Gas Mileage Decrease

[Neutron]

I have a 2007 Silverado Ext Cab with the 5.3L AFM engine. I consistantly until about a month ago was able to easily average 18 MPG City/Highway mix. Now I'm lucky if I can average 16.5 MPG.

 

I have 38,500 miles on the clock. I am still on the original tires though that's going to change soon.

 

Could it be the stock spark plugs?

[Jubei69]

Thats a good question, i know when i have to change my sparks for the 1st time, i'm going with Boshe Platinums. Were in DFW are you? I live in Carrollton, but work in Dallas.

[nootron69]

I have a 2007 Silverado Ext Cab with the 5.3L AFM engine. I consistantly until about a month ago was able to easily average 18 MPG City/Highway mix. Now I'm lucky if I can average 16.5 MPG.

 

I have 38,500 miles on the clock. I am still on the original tires though that's going to change soon.

 

Could it be the stock spark plugs?

 

More than likely, it is a direct result of the crappy winter-blend gas they force down our throats...assuming you are not overdue for normal maintenance. It happens every year, and I only noticed it last year prior to going to Iraq. A co-worker told me winter blends change, but I didn't give him the credit cuz I thought he was a little slow. Turns out I am the fool, a lot of peeps make mention of this here on this forum and I have learned it is true since then. BTW, nice name...mine is due to my last name...LOL

[pwall]

Would they use 'winter blend' gas down in Texas though ?

[Neutron]

An overdue oil change was my first thought too, but I got the oil changed 2 weeks ago and got full synthetic done this time which doesn't seem to make a change.

 

The air filter is a drop in K&N and I am using an Airaid air intake, but I installed those over the summer and had seen a slight increase in mileage from that.

 

I thought about putting E3s in once I get to the point of needing to install new plugs.

[Bowtie2Sierra]

It has been colder than usual in the Dallas area lately. It takes longer for the engine to warm up which will hurt your MPG a bit. That could be some of it.

[nootron69]

Would they use 'winter blend' gas down in Texas though ?

 

I live in PA, but if I know big business, my guess would be yes, they wouldnt discriminate petrol shipments between north and south! Any input from the south side of the house?

[dlstewart01]

An overdue oil change was my first thought too, but I got the oil changed 2 weeks ago and got full synthetic done this time which doesn't seem to make a change.

 

The air filter is a drop in K&N and I am using an Airaid air intake, but I installed those over the summer and had seen a slight increase in mileage from that.

 

I thought about putting E3s in once I get to the point of needing to install new plugs.

 

http://www.performancetrucks.net/forums/sh...hlight=E3+plugs

[nootron69]

An overdue oil change was my first thought too, but I got the oil changed 2 weeks ago and got full synthetic done this time which doesn't seem to make a change.

 

The air filter is a drop in K&N and I am using an Airaid air intake, but I installed those over the summer and had seen a slight increase in mileage from that.

 

I thought about putting E3s in once I get to the point of needing to install new plugs.

 

http://www.performancetrucks.net/forums/sh...hlight=E3+plugs

 

 

Welcome home, Don (not a thread hi-jack, just sincerity from another vet)

[dlstewart01]

An overdue oil change was my first thought too, but I got the oil changed 2 weeks ago and got full synthetic done this time which doesn't seem to make a change.

 

The air filter is a drop in K&N and I am using an Airaid air intake, but I installed those over the summer and had seen a slight increase in mileage from that.

 

I thought about putting E3s in once I get to the point of needing to install new plugs.

 

http://www.performancetrucks.net/forums/sh...hlight=E3+plugs

 

 

Welcome home, Don (not a thread hi-jack, just sincerity from another vet)

 

 

Thanks a bunch. see this on winter fuel...

 

THE TRUTH ABOUT WINTER GAS.

