Why does multiple short trips = horrible gas mileage?

[thenexlevel]

Even properly warmed up, I noticed if I take a few trips (post office, blockbuster, restaurant, etc.) all about 2-5 mile each trips kills my fuel economy.

For example on my daily driver saturn, I can get about 100-120 miles per 1/4 tank on highway but if i take about 3-4 short 2-5 mile trips, it would kill about 1/4 of my 1/4 tank. This is all after the car is already warmed up so its not due to cold starts...over the course of a weekend I can use up 1/4 tank with only maybe 20-30 miles worth of short trips.

This is the same with the other cars I been paying attention to recently, my G35 and my girl's murano...any explanations you guys can give of why this happens?

 

[astrodudepsu]

acceleration my friend, buring through gears hurts fuel. highway is better because (in theory) you are maintaining a constant speed.

plus auto trans aren't the most effcient if you are using an auto.

 

[bubbrubb]

Odds are you're sitting at stoplights and having to start/stop a lot. Lots of work for the engine, not a lot of distance covered. Thats what I've noticed anyway. Short trips and lots of idling really helps my hummer live up to the stereotype.

 

[thenexlevel]

I realize city driving is going to give a lot worse than highway, but even in stop and go traffic seems to net better fuel econ then short trips where you have to turn off/turn on the car...i'm driving like a grandma too with my saturn lol.

 

[bubbrubb]

I realize city driving is going to give a lot worse than highway, but even in stop and go traffic seems to net better fuel econ then short trips where you have to turn off/turn on the car...i'm driving like a grandma too with my saturn lol.

yeah, I see what you're saying... same thing happens to me here. :nonono:

 

[HotRodK]

I know here in Orlando (and any other city) when your sitting at redlight after redlight, you MPG is ZERO. Then you have to accelerate away from each light. Not good for mileage.

Now your saying when you go from store to store, for example, your getting WORSE mileage than light to light?? Is this hand calculated mileage or on the overhead display? An idling engine is far worse than a engine turned off.

 

[harry gilbert]

It takes a lot of energy to accelerate a mass to speed. It takes less energy to keep the car moving at constant speed (only fighting wind resistance and friction of moving parts). Then, when you brake, that energy is dissipated (lost) as heat through the brakes. Thus, a series of short stop-and-go trips uses much more gas than the same distance done as one trip at constant speed. :read: a physics book about potential and kinetic energy.

 

[tjs98gt]

because the ECU never enters closed loop operation?

 

[LS2GTO]

On the highway you are traveling at speeds of over 60mph with an rpm in the 2000 or so range (cruising). From a dead stop you are revving the engine up to 2500 (or whenever you choose to shift) and are going 0-15mph.

As you can see, your engine is working just as hard (same rpm range), yet you are covering much less ground so your mileage sucks. Plus like mentioned before, and engine works alot harder to get a 3000+lb hunk of metal moving from a dead stop than just simply keeping it going at a constant speed.

Think about planes for a second. The engines are working at close to max speed just to get the thing of the ground, then when up at cruising altitude they can pretty much shut them down to almost 0 throttle and still keep going. Yeah there's that whole lift thing that can keep a plane in the air w/o power, but still tho, they barely use 35-40% throttle at cruise.

 

[canibus]

i've also noticed that when i fill up the tank all the way. i can make the same trip more times. for example, i can drive 30 miles on a full tank 20 times. if i have half a tank i can drive 8 times fill up to half again and i'll drive another 8 before empty. that's 16 compared to 20. weird i know

 

[golden_eye]

Think about planes for a second. The engines are working at close to max speed just to get the thing of the ground, then when up at cruising altitude they can pretty much shut them down to almost 0 throttle and still keep going. Yeah there's that whole lift thing that can keep a plane in the air w/o power, but still tho, they barely use 35-40% throttle at cruise.

That's not true. Piston-powered aircraft generally cruise at 65-75% power in level flight. The reason they use less fuel in cruise is because you lean out the mixture as you climb to account for the lower air density. Your true airspeed also increases as you climb for the same reason. Even airliners cruise at 80% of their max RPM or more when they are up at altitude but they burn significantly less fuel than at lower altitudes due to the lower air density requiring less fuel to maintain an ideal mixture.

Lift won't keep a plane in the air forever without thrust.

 

[JasonSnake]

because the ECU never enters closed loop operation?

more like this. Even if the car is already warm, every time he starts the car, the ecm is in open loop for a very short time only. During this time, the ecm is pumping in some extra fuel for the first 30 seconds to a minute.

Ever pay attention to your exhaust? Listen to it next time when you start the car when it's already warm. The exhaust sounds like it's gurgling more

 

[goingup]

At the stop light just turn your car off. Then restart it when the light ids green. That is what every hybrid car does which explains why they get better mpg in the city.

 

[bubbrubb]

At the stop light just turn your car off. Then restart it when the light ids green. That is what every hybrid car does which explains why they get better mpg in the city.

I think the electric motor might help a little bit too lol. They can run on just those. One snuck up on me in a parking lot. Scared me cause it was just whirring down the lot right at me (hybrid drivers are usually ham fisted idiots, fear them.)

 

[bossvt]

I have one of those instantaneous MPG computers in the Volvo and I've learned a lot from it. Getting the best gas mileage is all about the rate of acceleration. Quicker you accelerate (and frequency), the worse your mileage will be. Short trips are acceleration intensive, meaning higher percentage of time spent accelerating than at a constant speed.

 

[01svtL]

i've also noticed that when i fill up the tank all the way. i can make the same trip more times. for example, i can drive 30 miles on a full tank 20 times. if i have half a tank i can drive 8 times fill up to half again and i'll drive another 8 before empty. that's 16 compared to 20. weird i know

Because when it's "full," the dial is above the "F" and it takes some distance to actually bring it down to the F. You went further when full, but you also used more gas.

 

[VirtualSVT]

At the stop light just turn your car off. Then restart it when the light ids green. That is what every hybrid car does which explains why they get better mpg in the city.

a/c > any tiny increase you might see..

 

[canibus]

Because when it's "full," the dial is above the "F" and it takes some distance to actually bring it down to the F. You went further when full, but you also used more gas.

good point never thought of that

 

[PowerWheels]

Screw Mileage