Gas Mileage....It's backwards!

flyboyron · September 5, 2019

When I bought my 09 Silverado, the sticker said 16 city and 21 highway.

Well owning it for almost 10 years now, I was only getting maybe 17 driving to work on the freeway and figured even less around town.

I have the 3:73 rear end so the towing package would affect my mileage and I was ok with that.

A few weeks ago one of the two freeways in my area is having lane closures for the next 2 1/2 years to add lanes and they are telling people to take the other freeway, the one I use.

Of course the freeway I use is already crowded and a 25 minute drive takes almost 45 minutes. There are 10 - 20 min delays showing on the GPS everyday.

So I decided to take a 30 mile route which goes around all the freeways and it takes me almost 50 minutes to get to work.

When I ride my bike, it is a nice relaxing ride. I have also noticed it is not a bad drive in the truck also.

Today, I decided to check my mileage and driving at speeds between 40 and 60 mph I am getting 19.9 mpg.

I think GM should have reversed the numbers on the sticker.

I am all excited now.

riverbanks · September 5, 2019

You probably coast some on the back road?

aseibel · September 5, 2019

45-55 mpg is the best for mpg. Basically the slowest the engine can still drive in top gear.

Anything faster than that and you increase air resistance dramatically. What speed do you drive on the freeway if traffic isn't in your way?

MaverickZ71 · September 5, 2019

You're doing better than my '09 5.3L 6 spd 4x4 3.42 gear. My sticker said 14 city and 19 hwy. I usually get 10 town (remote starting) and 16-17 hwy (65-70mph) [hand calculated] in 2WD, using premium fuel and now with highway tires instead of the factory All Terrains. And I drive easy. Speedometer and odometer have been found to be correct when compared to GPS. It pings if I use regular. And it still eats some oil, despite having the AFM TSB for oil usage done. The average fuel economy and the gallons used shown in the DIC display have averaged being 7+% overoptimistic since new (I have seen them be 12-14% off once in a while).

Mikebtte · September 6, 2019

If I slow down and drive slow in my truck I get better fuel mileage than if I am running 75 in the fast lane. I have figured this to be in relation to drivers in front of me causing me to slow down and than have to speed back up. Maintaining a consistent slower speed will give you better fuel mileage. Stop and go or even slow and go kills fuel mileage. You driving 40-60 is possibly more maintained than on the interstate. Due to people driving in wrong lanes and being distracted, Hwy driving is no longer efficient.

aseibel · September 9, 2019

On 9/6/2019 at 9:41 AM, Mikebtte said:

I have figured this to be in relation to drivers in front of me causing me to slow down and than have to speed back up.

Maintaining a consistent slower speed will give you better fuel mileage. Stop and go or even slow and go kills fuel mileage. You driving 40-60 is possibly more maintained than on the interstate. Due to people driving in wrong lanes and being distracted, Hwy driving is no longer efficient.

To elaborate on your point: If you drive for an hour at exactly 80 and I drive for an hour at exactly 60, I will destroy your fuel mileage. (But they also say time is money, haha. So you will be 20 miles farther down the road than me too.) My truck can run around 25 mpg at 60 mph (as long as no headwind) but increase my speed to 70 mph and now it takes favorable wind conditions to break 20 mpg. The speed makes a huge difference because of your increased air resistance and drag.

If you are constantly hitting brakes and then accelerating on the highway, no matter what the speed or vehicle, you are also wasting fuel. Drive with the flow of traffic and life is a lot less stressful.

bg1988 · September 10, 2019

On 9/5/2019 at 12:09 PM, flyboyron said:

When I bought my 09 Silverado, the sticker said 16 city and 21 highway.

Well owning it for almost 10 years now, I was only getting maybe 17 driving to work on the freeway and figured even less around town.

I have the 3:73 rear end so the towing package would affect my mileage and I was ok with that.

A few weeks ago one of the two freeways in my area is having lane closures for the next 2 1/2 years to add lanes and they are telling people to take the other freeway, the one I use.

Of course the freeway I use is already crowded and a 25 minute drive takes almost 45 minutes. There are 10 - 20 min delays showing on the GPS everyday.

So I decided to take a 30 mile route which goes around all the freeways and it takes me almost 50 minutes to get to work.

When I ride my bike, it is a nice relaxing ride. I have also noticed it is not a bad drive in the truck also.

Today, I decided to check my mileage and driving at speeds between 40 and 60 mph I am getting 19.9 mpg.

I think GM should have reversed the numbers on the sticker.

I am all excited now.

12 hours ago, aseibel said:

To elaborate on your point: If you drive for an hour at exactly 80 and I drive for an hour at exactly 60, I will destroy your fuel mileage. (But they also say time is money, haha. So you will be 20 miles farther down the road than me too.) My truck can run around 25 mpg at 60 mph (as long as no headwind) but increase my speed to 70 mph and now it takes favorable wind conditions to break 20 mpg. The speed makes a huge difference because of your increased air resistance and drag.

If you are constantly hitting brakes and then accelerating on the highway, no matter what the speed or vehicle, you are also wasting fuel. Drive with the flow of traffic and life is a lot less stressful.

so at 70MPH whats the instant mpg reading? mine is between 35MPG and 45MPG at 70MPH in v4 mode in v8 mode it's 27MPG instant mpg..??

v8 6.0L with VVT

Active fuel management will stay on tell 80-82MPH. it might be HIGHER but I have not tried..

it has a 3.08 rear end (Highway Gearing )

flyboyron · September 10, 2019

I will have to check my mpg at speed.