 

BY JOHN HUNKINS

 

 

 

As l write this, a suffocating blanket of snow clouds looms on the horizon while thousands of tanker trucks with winter gas roll inexorably toward gas stations in the Northeast and Midwest. In spite of the fact that I'm not a meteorologist, I know exactly what the clouds and cold weather will bring. Yet though I am an automotive journalist, I don't have the foggiest idea of what chemical grog fills those shiny stainless-steel tanks. It's surely got to be bad, no?

 

And as winter's pall approaches New Jersey once again, the CSK office grumblings about winter gas resurface. While joining the ritual chorus of nay-sayers, I found myself thinking, What the hell do I really know about winter gas? Or for that matter, what do I know about fuel? Nothing.

 

Funny how we're all experts on making horsepower, but nobody knows anything about fuel other than pour magic juice in, engine go boom-boom. Considering that horsepower comes from the fuel and not the high-dollar parts, wouldn't you say there's a pretty big gap in the information super highway? The realisation made me feel awkward, like a heart surgeon who doesn't know basic first aid.

 

To satisfy my curiosity about fuel in general and winter gas in particular, I put in a call to Thomas Hart, a fuel chemist with a master's degree from Georgia State University. He's designed many spec fuels for racing, including Formula One, NASCAR, NHRA Pro Stock and motorcycles, and has previously owned his own race fuel company, Turbo Racing Gasoline.

 

Thomas explained that gasoline is made up of many different chemicals, or components, not just one uniform molecule. Smaller, lighter components have a high volatility (they evaporate easily) and boil at a lower temperature, whereas heavier, more complex components don't evaporate as easily and boil at a higher temperature.

 

Each fuel has its own unique signature, called a distillation curve; think of it as a recipe. The distillation curve tells the chemist which components are in the fuel and what their weights (e.g., their boiling points) and quantities are in relation to each other. A simplistic way of looking at the distillation curve would be to list all the fuel's components on a sheet of paper with the heaviest ones at the bottom and the lightest ones on the top.

 

The trick is to have the right fuel for the right time of year. In the summer, when the temperature is high, the presence of too many light components will cause the fuel to evaporate too readily. This can result in vapour lock, an over-rich mixture and excessive evaporative emissions. In the winter, too many heavy components keep the fuel from evaporating, causing hard starting, a lean mixture, heavy hydrocarbon emissions and poor converter light-off.

 

Obviously, since we can't change the weather, we have to use a fuel that will optimize performance and emissions for a particular climate. To do this, fuel manufacturers use heavier components in the summer and lighter components in the winter. This is a simplification of things, but it's close enough for government work.

 

For reformulated winter gas, lighter, low-boiling-point components are added to the gasoline to increase volatility. This makes your car easier to start and accelerates converter light-off, thus lowering emissions. That's the official line on reformulated gas.

 

And now for the teaser. According to Thomas, one of the most popular compounds gasoline refiners used to pump up the brew is called methyl tertiary butyl ether (MTBE).

 

"'MTBE has several good things about it" says Thomas. "One, it boils in a range where the components have a fairly poor octane value. MTBE enhances the octane in the distillation curve. It fills in a good hole there around normal hexane and normal heptane. MTBE has an extremely high octane number, over 108. You've normally got some real junk [in the distillation curve]. [MTBE also] helps on acceleration and cold starting. On a carbureted car, it helps on fuel distribution." Gearhead translation: MTBE is a big check in the horsepower column.

 

With a little fuel chemistry under my belt, I called Mitch Markusich, the proprietor and head brewmaster of PRO Racing Fuels in Mississauga, Ont., Canada.

 

"The essential difference between summer fuels and winter fuels is the vapor pressure," says Mitch. "Manufacturers do this by pumping up the mixture with light-end components like butane, propane and isobutane." The caveat, according to Mark is that these components all have high octane values as well.

 

Shoring up the positive aspects of additives like MTBE, which Thomas earlier asserted, Mark said, "Another major property in [reformulated winter gasoline] is the use of oxygen-bearing ether compounds like MTBE, ETBE (ethyl tertiary butyl ether) and ethanol. It's like pouring liquid oxygen into the combustion chamber. The engine doesn't have to draw the oxygen in because it's already available in the fuel."

