downshifting and gas mileage

[rdsworks]

I was just wondering how much of an effect downshifting(on the 6speed) will have on the gas mileage of a car.

I've looked around and apparently when you downshift and the rpm's are higher then 1800 the fuel injecters stop providing the engine with fuel...is this true?

Anyone test this. I started to downshift religiously just to see if there will be any difference (i get around 28-30MPG lifetime).

[kc5f]

If you downshift to pass, wouldn't having the fuel injectors stop providing the engine with fuel sort of defeat the purpose?!

[biggie]

There's no way the engine should lean itself out, it would die.

You will get slightly less mpg by downshifting, not sure if its hardly noticable. Its just a decision, wear out engine/less mpg OR wear out the brake pads faster. To me its about a toss up, but I do downshift out of habit.

[rdsworks]

sorry, I meant downshift to slow down in traffic, instead of coasting and breaking to a stop.

I'm just trying to figure out the best way to drive the car since I taught myself how to drive standard on it...

[aleckz]

Downshifting to slow yourself down isn't that great of an idea mainly because a transmission is much more expensive to fix or replace than brakes. Use the brakes, you're not racing your car anywho.

[Merc1980]

I was just wondering how much of an effect downshifting(on the 6speed) will have on the gas mileage of a car.

I've looked around and apparently when you downshift and the rpm's are higher then 1800 the fuel injecters stop providing the engine with fuel...is this true?

Anyone test this. I started to downshift religiously just to see if there will be any difference (i get around 28-30MPG lifetime).

I believe you mean redlining. Yes, normally when you hit the rev limiter engines used to use a fuel cut in order to stop you from reving past it's recommended limit. I believe they now use a spark cut on newer cars so there is less chance of detonation issues.

Do a search on hypermiling and it will give you an idea on what revving your engine can do to your fuel economy.

[xtwoonamatchx]

well you will definately lose fuel economy, not so much from tank to tank, but overall it will be a loss, because if you just put it in neutral and brake, your revving about 800 (i believe thats idle) but, if your downshifting, you can rev between 5k and probably 2.5k (dont think the engine brakes that much below that) so you do the math or the time spent in the 2k+ to the 800... just my opinion... if im coming to a light that may turn green... i keep my clutch in, and usually put it in 3rd, so when the light is green you can go...

[DejaWiz]

I thought that as long as the car was coasting with no pressure on ye ole throttle pedal, it will cut the fuel flow (not just above 1800 RPM).

[xtwoonamatchx]

thats in automatics, they take it out of gear... i believe... but in a stick shift it is always in gear unless the clutch is in or its in neutral.

[motoguy128]

I still prefer to downshift, just my preference. For saving fuel, leavign it in gear uses marginally less fuel than neutral. How... well on newer cars with drive by wire throttles where the computer has complete control over the throttle. When no throttle is requested, the ECU can cut the iginition and fuel simultaneouly... it's electronic ignition, os they are completly sychronized... there is no possibility of detonation, lean lixture etc. This saves fuel because the power to run the alternator, oil pump, water pump and just the normal internal friction of the engine can be generated by the inertia of the car. It's free power. So on that long hill, you're better off leaving it in a high gear, then putting it in neutral.

I think you can feel the transition. When you initally lift throttle there is some engine braking, a few seconds later the engine braking increases slightly.

Also, it's not safe to operate a car in neutral, you have no ability to accelerate and emergency handling is compromised.

Even if you don't downshift, you still want to leave it in gear until the engine speed is under about 1500 RPM. At higher speeds, it defnitely worth at least one downshift... for example when comming off the freeway. A downshift to 4th or 3rd helps save the brakes and reduced the possibility of warping the brakes if you will be comming to a complete stop..

[DejaWiz]

^ Motoguy just nailed it.

^^ transmission has nothing to do with it.

I had an '03 GTI 6 spd with the trip computer that gave real-time MPG and updated every second. When I'd let off the gas and coast, the MPG would increase substantially after every refresh. Would go from, say, 22, then to 68, then 112, then 135, then 174, then when it got above 199, it would simply read "- -". I think I read over at VWVortex or VWFixx that this was due to the computer shutting off the fuel and just about every modern vehicle does this.

[Juelze]

Clutch is for go, brakes are for slow, IMHO. BTW, if you are in a 35mph zone, is there a benefit from going from 4th gear (what I usually do) to 5th or 6th gear?

[xtwoonamatchx]

thats what i do, i was taught to be in the highest gear possible... but if you need to accelerate you should downshift, because.. say in 6th gear at 40MPH you have no torque and even if you floor the pedal your still not going anywhere, and a friend told me it puts more strain on the engine, dont quote me as to whether its true for the DBW, but for regular throttle cars it is, but thats just my personal opinion, someone else here might have another suggestion.

[my_new_v]

thats what i do, i was taught to be in the highest gear possible... but if you need to accelerate you should downshift, because.. say in 6th gear at 40MPH you have no torque and even if you floor the pedal your still not going anywhere, and a friend told me it puts more strain on the engine, dont quote me as to whether its true for the DBW, but for regular throttle cars it is, but thats just my personal opinion, someone else here might have another suggestion.

Becareful when in 6th gear going 40mph. The was another thread about that and how it bogs down the engine so your ultimately using more gas than needed. I also thought that, read that thread, and then paid more attention and realized that 6th gear...40mph, makes the engine struggle a bit. 5th gear isnt bad at 40 though.