I do not use the V4 option right now, I got one of those "Range" device to stop the engine from going into V4 mode.

I read according to the TSB that I should remove the oil pan and put a cover on the oil pressure relief valve to prevent oil from caking up on the bottoms of the pistons and rings, causing it to burn oil.

I just figured it was easier to put the Range on and my mileage has not suffered.

bg1988 · September 10, 2019

9 minutes ago, flyboyron said:

I will have to check my mpg at speed.

I do not use the V4 option right now, I got one of those "Range" device to stop the engine from going into V4 mode.

I read according to the TSB that I should remove the oil pan and put a cover on the oil pressure relief valve to prevent oil from caking up on the bottoms of the pistons and rings, causing it to burn oil.

well that happens when the oil is not changed enough 4k oil changes does the job i only use it for highway no towing( )

aseibel · September 10, 2019

12 hours ago, bg1988 said:

so at 70MPH whats the instant mpg reading? mine is between 35MPG and 45MPG at 70MPH in v4 mode in v8 mode it's 27MPG instant mpg..??

Is this question a joke? The instant MPG depends on 100 variables and could be anything from 10 - 99.

It doesn't mean anything to anyone who isn't in your truck at the instant you read it.

Yeah, if your're in V4 mode, it will read higher because you are either on flat or downhill grade. If you are on uphill grade the engine switches to V8. Mine switches back and forth more than once per minute, since we have a lot of gentle rolling terrain here. Instant MPG is totally situation dependent.

To get any meaningful data you need to track whole trips/ whole tanks of gas/ multiple trips/tanks, or many years of driving.

bg1988 · September 10, 2019

avg 23mpg on the highway I have a few 26MPG and 25MPG 24MPG fill ups on the same route..

I have a fulley log going with 7k miles it did slump a bit when i had some issues but i fixed it. so it's in good shape now..(electrical issues)

I just need to fix my rear pad as it's dragging

Grumpy Bear · September 10, 2019

13 hours ago, flyboyron said:

I will have to check my mpg at speed.

I do not use the V4 option right now, I got one of those "Range" device to stop the engine from going into V4 mode.

I read according to the TSB that I should remove the oil pan and put a cover on the oil pressure relief valve to prevent oil from caking up on the bottoms of the pistons and rings, causing it to burn oil.

I just figured it was easier to put the Range on and my mileage has not suffered.

In addition to your previous post in this thread.....

If you see no 'statistical' difference between AFM and non-AFM then your AFM wasn't active much to begin with and that sounds about right given you road speeds. AFM is a load based system.

Rings don't "cake up" because of too much oil. They cake up because the oil turns solid given enough heat and time and they stick. Oil rings control the application of oil. If they stick they can't do their job and ring #2 becomes flooded. Control oil temperature and change the oil often enough to prevent lacquer and sludging.

Grumpy Bear · September 10, 2019

On 9/5/2019 at 3:03 PM, aseibel said:

45-55 mpg is the best for mpg. Basically the slowest the engine can still drive in top gear.

Anything faster than that and you increase air resistance dramatically. What speed do you drive on the freeway if traffic isn't in your way?

43 to 55 is where my truck lives and thrives. This summers hand calculated average is over 30 mpg. (June-July-August) Her lifetime average is 27.5 mpg. That includes all seasonal variations and Northern Illinois conditions over a 3 year 100,000 mile span. V6 - 6 speed. It also includes individual tanks at all sorts of speeds. (35 to 75 mph)

aseibel is on the money. Even 60 mph takes a large hit. Part of that is frontal area and drag but that compounds the loss as the AFM isn't active much then either. Below 55 it will stay on even on mild inclines and with any tailwind the only two things that will shut it off are a grade over 3% that is over 1,500 fleet long and...timing out. (Once up to heat of course)

On 9/5/2019 at 2:09 PM, flyboyron said:

A few weeks ago one of the two freeways in my area is having lane closures for the next 2 1/2 years to add lanes and they are telling people to take the other freeway, the one I use.

Of course the freeway I use is already crowded and a 25 minute drive takes almost 45 minutes. There are 10 - 20 min delays showing on the GPS everyday.

So I decided to take a 30 mile route which goes around all the freeways and it takes me almost 50 minutes to get to work.

When I ride my bike, it is a nice relaxing ride. I have also noticed it is not a bad drive in the truck also.

Today, I decided to check my mileage and driving at speeds between 40 and 60 mph I am getting 19.9 mpg.

I think GM should have reversed the numbers on the sticker.

I am all excited now.

And now you know why.

On 9/6/2019 at 9:41 AM, Mikebtte said:

If I slow down and drive slow in my truck I get better fuel mileage than if I am running 75 in the fast lane. I have figured this to be in relation to drivers in front of me causing me to slow down and than have to speed back up. Maintaining a consistent slower speed will give you better fuel mileage. Stop and go or even slow and go kills fuel mileage. You driving 40-60 is possibly more maintained than on the interstate. Due to people driving in wrong lanes and being distracted, Hwy driving is no longer efficient.

Boy is this on the money. I can drive 55 mph on the Interstate and get better mileage than 55 mph on primary highways through small rural towns. It's about even when rural roads are driven at 50 mph. Just information but it isn't that Hwy isn't more efficient than city, it is. It just isn't as efficient as stead Eddy on the Interstate (outside city and off peak hours).

There is also this. Interstates, by and large, have less undulation than state and federal roads. It's by design. IKE wanted to land B-52's if need be on Interstates.