Milage variability Vs trip lengths. - PeachParts Mercedes-Benz Forum

networkboy · #1 02-10-2007, 03:17 AM

Hey all,
As you can see in my sig I've had some impressive variability in the mpg I get from fuel. The 17mpg tank was burnt almost entirely with work commutes (~10 miles each way), while the 22mpg tank was predominately longer trips / more trips in a day where the engine has not cooled down too much.

The fuel came from the same station and had the same additive package. Can the trip length make that much of a difference in economy (over 5mpg)?
-nB

pawoSD · #2 02-10-2007, 03:22 AM

With all the idling and reving (spinning...) I do in the winter traveling around the snowy city roads, I am sometimes lucky if I keep it above 17mpg!

Then if I fill up and take a freeway trip...I get almost 24....shows just how much fuel is wasted when driving around the city. Presently I have only driven about 223 miles on my current tank, and I am almost down to 1/4 tank remaining!

About 65% of it has been in the city on this fill-up....

barry123400 · #3 02-10-2007, 03:23 AM

This time of year especially in my opinion. You consume exra fuel to adjust for the thicker cold oil on short trips like ten miles for starters. All the other fluids take time to thin out as well. Just a lot more drag on the car.

pawoSD · #4 02-10-2007, 03:25 AM

Quote:

Originally Posted by barry123400

This time of year especially in my opinion. You consume exra fuel to adjust for the thicker cold oil on short trips like ten miles for starters. All fluids the other fluids take time to thin out as well.

Very good point....its been below 18F most of the time here for the past 3 weeks so far....and I always drive less than 15 mins usually in the city....so I am just about to operating temp by the time I reach my destination and shut it down. I am also more prone to leaving it idling/running to save wear on cold starts etc...which also uses up fuel...

Ara T. · #5 02-10-2007, 06:48 AM

Around town I have never gotten below 20 mpg. My commute to school is 15-20 minutes and the engine is definitely warmed up by then as the oil pressure has dropped to 2 BAR.

pawoSD · #6 02-10-2007, 11:35 AM

My commute is just over 4.5 miles and takes about 12-16 mins depending on traffic, its all slow driving, 35 for the first 1/2 mile....then 25 the rest of the way....so I am just barely to operating temps (when its this cold out) by the time I am there or home. My work is 2.6 miles from my house, but I can go 50 down that road....and am almost to operating temp in that same distance. Its the slow driving that never lets the engine heat up.

softconsult · #7 02-10-2007, 11:53 AM

I don't understand the point. This is simply re-stating the obvious.

When a car is up to speed and cruising down the highway it takes very little horsepower. When you are doing city driving it takes more energy to move the car from stop up to speed.

It's been known for a very very long time that you will get better mileage in highway driving versus city driving. That's the reason there are fuel economy rating for city and highway.

Steve

networkboy · #8 02-10-2007, 01:35 PM

I was still city driving, it was just that the bulk of the trips were longer.

vstech · #9 02-10-2007, 01:58 PM

at idle at a light, you get 0mpg, when you step on the throttle, you have to build up energy to overcome inertia wanting to hold you still, and you are turning the motor using fuel at a lower gear, going fewer miles per Revolution. also the torque converter has the most slip at lower speeds. the shorter the trip the lower the economy due to all the starting of the motor, the improper motor temp/operating efficiency and all... it just makes sense. the more time you spend at speed, the better your mileage will be.
unless you drive a hybrid vehicle. the hybrid uses the electric motor in most stop and go driving, so it actually gets better mileage in the city than on the highway... not that I would ever drive one... just stating the facts.
John

t walgamuth · #10 02-10-2007, 02:20 PM

you can have that much variability in just recording/ filling inaccuracy.

take your averages for 20 tanks and you will have something.

tom w

tarbe · #11 02-10-2007, 04:06 PM

I am amazed at how little my mileage varies from tank to tank.

100% commute (12 miles each way in Houston...20 stop lights and some days seem to hit every other one) vs all highway miles...has not varied more that 2.5 mpg max.

I always fill the tank to the brim to eliminate filling discrepancies. My tanks have run from 29.8 to 32.3mpg. The 32.3 tank was just today and included quite a bit of commuting.

I accelerate very gently, as you have probably figured out.

Tim

captainmonk · #12 02-10-2007, 05:37 PM

my father would love you Tarbe he figured many years ago 53 was the best speed versus fuel economy So next week if anyone sees a siver 86 SDL cream puff slowly heading towards Fla wave and say hi Bill In the passenger seat will be Janet cringing knowing she's in gonna get run over by a semi as her husband worries about his mpg's

tarbe · #13 02-10-2007, 06:05 PM

Quote:

Originally Posted by captainmonk

my father would love you Tarbe he figured many years ago 53 was the best speed versus fuel economy So next week if anyone sees a siver 86 SDL cream puff slowly heading towards Fla wave and say hi Bill In the passenger seat will be Janet cringing knowing she's in gonna get run over by a semi as her husband worries about his mpg's

Are we related?

I cruise at 60 - 62 when on the interstate, if traffic allows. I'd go 53mph if I was retired and had more time!

vstech · #14 02-13-2007, 10:08 AM

hmm, at 53mph, I don't think you have enough inertia to clear hills. 58 to 65 is probably the most efficient speed. unless you have overdrive... then 68-75 is better.
John

softconsult · #15 02-13-2007, 10:37 AM

I do a lot of interstate traveling.

In my experience those folks, thankfully very few, who insist on driving below the speed limit are a traffic hazard. Everybody, including semi's has to pass them. The bulk of traffic is around 5 over the limit, so the guy doing 60-62 on a 65 or 70 mph in order to save fuel is risking his life and indirectly increasing the risk to other drivers.

Couldn't resist. It just drives me up the wall when I see it happening.

Steve