Living in a hilly area, I save my brakes by using the car engine to slow the car.
I notice that when I go into the lowest gear, the engine seems to race.
I have three questions regarding this practice:
1) Does this harm the engine?
2) Does this harm the transmission?
3) When slowing down via the engine, and the engine makes that racing noise, is extra gas being pulled into the engine? Or to put a finer point to it, is more gas used when slowing down this way?
- No, if it doesn’t go up to or above the red line.
- No, it’s less effort on it than going up the hill was.
- You don’t give the year, but just about all newer cars completely turn off fuel to the engine when coasting in gear.
You should be in the same gear going down a hill as you would use going up.
Twotone
Brakes are Much, Much, cheaper than engines and transmissions…
In all my years of driving I have never heard that, probably due to being a flatlander, That is inspirational. I had a rental car in the mountains that the cruise control performed all the functions of up and down shifting admirably, maybe it is like the kids in grade school, they don’t have to use a pen and paper because they have calculators, you don’t have to know how to drive a car because you have cruise control.
I assume this is a manual transmission. You had better be VERY good at coordinating the engine speed during downshifts, or you’ll be wearing out your clutch. As already said, brakes are way cheaper than a clutch.
Downshifting one gear (automatic) when going down a steep hill keeps the brakes from overheating and possibly fading. This is a safety measure to save the brakes; it has nothing to do with fuel consumption.
When going up a steep hill (mountain) I shift down with the automatic, in order not to lug the engine unduly. If you have a manual 5 speed gear box, I would go up a mountain pass in 3rd gear.
The “kickdown” gear that other refer to is for PASSING and to be used for a very short time. Using the kickdown gear to go up Pike’s Peak, for instance, would be hard on the transmission.
#1 Brakes are far cheaper than transmissions.
#2 On long downhill situations, it is safer to use engine braking because the brakes can overheat.
#3 Over doing it, can cause wear on the engine and transmission. Both of which are far more expensive than brakes.
Using engine braking may or may not save fuel. Many modern computerized cars, turn off all fuel to the engine when using engine braking. That means free miles, even better than coasting in neutral.
#1 Brakes are far cheaper than transmissions.
Just driving a car “wears” the components, and short of storage, all driving “harms” components in some way. The question is always, which ones are the safest, and most economical to use over time for each given task. Fortunately, the people who make the cars give you a pretty good general idea how to use each in the manual. IMO, safety trumps excessive wear worrys every time. Many new cars automatically down shift not only in cruise, but in regular driving. It’s generally safer, more economical over the long run and when done correctly, easier on the components that are expected to do that task.
Be aware, downshifting in some conditions (ice example) and not using the abs may be more dangerous and shorten the life of the most important component, you. So there are no absolutes, just guidelines.
When electric drive motors are the norm this question will be mute as we’ll be in gear all of the time and brakes and “engine braking” will be an integrated task like they are on much “equipment” other than cars today.
I’m so concerned about harming the transmission (“tranny” to those in the know) that I don’t even use the engine to make the car go FASTER. Someday science will give us a car without either an engine or a transmission so we don’t have to worry about harming those parts.
Exactly.
Actually, I think that rule came from the trucking industry. When you are carrying 50,000 pounds of cargo, your weight can really make you accelerate down a hill a lot more than you would in a car. However, with recent improvements in aerodynamics and engine design, this rule has been amended for newer trucks. The new rule is you should descend a hill after dropping one or two gears lower than the gear you used to climb the hill.
Since most cars don’t have the weight to make them accelerate going downhill, I question whether this trucking rule should be applied to cars. Today’s cars can be downshifted after you have already begun your descent, and the brakes can easily be used to regain control without overheating them.
I really do not believe you got me to post, I’m a girl who knows just enough to be truely dangerous. But I can speak from experience, when I was in my youth, 1983 and 19, I had the great furtune to own a 1968 Camaro. Because I believed what I heard, about saving the brakes by shifting into low (an automatic transmission) to brake, in city traffic, I’d slow my roaring car at every annoying red light I came to, in low gear. After about a year, I managed to beak the poor thing’s back completely. I would say, that if you love your car, do not do this… it’s just wearing on every portion of the engine.
There you haveit folks, my entire two cents. 
What you did (use the transmission to slow for a stop), is not at all what the OP is asking about. He’s asking about down shifting while going down a hill to hold his speed down, not to slow down or stop. This is not only okay, it’s exactly what many higher end cars do all by themselves.
Even the brakes of a dedicated sports car such as the Nissan 370Z can fade after 7 panic stops. I think that using the engine to control a downhill speed is a legitimate technique in ANY vehicle.
They have now. It’s called public transportation
I am of the view that extra gas is used during engine braking contrary to popular opinion here on Car Talk which is that modern engines shut down fuel delivery when coasting. One of our cars has an instant fuel mileage computer that maxes out at 99 mpg.
By the comparing the speed of rise to 99 mpg when either coasting in neutral (clutch disengaged) or leaving the driveline engaged, more fuel is used when the driveline is engaged. It would then follow that higher engine coasting speeds will use more fuel.
The difference, however, is very small. Gross amounts of fuel are used when accelerating. My 35 plus mpg rated car sees less than 12 mpg even when weakly accelerating from a stop.
I think that downshifting a gear or 2 going down a steep hill is not a bad idea. But LOW Gear, I don’t think so. Of course it’s a trade off, downshifting does put a slam on the tranny, u-joints, and engine and engine mounts.
That would be interesting if weight had ANYTHING AT ALL to do with acceleration due to gravity. This is not just first semester physics, it’s FIRST WEEK physics (in high school).
Why would you use your brakes “to regain control”? At what point did you lose control?
Anyway, you’re wrong.
Yes, but that’s for … YOU know…