is in positive power production, or when it is being spun by exterior mechanical forces, such as gravity when going down a hill.
The main differences are, when in positive power production the engine requires air, fuel, and spark in order to create power to move the vehicle.
When accelerating, that is when there is the most stress on the engine and other systems.
Starting a stationary object moving, requires the greatest amount of energy, and force/torque, and that creates the greatest stress on an engine, and associated drivetrain components.
In acceleration or steady speed conditions, the brake system is largely not under stress, as it is not being called upon to do its function.
In deceleration, the brake systems is being called upon greatly. The energy of the moving vehicle is transformed into friction, heat, as the brake pads contact the rotors, and the tires bite/friction onto the road surface.
If the trans is in neutral, the engine is under much less stress as it is not creating power, nor being called on to help control vehicle speed.
If we come to a downhill section, we no longer need to produce the force/power to accelerate, or to keep momentum. At the start of the downhill, gravity is the force acting on our cars.
Gravity is the force moving/pulling the vehicle down the hill.
We drivers need to maintain speed control as the force of gravity starts to accelerate our vehicle down that hill.
To control the speed we need, we need to control that force.
To do so we have some options.
Friction is one of our options. We can apply friction in a few different ways.
We can use our brakes, which applies great friction with the contact of brake pads to brake rotors.
Doing that creates a lot of heat, as we are now transferring the force of gravity into heat, by way of friction.
That brake force also transfers to the tire material to bite into the road surface, which creates another great friction point, and heat is generated there as well, as the force/energy of gravity is converted to heat.
All that helps to control descent speed.
What can we do to take some of the stress off of the brake system, to help us control the speed of our car, as we control the force of gravity?
We can engage the engine to help out.
"Engine braking", is engaging the engine's mechanical functions, but not using its power generating capabilities.
By putting the transmission into a gear and engaging the engine, we can now use the engine's mechanical functions to help control our car's speed.
By engaging the engine, for speed control, the engine becomes another tool by which to control descent speed.
Now we can use the brakes, tires, and engine to control the force of gravity, and thus our speed.
Engaging the engine to help control speeds divides all of the force of gravity, thus reducing the stress and strain on the brakes.
The tires are still having to provide their frictional control as they did even with just the brakes in use.
When going down a steep hill, if we were to disengage the transmission, and not use the brakes, the force of gravity continues to accelerate our cars, and that energy would easily overcome the tires frictional ability.
Adding in the brakes, provides a great amount of friction and control. Adding in some engine braking adds some more frictional control.
Using the brakes, engine braking, and tires, provides the maximum amount of control.
So, is engine braking useful?
Yes, it can be.
Does engine braking wear the engine more if it is used to control descent speed?
Yes, it will, but no more than accelerating our cars does.
There is a caveat with that.
If the descent is such that it would force the engine into extreme RPM, beyond its designed mechanical limits, then using engine braking can cause excessive strain on the engine and cause it to break.
What about the brakes?
If a descent were such that a car's brake system becomes so overtaxed, and there is extreme heat generated such that the brake components fail, then that system too can break.
Those are extremes, however.
Back to the main point. Is engine braking a good way to help control vehicle speed in a downhill descent?
Yes, it is.
By using the engine to help control speed, we now have greater levels, margins, of safety as we are engaging the engine, brakes, and tires.
Thus, we've spread the frictional load among three systems rather than just two.
Does engine braking really create that much stress so as to greatly increase wear and tear such that using engine braking will break the engine sooner rather than later?
The point really is, we have more than just the brake system and the tires to help us control descent speed, and do so safely for the health of the brake system, engine, and drivetrain.
Spreading the work means that each system takes on less stress, wear, and tear...well except for the tires.
If you ride the brakes to control speed, then you may overheat the brake parts, which leads to having to replace them sooner, not to mention the loss of braking power and control, which can result in having to replace your whole vehicle, and maybe a knee, elbow, or hip.
If you can engage your engine to help assist the brakes, then you're providing yourself better control of your vehicle as you spread the load.
