Economy Driving With a Manual Transmission

fuel-economy

#1

I’m trying to fine tune my driving style to get the best economy with my 5-speed Scion tC. My question is this: With the motor running, is it better to coast in nuetral or a very tall gear (such as 4th or 5th) when approaching a stop. I’ve heard on the show, modern fuel injection often times cuts the supply of gas when slowing down in gear, while putting it in nuetral still supplies gas to make the motor idle. Does this information apply to manual or automatic transmission equipted cars? It would seem that coasting in a tall gear would make more sense. My second question: If you start the car, it injects more fuel than normal to help startup. If you turn off your car at a stoplight, how long does the wait have to be before it will be worth it to turn your car off? My Scion idles up fairly high upon startup, so I’m thinking it injects a lot of gas. Any help with this is appreciated!


#2

I too have tC. I love it. My son bought one too. He also loves his.

you’ll be hard-pressed to measure any difference in gas mileage between the two scenerios you’re describing. The difference will be too miniscule to measure.

Don’t turn it off. Let’s assume you make 20 stops at red lights every trip, make 4 trips a day, and keep the car for 5 years. If you shut it off only at the end of every trip, you’ll be putting wear on the starter motor and its components 7,300 times. If you shut it off at every stoplight, you’ll be putting wear on it 142,400 times. Get the idea?


#3

modern fuel injection vehicles have fuel cut off on the overrun,which means when youre driving at over 1500rpm on the tachometer,and you take your foot off the gas,it will cut the fuel off,handy when your going downhill or just slowing down,but below 1500 rpm the fuel cuts back in to prevent stalling,so leave it in gear,not neutral!i presume it only works for manual transmissions because autos go almost back to idle when u take your foot off the gas.its worth turning off the engine at stoplights if they stay on red for more than a minute.i tried it for a week and got 2 mpg more!


#4

My guess is keeping it in gear will use more fuel, because the IAC will be giving it throttle to match engine RPM for smooth operation while slowing down


#5

I understand the trade-off from wear and tear on the starter motor. That fact has crossed my mind. When I turn the car off at a light, I use a fair amount of judgement. A situation where I’d do this would be if I saw a green a long ways off and knew it was going to turn red soon. I’d coast with the engine off and come to a stop. From the times I’ve done this, I’ve felt it’s worth it. How many people do you know that get 33 MPG from a tC? Why the heck is 5th gear so low on these cars?


#6

Personally I’d rather not have that wear & tear. I define “tear” as that fluid droplet that forms on my eye when I get the bill for a new starter motor assembly.

Just kidding. 33mpg is definitely good, but i’d bet that if you let the engine run and made no other changes to your driving style you’d still get 33mpg. Try the experiment for a month and let me know how you make out.


#7

If you are approaching a stop and your speed is still too hot to coast to a complete stop in neutral, then coasting in a gear that has the engine turning more than 1500 rpm will cut off the fuel. If the engine braking will stop you too soon, it’s best to coast in neutral.
If coasting with engine off, be sure to turn the switch back on to run position after the engine dies, or your odometer will not register the miles you coasted and your apparant fuel economy will actually go down even though your actual fuel economy will be higher. No need to wear out the starter, just put it in fifth and let out the clutch and you have a running engine if your car is going any faster than 20 mph or so.
High peak speeds are gas mileage killers. Do your best to drive the highest possible average speed with the lowest possible peak speed. This means accelerating a lot more briskly than a lot of people think is optimum.

I have been averaging about 44~45, my best tank 45.8 mpg with a Toyota Yaris manual transmission.


#8

If that were the case, engine braking would be impossible and the thing would alarmingly speed up when going down hills!


#9

You have to stop thinking about specific things. Just try not to approach stops at high speeds. You will save by coasting up to a stop instead of braking hard.


#10

In a manual tranny why does it matter? You disengage the clutch and then brake either way.