Freeway stop and go fuel mileage question..

I know, weird question, but does anyone know if driving in freeway stop and go traffic significantly reduces, say 20%, fuel mileage? BTW, I drive gentle, don't floor it every time there is an opening or when traffic clears.

I would say yes. I think that freeway stop and go is the worst for mileage. 0 to 60 and back again, over and over.
If I drove on flat ground at 45 mph, I'd probably get 33 mpg. So 17 mpg is half, and that is what I get in city driving.
I noticed that driving 100 yards behind a big semi will give me about a 1/3 higher mpg reading than being in the other lane at the same distance.
I picked up 3 mpg by changing my air filter. It was dirtier than the interval would make me think.

If you drive like the truckers do and leave a large gap in front and keep the van rolling will help off-set some of the hit you take in the loss of MPG. Momentum is your friend.

In city stop-and-go traffic, i can achieve 20 to 25% better mpg (and gph) by shifting into neutral when stopped.

--dick

autostaretx said:

In city stop-and-go traffic, i can achieve 20 to 25% better mpg (and gph) by shifting into neutral when stopped.

--dick

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Traditionally, I thought manual transmissions had a mpg advantage over automatics due to torque converter slippage and fewer gears. With today's lock up torque converters and huge number of speeds in automatics, I thought they had evened the field with manuals. If the description above is true (which I assume is due to load on the engine through the torque converter at idle), it would mean manuals still have an advantage in stop and go driving (unless the car has automatic engine shutoff).

Oh, how I wish I could get the Sprinter as a manual in the US. I own 9 cars, 4 motorcycles and a tractor, and only one is an automatic - the Sprinter...

I try to take advantage of the good view in a Sprinter when driving in heavy freeway traffic. Slow early and try to avoid using the brake. Every time you touch the brake, you're converting forward motion you paid for by burning fuel back into heat. The less you use the brake, the better mileage you're going to get. When I see brake lights 3 or 4 cars ahead, I get off the gas pedal. Try to convert the stop-and-go around you to slow-and-go. That's also why following a big truck in traffic like this helps. They're usually pretty good at maintaining a steadier speed than the cars around them.

Yes, your fuel mileage goes down in heavy freeway traffic. I don't think it would be as much as 20%, but 10% is very believable.

When you are stopped you get 0 mpg. On our three cars with instantaneous mpg readouts (two Subaru H6’s and a Tahoe) mpg accelerating in the lower gears is also very poor.

Answering the question another way, the lowest mpg I’ve gotten per tank with mostly (70%) city driving was 21.9, while 30/70 tanks are much higher: 24 or a little more.

We also had a Cruze turbodiesel that also got relatively good city mpg relative to the gas turbo model. The TD averaged 40 vs 32 for the gas model, called the Eco. They were nearly identical other than engine.

autostaretx said:

In city stop-and-go traffic, i can achieve 20 to 25% better mpg (and gph) by shifting into neutral when stopped.

--dick

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Never seen that in any vehicle in 20 years of city driving. We have a Subaru that vibrates in drive when stopped so we often do this, and it does no better than our other Subaru that does not. They both have instantaneous and accumulated mpg readouts.

Working from memory, i see 27% LOD in neutral, 35% LOD in "D" when stopped. Headlights on.
(i don't normally have GPH displayed, so i'm not going to try to recall from years back when i first noticed the effect)

Yes, i realize LOD is a calculated/fabricated number, i view it as "indicative" as opposed to "firmly quantitative".

There was a period (10 years ago) where my Sprinter use was primarily two 4 mile commuter trips per day for many months. If i was moderately religious about the shift-to-neutral, it even showed up in the tank-to-tank filling mileage results. (18.5 to 19.3 versus 21 to 23) ((i wasn't *that* religious))

--dick

My LOD numbers do the same bump between Neutral (28%) and Drive (39%),
TC slip goes from ~zero in Neutral to engine rpm, and spinning the TC turbine at 680 rpm takes work.

My MAF/O2 litres per hour calculator (the top middle value) drops by about 20% from 1.33 l/hr in Drive down to 1.07 l/hr in Park or Neutral.
I recall that hitting the A/C button is good for another 0.15 l/hr? Now I’m curious... time for a quick spin around the neighbourhood.

-dave

(edit: you can also see how the TCM reports the engine coolant temperature while in Park or Neutral, and the actual ATF temp when it is in gear)

metaldirtart said:

I know, weird question, but does anyone know if driving in freeway stop and go traffic significantly reduces, say 20%, fuel mileage? BTW, I drive gentle, don't floor it every time there is an opening or when traffic clears.

Click to expand...

Highway stop and go wouldn't be any worse than typical city traffic.

I get 22 almost everywhere on the highway at 70 MPH, but I do work in Los Angeles somewhat often and I deal with plenty of traffic there, those tanks are usually 21 MPG.

I have a 2003 158" high roof.

https://sprinter-source.com/forum/showthread.php?t=25864&highlight=LOD

bill in tomahawk

To add some background information, my newish to me 2005, long, and tall Sprinter gets very good mileage, I don't lead foot it, easy on the brakes... My around town, and back roads 45-55 mph commuting mileage is usually 25, + or -, unloaded. Early on I did a five hour freeway/highway trip, with three medium mountain passes, loaded with 1200 or so pounds of gear, and got just over 25 mpg, cruise control set to 64/5 actual mph. Now, every month I do a 260 mile, roundtrip freeway trip with the same load, and only get maybe 21 mpg. I had been attributing it to the RSN mod/fix, but recently thought about the fact that on the return trip there is always similar, longish stop and go sections, ALWAYS, it is California after all, so I thought I would ask opinions about the associated mpg drop. I had been considering reversing the RSN fix mod, but will wait until I can do some more freeway trip tests. Thanks for all the input.

Nautamaran said:

My LOD numbers do the same bump between Neutral (28%) and Drive (39%),
TC slip goes from ~zero in Neutral to engine rpm, and spinning the TC turbine at 680 rpm takes work.

My MAF/O2 litres per hour calculator (the top middle value) drops by about 20% from 1.33 l/hr in Drive down to 1.07 l/hr in Park or Neutral.
I recall that hitting the A/C button is good for another 0.15 l/hr? Now I’m curious... time for a quick spin around the neighbourhood.

-dave

(edit: you can also see how the TCM reports the engine coolant temperature while in Park or Neutral, and the actual ATF temp when it is in gear)

Click to expand...

Nice work!

That’s almost 20% reduction - while you are in neutral. How much time you can spend in neutral is, of course, a big range, as creeping freeway traffic means none, while some of the traffic lights around here can be as long as 1:20 to 2:30.

I suppose could pull an average speed number of your gps. The Subaru’s log average speed per trip in gps but not trip computer.