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Why Am I Getting 13 Mpg!?

crepitus

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crepitus Enthusiast

crepitus

Posted
Posted

My 08 Sierra has 2500 miles on it. I am averaging 13 MPG. With my old 06 Sierra with the same 5.3 motor i was averaging 17 MPG. I do let the truck warm up more now with the remote start. Could that make a difference? And my last truck had 3.42 gears and this one has 3.73. I just got a Black Bear tune and he said the motor is running good. What gives?

DBVille Enthusiast

DBVille

Posted
Posted
My 08 Sierra has 2500 miles on it. I am averaging 13 MPG. With my old 06 Sierra with the same 5.3 motor i was averaging 17 MPG. I do let the truck warm up more now with the remote start. Could that make a difference? And my last truck had 3.42 gears and this one has 3.73. I just got a Black Bear tune and he said the motor is running good. What gives?
Warming up the truck will not help the mileage. 3.73 gears versus 3.42 - uhhhh....given the same tranny, 10% higher engine speed means worse gas mileage. More horsepower as well? More weight?

 

Oh, and the tune won't make it get worse mileage, but using that newfound power sure will!!

urbancowboy Enthusiast

urbancowboy

Posted
Posted

i've noticed a big drop in fuel mileage since the cold weather came... tried diff. gas stations no diff. i'm lucky to get 225 miles for a tank of gas in the city

superjim Senior Enthusiast

superjim

Posted
Posted
Oh, and the tune won't make it get worse mileage, but using that newfound power sure will!!

 

 

Tell me about it.

Just made a round trip from North Texas to Florida.

It was really hard sometimes NOT to use it.

It runs so easy at 90 / 100 but does get a little better mileage if you hold it down to 80 / 85.

The power was always there for the asking... just mash the skinny pedal. :lol::uhoh::D

Z71Adrenaline Enthusiast

Z71Adrenaline

Posted
Posted

That winter blend gas must really suck. Mine's mechanically identical to yours, except that it is 4WD, and the worst I have ever gotten was in the 17s. I average 19-20 mixed. Best tank was around 22.5 mpg. I'm at 26k miles now.. Wonder what the deal is?

Z_71_steve Enthusiast

Z_71_steve

Posted
Posted

could it be because of the different blends of gas in the winter? my truck normally gets around 17-18 in the warm weather and in the winter i average like 60 miles to a 1/4 tank?

 

steve

Ranger Senior Enthusiast

Ranger

Posted
Posted

I have about 20,400 miles on mine and I average about 12.5 to 13...I get 16-17 on highway trips. I do live in a pretty congested city and often carry construction materials...I also have 33" tires with a mild lift so I'm sure none of that helps me much. I haven't done a real highway trip with my bed cover though so it may be up somewhat higher in that respect.

 

Definitely gonna be doing a tune soon, getting tired of the throttle lag...Was in a little drag race with my boss' F-150 earlier and all my truck wanted to do was rev but not pull.

superjim Senior Enthusiast

superjim

Posted
Posted

Until your engine reaches normal operating temperature, it runs in open loop mode. After reaching normal temp, it goes into CLOSED LOOP mode.

 

In cold weather it naturally takes longer for the engine to warm up, so it stays in OPEN LOOP mode a lot longer.

 

When it is running in open loop, it runs RICHER than when it is in closed loop mode. Kinda like the old days when the choke was on a little bit.

 

Never mind... the young guys have never driven a truck with a choke :lol::uhoh: so they probably don't know what I am talking about.

 

About the Ethanol.... in my car or my truck ... I can see a DISTINCT difference in mileage when I am and am NOT in an area that uses Ethanol.

 

Another thing to take into consideration.... if you let it warm up for a while before driving... remember, that when it is idling it is burning fuel, but getting ZERO mpg. That will also pull your average mileage down. Sometimes quite a bit, because it is sitting there running in OPEN LOOP till it warms completely up.

DBVille Enthusiast

DBVille

Posted
Posted
Until your engine reaches normal operating temperature, it runs in open loop mode. After reaching normal temp, it goes into CLOSED LOOP mode.

In cold weather it naturally takes longer for the engine to warm up, so it stays in OPEN LOOP mode a lot longer.

 

When it is running in open loop, it runs RICHER than when it is in closed loop mode. Kinda like the old days when the choke was on a little bit.

 

Never mind... the young guys have never driven a truck with a choke :D:D so they probably don't know what I am talking about.

 

About the Ethanol.... in my car or my truck ... I can see a DISTINCT difference in mileage when I am and am NOT in an area that uses Ethanol.

 

Another thing to take into consideration.... if you let it warm up for a while before driving... remember, that when it is idling it is burning fuel, but getting ZERO mpg. That will also pull your average mileage down. Sometimes quite a bit, because it is sitting there running in OPEN LOOP till it warms completely up.

Not quite correct. Open loop means it is running without feedback from the O2 sensor. Yes, it will run richer, but it typically takes minutes, or less. At 60F mine goes Closed Loop in 20 seconds. I believe the big reason for the need of a richer mixture before warming up with a carb is related to the lack of fuel atomization (evaporation) when cold. Gas will condense against the cold intake manifold. Not nearly as much of a problem with fuel injection than a carb (with a choke - manual or electric).

 

It is correct that in cold weather it will take longer, but with heated O2 sensors, not very long. Mileage will be worse when cold - while in closed loop, but before warming up- but I have no idea how much worse.

pennzoil29 Senior Enthusiast

pennzoil29

Posted
Posted

This has been discussed a 100 time's. The winter air is densor, you have winter blend gasolines, etc. I will get 14/15 mpg in the summer, and 10/11/ in the winter. Damn, I just smelled a cigarette. :D

craig melanson Enthusiast

craig melanson

Posted
Posted
My 08 Sierra has 2500 miles on it. I am averaging 13 MPG. With my old 06 Sierra with the same 5.3 motor i was averaging 17 MPG. I do let the truck warm up more now with the remote start. Could that make a difference? And my last truck had 3.42 gears and this one has 3.73. I just got a Black Bear tune and he said the motor is running good. What gives?

 

i use 4lts per 100k more in winter warm it up alot with remote start

66nova Senior Enthusiast

66nova

Posted
Posted
I do let the truck warm up more now with the remote start

 

 

Go one tank without using it. It makes a huge difference.

 

And winter blend...yes

colder air...yes

not many miles...yes

 

All effect it, but I bet you will notice a huge difference not letting it sit and idle as much. But you are in NJ so I'm thinking the loss is probably worth it right now.

crepitus Enthusiast

crepitus

Posted
  • Author
Posted
That winter blend gas must really suck. Mine's mechanically identical to yours, except that it is 4WD, and the worst I have ever gotten was in the 17s. I average 19-20 mixed. Best tank was around 22.5 mpg. I'm at 26k miles now.. Wonder what the deal is?

mine is 4WD as well.

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