 

To illustrate his point, Mark pointed out that in Canada, where his racing fuels are made and used, the government doesn't allow the use of lead in racing fuels. Instead, PRO uses (among other components) MTBE to increase the oxygen content and octane of its fuels. Mark also pointed out that oxygen-bearing compounds like propylene oxide (a fuel additive outlawed in many racing organizations) and nitromethane have a considerable amount of oxygen in their makeup, over 5O percent in the case of nitromethane (By comparison, a 14-15 percent constitution of MTBE would give pump gas around a 2 8 percent oxygen content.)

 

So what does all this mean? Obviously winter gas can't be compared to race fuel; the recipes are too dissimilar. Pump gas must adhere to ASTM specification D4814, which puts specific limits on the composition of highway fuel. But within these limits, there is some blending flexibility. And in many Northern states, there is also the requirement for reformulated fuels.

 

Here's the poop: As specified by state law, reformulated winter gas contains any number of lighter, lower-boiling-point hydrocarbons (butane, propane, etc.) that just so happen to have an excellent octane value. Added to this may be any number of oxygen-bearing ether compounds (MTBE, ETBE, ethanol) that improve emissions and also have a relatively high octane blending value.

 

So what's all the bad hype for? Price, for one thing "It's actually more expensive to make reformulated winter gas than normal, summer fuel, ' says Thomas Hart. Lower fuel economy is another concern.

 

"The oxygen-bearing compounds displace fuel components, so it takes more fuel to get the job done. Normal gasoline has a stoichiometric ratio of 14.7:1, reformulated winter fuel runs between 14.3 and 14.4:1," says Mitch Markusich.

 

And the complaints about poor performance? Mitch says, "When people bitch about the fuel, it's not really the fuel's fault. The weather is largely responsible; after all, it is winter. Low cranking voltage in the battery, increased oil viscosity, atmospheric condensation in underground fuel tanks and so forth."

 

The bottom line is that when it's cold, winter gas seems to be the hot ticket for performance enthusiasts. Not only is the dense winter air good for horsepower, but the higher oxygen content and octane value of winter gas make the pot sweeter And as for fuel economy and price? When did that ever get in the way of having a good time behind the wheel? It s just too bad we have to deal with all that snow and ice".

[txab]

Would they use 'winter blend' gas down in Texas though ?

 

Yes, the blend changes here too. Every year I loose about 1.5 mpg through the "winter" months. There are different blends for different parts of TX. It's more uniform in winter months, but in summer months there are regional blends for the state. 50 miles east of me has a different blend from my area.

 

 

 

 

BTW, neutron, it's not your plugs. Plugs are good to go for lots more miles yet.

[Tsmith]

Well I live in South Mississippi and its been rather colder than the norm down here too. Also have noticed an overall average of 1.5 mpg decrease in fuel mileage over this past summer. Never gave the fuel blend a thought as to the culprit.

[Visegrip117]

The fuel blend plays a big factor in the mileage decrease.

 

I don't know about yall but on cold mornings, I walk outside and crank my truck, turn on the heater and then go back inside and wait for my truck to warm up.

 

The whole time I'm waiting for the truck to warm up, it's sitting there getting 0 mpg. Thereby reducing my overall MPG.

 

Just something to keep in mind.

[Neutron]

I live in the Plano area.

 

The only other thing I've noticed is a rattling sound coming from the passenger side of the engine compartment when accelerating in the lower RPMs.

[Stex]

Give BG-44K a try. It will help with injectors and valve deposits. May try running gas with techron (texaco/chevron) as this helps same. As mentioned above, I think the cold keeps the truck in closed loop longer and I think that hurts MPG. I know I took a short trip the other night and the engine never got to 210 degs.

Yes we do have winter/summer blends. Plugs should not be a problem. I would stay with oem as have heard poor reports on other than oem plugs.