Downhill in gear

General discussion about cars. Looking to buy a new car? Have a great driving story? Post it here!
Post Reply
Stelcom66
Senior Standardshifter
Posts: 133
Joined: Fri Oct 05, 2012 9:47 pm

Downhill in gear

Post by Stelcom66 »

Does going downhill in gear, such as 3rd (of 5 gears) on a moderate decline - use any fuel? I thought not, since as long as the accelerator isn't depressed. I've been doing that over the years assuming it would preserve the brakes just a bit. I've read in other forums it's not advisable, causing wear on other components, with the theory brakes are typically less expensive to replace than transmission components. Still, I'd think any stress on the drivetrain or fuel usage (if any) while coasting downhill in gear would be minimal?
IMBoring25
Moderator
Posts: 3411
Joined: Wed Jun 11, 2003 5:01 pm
Location: OK, USA

Re: Downhill in gear

Post by IMBoring25 »

With respect to the first question, it depends. Many newer cars can completely shut off the injectors in a mode commonly called DFCO (Deceleration Fuel Cut-Off), but older injected vehicles and especially carbureted ones will probably keep some small amount of fuel flowing. That amount of fuel is unlikely to materially be affected by the gear selected unless you have to use throttle to maintain the desired speed, however.

With respect to the second, there really is minimal wear, especially if you double-clutch the downshift. The only exception would be if you force the shifter into a gear completely inappropriate for the speed you're traveling and mechanically overrev the engine or drivetrain.

It can actually be dangerous to descend long, steep grades without downshifting. While being used, brakes and brake fluid heat up. This causes them to become less effective (brake fade) and if used for a long time without being allowed to cool can even lead to complete failure.
Stelcom66
Senior Standardshifter
Posts: 133
Joined: Fri Oct 05, 2012 9:47 pm

Re: Downhill in gear

Post by Stelcom66 »

Then it sounds like I should be doing what I've always done. Use common sense and what 'feels' right. A few years ago I lost the brakes on an older Honda Accord I had, a leak in the lines. Was very fortunate that I wasn't too far from home, but more fortunate that it was a standard shift where I could slow down enough to be safe.
User avatar
ClutchFork
Master Standardshifter
Posts: 1917
Joined: Wed Mar 06, 2013 2:55 pm
Cars: 2008 Fusion 2.3L manual
Location: Detroit MI

Re: Downhill in gear

Post by ClutchFork »

Yep, in gear on down hills if there are much of a hills. In the Rocky Mountains and other mountains you really have to keep it in gear.
Stick shiftin since '77
theholycow wrote:Why in the world would you even want to be as smooth as an automatic? Might as well just drive an automatic...
Post Reply