A vehicles engine is capable of creating such force that it can overcome a heavy stationary object, and cause it to start moving and accelerate.
Using the engine to help control descent speed, and using your brakes as needed with that, is a good thing.
Last edited by TT-S4; 04-15-2022 at 08:59 AM.
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04-14-2022, 01:14 PM
#8
I live at 2100 ft. My commute consists of a long descent along a ridge, and then a drop down to sea level, a total of 8 miles. If I'm the only car on the road I can make the whole thing without touching the accelerator and hardly touching the brakes.
The issue is when I'm behind someone who feels the need to brake sharply before every slight curve in the road, or to go 15 mph below the speed limit. In that case I would like to paddle shift to a lower gear to avoid overheating my rotors and to save brake life.
What I'm concerned about is that for the whole 8 miles the oil temperature still hasn't warmed up enough to even register on the readout. So running the engine to high RPM even though it's not putting out power probably isn't ideal. On the other hand, modern low-viscosity oils are pretty good even at low temperature.
What's everyone's opinion, use the brakes and keep the engine RPM low until the oil actually warms up, or use engine braking and keep the brakes and rotors cooler?
The issue is when I'm behind someone who feels the need to brake sharply before every slight curve in the road, or to go 15 mph below the speed limit. In that case I would like to paddle shift to a lower gear to avoid overheating my rotors and to save brake life.
What I'm concerned about is that for the whole 8 miles the oil temperature still hasn't warmed up enough to even register on the readout. So running the engine to high RPM even though it's not putting out power probably isn't ideal. On the other hand, modern low-viscosity oils are pretty good even at low temperature.
What's everyone's opinion, use the brakes and keep the engine RPM low until the oil actually warms up, or use engine braking and keep the brakes and rotors cooler?
If so, then you need to let your engine, and oil, warm up a bit before that rare scenario.
My S4 engine heats up to normal operating temp in about 1.5-2 miles at steady 30-40mph speed. This is on relatively flat roads, where my engine is producing power, and heat.
Even in winter with temps not much above 0F, the same steady speed gets me to operating temp in about 2-3 miles.
I'm very surprised that your engine hasn't warmed to operating temp within 8 miles.
However, if you are really firing up your engine, and then heading down a hill, where you don't need any engine power, then again, warm that engine a bit longer before heading out.
It seems that with Audi, even the current models, thermostats are a not too uncommon failure.
Just in case, if your engine is taking that long to warm up, even to show/register lowest heat reading, then have your thermostat checked out.
Here's a positive, as our cars use fully synthetic oil, and a LOT of it, 7.7 quarts.
Synthetic oil's have much, much greater cold flow rate, meaning they actually still flow at very cold ambient temps, well below 0F.
That is why synthetics are much better at protecting an engines longevity over time, for vehicles that are used in very cold environments.
In the old days of conventional oil, many would start and idle their engines for 10+ minutes, in order to get engine temps up, and all parts warmed, before adding the stress of accelerating and high engine whirly bit speeds.
Synthetic oil has greatly mitigated that need, giving us much greater engine part protection and greater engine longevity.
Last edited by TT-S4; 04-15-2022 at 08:52 AM.
04-14-2022, 04:50 PM
#9
Concern for engine braking may be due to a legitimate legacy condition. Carburated engines used air flow to meter fuel and under high vacuum pulled excessively rich mixture. Prolonged downhill braking caused oil dilution by fuel. If you had a coolant temp. gauge (probably had to fit one) you could see the rapid temperature drop.That was then.
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TT-S4 (04-15-2022)
04-15-2022, 08:51 AM
#10
Concern for engine braking may be due to a legitimate legacy condition. Carburated engines used air flow to meter fuel and under high vacuum pulled excessively rich mixture. Prolonged downhill braking caused oil dilution by fuel. If you had a coolant temp. gauge (probably had to fit one) you could see the rapid temperature drop.That was then.
Arguing for an extreme is never a good way to come to reasoned and reasonable conclusions.
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Nakedhoof (04-15-2022)